TNBGGA: The No Bullshit Guide to Genetic Analysis

One of the goals of genetic analysis is to figure out where genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are physically located on chromosomesplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. relative to one another. This is called mappingplugin-autotooltip__default plugin-autotooltip_bigGenetic mapping: a term describing a variety of different experimental approaches used to determine the physical locations of genes on chromosomes.. In modern times, mappingplugin-autotooltip__default plugin-autotooltip_bigGenetic mapping: a term describing a variety of different experimental approaches used to determine the physical locations of genes on chromosomes. is done by DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. sequencingplugin-autotooltip__default plugin-autotooltip_bigSequencing: the procedure used to determine the sequence of a biological polymer such as DNA, RNA, or protein. Although there are indeed biochemical techniques that can be used to directly sequence RNA or protein, these methods are almost never used in modern molecular genetics research - instead, RNA, but classically it was done through genetic crosses. Even though we rarely use this technique anymore in its original form, it is instructive to learn about it because it illustrates important concepts about recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$, which is still important even in modern mappingplugin-autotooltip__default plugin-autotooltip_bigGenetic mapping: a term describing a variety of different experimental approaches used to determine the physical locations of genes on chromosomes. approaches.

After the discovery of $white$, Morgan's lab found mutantplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. allelesplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence. of many other genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) that are also sex-linkedplugin-autotooltip__default plugin-autotooltip_bigSex linkage: a gene is said to be sex-linked if it maps to a sex chromosome.. Consider another sex-linkedplugin-autotooltip__default plugin-autotooltip_bigSex linkage: a gene is said to be sex-linked if it maps to a sex chromosome. mutationplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. on the $X$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. of Drosophilaplugin-autotooltip__default plugin-autotooltip_bigDrosophila melanogaster: a fruit fly species used in genetics research.: $crossveinless$ ($cv$):

Let's do a cross between a $crossveinless$ male and $white$ female:

All of the F1 daughters from Figure 2 will have two different $X$ chromosomesplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins., which differ at two lociplugin-autotooltip__default plugin-autotooltip_bigLocus (plural form: loci): a physical location of a gene; often used as a synonym for a gene.: $\frac{cv\ \ +}{+\ \ \ w}$. (Note that this genotypeplugin-autotooltip__default plugin-autotooltip_bigGenotype: the combination of alleles within an organism or strain. When used as a verb, it means to determine the genotype experimentally. is not the same thing as $\frac{cv\ \ w}{+\ \ \ +}$!) We want to follow these $X$ chromosomesplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. into the next generation, so we cross these F1 females to wildtypeplugin-autotooltip__default plugin-autotooltip_bigWildtype: a reference strain of an organism that scientists operationally define as “normal” to which mutants are compared. Not to be confused with wild organisms. males, and we look at F2 male flies:

The possible F2 outcomes from this cross are shown in Table 2.

The tiny $Y$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. does not contain either the $cv$ or $w$ genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) (in fact, the $Y$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. barely has any genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-)). Thus, for genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) on the $X$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. such as $cv$ and $w$, examining males only makes it effectively a test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03.. If $cv$ and $w$ segregated independently from each other (i.e., if they followed Mendel's Second Lawplugin-autotooltip__default plugin-autotooltip_bigMendel's Second Law: also called the Law of Independent Assortment. It states that alleles from each genetic loci segregate independently of each other. This “law” actually only applies to unlinked genes.) we would expect that the four combinations of progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. classes ($cv^+ \ \ w^+$, $cv^+ \ \ w^-$, $cv^- \ \ w^+$, $cv^- \ \ w^-$) would appear at the same frequency; that is, the four progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. classes would show 1:1:1:1 ratio. However, we find that there are more males that are parental-like ($cv^+ \ \ w^-$, $cv^- \ \ w^+$) than there are non-parentalplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” (recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.”)-like ($cv^+ \ \ w^+$, $cv^- \ \ w^-$). Specific numbers are given below in Table 3. Genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. such as $cv$ and $w$ do not assort independently if they are located close to each other; they are biased to assort together most but not all of the time. Such behavior is known as linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes..

We already know that $cv$ and $w$ are both sex-linkedplugin-autotooltip__default plugin-autotooltip_bigSex linkage: a gene is said to be sex-linked if it maps to a sex chromosome.; that is, we know they are physically located on the $X$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. But when we perform the cross shown in Figures ref and 3, we observe non-parentalplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” types in the F2 test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03. progenyplugin-autotooltip__defaultProgeny: a synonym for offspring.. Based on the phenotypesplugin-autotooltip__default plugin-autotooltip_bigPhenotype: an observable feature or property of an organism. of the non-parentalplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes, the allelesplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence. appear to have separated and moved from one $X$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. to the other. This implies that there must have been an exchange of chromosomalplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. material (crossing overplugin-autotooltip__default plugin-autotooltip_bigCrossing over: an event where non-sister chromatids exchange material with each other during meiosis I.) in the F1 heterozygousplugin-autotooltip__default plugin-autotooltip_bigHeterozygous: a state for a diploid organism wherein the two alleles for a gene are different from each other. mother when she went through meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs). to form gametesplugin-autotooltip__default plugin-autotooltip_bigGamete: a specialized (usually haploid) cell used for sexual reproduction. Eggs (oocytes) and sperm are gametes..

To see what's really going on we need to look at the chromatidsplugin-autotooltip__default plugin-autotooltip_bigChromatid: a chromosome-like structure, two of which are formed after replication of a chromosome in both mitosis and meiosis. arranged as a tetradplugin-autotooltip__default plugin-autotooltip_bigTetrad: In the context of yeast genetics, a tetrad refers to the four ascospores from a single ascus, which represents the four products of a single meiotic event. In the context of meiosis in general, a tetrad refers to the four chromatids from a set of replicated homologous chromosomes lined up at metaphase I. in prophase I of meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs). in the F1 heterozygousplugin-autotooltip__default plugin-autotooltip_bigHeterozygous: a state for a diploid organism wherein the two alleles for a gene are different from each other. mother.

During prophase I, structures called chiasmataplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. form between non-sister chromatidsplugin-autotooltip__default plugin-autotooltip_bigNon-sister chromatids: Chromatids that are derived from two different chromosomes in a homologous chromosome pair during meiosis I. See also: sister chromatids.. The term chiasmataplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. (kai-as-MAH-tah; singular form is chiasmaplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma.) comes from the Greek letter χ, which is pronounced “kai” and is shaped like the letter X. In Figure 4, a chiasmaplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. forms between chromatidsplugin-autotooltip__default plugin-autotooltip_bigChromatid: a chromosome-like structure, two of which are formed after replication of a chromosome in both mitosis and meiosis. (2) and (3), but chiasmataplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. can form between any two non-sister chromatidsplugin-autotooltip__default plugin-autotooltip_bigNon-sister chromatids: Chromatids that are derived from two different chromosomes in a homologous chromosome pair during meiosis I. See also: sister chromatids. (for instance, you could also form a chiasmataplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. between chromatidsplugin-autotooltip__default plugin-autotooltip_bigChromatid: a chromosome-like structure, two of which are formed after replication of a chromosome in both mitosis and meiosis. (1) and (3)). A chiasmaplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. is simply a structure where physical breaks have occurred on the non-sister chromatidsplugin-autotooltip__default plugin-autotooltip_bigNon-sister chromatids: Chromatids that are derived from two different chromosomes in a homologous chromosome pair during meiosis I. See also: sister chromatids. and they exchange material with each other. More commonly, we use the term “crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma.” both as a noun and a synonym for chiasmataplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma., and as a verb to describe the process.

Crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. between non-sister chromatidsplugin-autotooltip__default plugin-autotooltip_bigNon-sister chromatids: Chromatids that are derived from two different chromosomes in a homologous chromosome pair during meiosis I. See also: sister chromatids. occur at random places during meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs).. In Figure 4, a crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. is shown to occur between $cv$ and $w$, but it can happen anywhere. For instance, it can happen between the centromereplugin-autotooltip__default plugin-autotooltip_bigCentromere: a locus on a chromosome that marks where spindle fibers attach during mitosis and meiosis. and $cv$, or it can happen between $w$ and the end of the chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. The likelihood that a crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. will happen at any specific location on the chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. is roughly the same across the entire chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. In most organisms, there is an average of one crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. per chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. arm per meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs)., although there can be more than one crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. per chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. arm per meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs). (these are called double crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma., triple crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma., etc.).

Because the location of the crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. is random, the frequency of crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. occurring between two points on a chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. depends on the distance between those two points. Crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. between two points that are close together will occur rarely, whereas crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. between points that are far apart will occur more frequently. Geneticists can thus use these random crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. as a tool to measure map distance.

$$\text{map distance} = 100 \times \frac{\text{crossover gametes}}{\text{total gametes}}$$

In essence, map distance between two points is the percent recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ between those two points. We typically use the unit of measures m.u. (which stands for map unitplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM.) or cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. (centiMorganplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM., named in honor of Thomas Morgan) for map distances. We can map the distance between $cv$ and $w$ by doing the cross shown in Figs. 2 and 3 and carefully counting the number of offspring and their different phenotypesplugin-autotooltip__default plugin-autotooltip_bigPhenotype: an observable feature or property of an organism. (Table 3). We look at males only:

In this cross, the recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes are $cv^- \ \ w^-$ and $cv^+ \ \ w^+$. The number of crossoverplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. gametesplugin-autotooltip__default plugin-autotooltip_bigGamete: a specialized (usually haploid) cell used for sexual reproduction. Eggs (oocytes) and sperm are gametes. = $52 + 68 = 120$. Therefore, map distance = $100\times\frac{120}{1000} = 12$ m.u., or 12 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM..

When recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes appear as 50% of the F2 offspring of a test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03., we say the two genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. (this is discussed further below). When recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes appear frequently but are less than 50% (for example, 41%), we say that two genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are weakly linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes.. Conversely, if recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes appear very rarely then we say that two genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are tightly linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. (for example, 5%). It is important to note that once a map distance between two genetic markersplugin-autotooltip__default plugin-autotooltip_bigMarker: an allele of a gene that provides an easily observable phenotype. Markers are usually cloned or least well mapped. They are used as genetic landmarks in various genetic experiments. In some cases, markers do not have easily observable phenotypes and can only be detected using molecular methods (e.g., SNPs or SSRs). has been established, this distance can be used to predict the expected numbers of each type of progenyplugin-autotooltip__defaultProgeny: a synonym for offspring.. For example, if you know that two mutationsplugin-autotooltip__default plugin-autotooltip_bigMutation: a change in the DNA of a gene that results in a change of phenotype compared to a reference wildtype allele. See also: mutant. are 12 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. apart then you should expect that about 6% of the gametesplugin-autotooltip__default plugin-autotooltip_bigGamete: a specialized (usually haploid) cell used for sexual reproduction. Eggs (oocytes) and sperm are gametes. from a cross will be of each of the two recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” classes.

Things get interesting when we make several pairwise crosses between genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. We can use this data to construct a genetic mapplugin-autotooltip__default plugin-autotooltip_bigGenetic map: a map that shows gene positions on chromosomes measured in centiMorgans.. Genetic mapsplugin-autotooltip__default plugin-autotooltip_bigGenetic map: a map that shows gene positions on chromosomes measured in centiMorgans. have the following properties:

1. Physical distance is proportional to frequency of crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. (this approximation actually only holds for short distances of <20 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM.);
2. Distances are approximately additive: mapped points fall on a lineplugin-autotooltip__default plugin-autotooltip_bigStrain or line: refers to a pool or colony of individuals or cultured cells of a desired genotype or phenotype that is mostly homogeneous and can be bred and/or produced in perpetuity for research or commercial purposes. “Strain” tends to be used more for microorganisms and;
3. Maps are internally consistent and concise.

The first genetic mapplugin-autotooltip__default plugin-autotooltip_bigGenetic map: a map that shows gene positions on chromosomes measured in centiMorgans. of any kind was constructed in 1911 by Alfred Sturtevant when he was a sophomore undergraduate student in Thomas Morgan’s lab. It showed the relative positions of several genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) on the Drosophilaplugin-autotooltip__default plugin-autotooltip_bigDrosophila melanogaster: a fruit fly species used in genetics research. $X$ chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins..

It is important to remember that genetic distances are measured using a property of meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs). (genetic recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$) that varies from one organism to another. The relationship between genetic distance and actual physical distance can be summarized in this way:

$$\text{Genetic distance = physical distance } \times \text{recombination rate}$$

The actual relationship between genetic distance in cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. and physical distance in base pairsplugin-autotooltip__default plugin-autotooltip_bigBase pair: a term used to describe how nitrogenous bases (G, A, T/U, and C) in nucleic acids interact with each other via hydrogen bonds to form double-stranded molecules (including dsDNA, dsRNA, and DNA/RNA hybrids). G always pairs with C, and T/U always pairs with A. (bp) of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. depends on the recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ rate, which is different for different organisms. For example, in humans the recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ rate is 1.3 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM./Mbp whereas in yeastplugin-autotooltip__default plugin-autotooltip_bigYeast: in this book, refers to Saccharomyces cerevisiae, a single-celled eukaryotic microbe used as a model genetic organism. See Chapter 02 it is 360 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM./Mbp (1 Mbp = 10⁶ bp). Sometimes recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ rates in the male and female of a species are different. In Drosophilaplugin-autotooltip__default plugin-autotooltip_bigDrosophila melanogaster: a fruit fly species used in genetics research. there is no recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ in males so the genetic distance between markersplugin-autotooltip__default plugin-autotooltip_bigMarker: an allele of a gene that provides an easily observable phenotype. Markers are usually cloned or least well mapped. They are used as genetic landmarks in various genetic experiments. In some cases, markers do not have easily observable phenotypes and can only be detected using molecular methods (e.g., SNPs or SSRs). on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. are always zero when examined by meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs). in the male. In humans the recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ rate (and therefore map distances) in females is twice that of males.

Another issue that often causes confusion concerns the map distances of genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) that are far apart on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. The physical length of a genetic interval is proportional to the frequency of crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. that occur in that interval during meiosisplugin-autotooltip__default plugin-autotooltip_bigMeiosis: a process involving two sequential cell divisions that usually produces four gametes (reproductive cells such as sperm or eggs).. But in a cross, we are not actually counting crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma.; rather, we are counting the number of recombinantplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. that are produced. The frequency of recombinantsplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” provides a good approximation of distance for short intervals but as the interval length increases, double or even triple crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. are possible, making the relation¬ship between frequency of recombinantsplugin-autotooltip__default plugin-autotooltip_bigRecombinant: (adj.) Describing something that has undergone recombination, e.g., recombinant DNA or recombinant offspring. “Non-parental” is a synonym when referring to organisms. (n.) Something that has undergone recombination, e.g., “This fly is a recombinant.” and crossoversplugin-autotooltip__default plugin-autotooltip_bigChiasma (plural: chiasmata): structures shaped like the Greek letter χ (usually Romanized as chi but pronounced “kai”) that form between non-sister chromatids during meiosis I. Chiasmata is the physical manifestation of crossing over. “Crossover” can be used as a synonym for chiasma. not linear. This is discussed further in Appendix A on tetrad analysisplugin-autotooltip__default plugin-autotooltip_bigTetrad analysis: an experimental method to analysis meiosis in yeasts and other fungi. See Appendix A..

If the measured distance in a cross is statistically indistinguishable from 50 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. then we say that the genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes.. In fact, by definition a map distance of 50 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. is the same thing as saying that the two genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) assort independently. But this doesn’t mean that distances greater than 50 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. cannot be obtained. By adding intervals between multiple genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-), longer distances that are meaningful can be obtained. For example, if all the intervals between linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) in the human genomeplugin-autotooltip__default plugin-autotooltip_bigGenome: a dataset that contains all DNA information of an organism. Most of the time, this also includes annotation and curation of that information, e.g., the names, locations, and functions of genes within the genome. As an adjective (“genomic”), this usually is used in the context of are added together the total length of the genomeplugin-autotooltip__default plugin-autotooltip_bigGenome: a dataset that contains all DNA information of an organism. Most of the time, this also includes annotation and curation of that information, e.g., the names, locations, and functions of genes within the genome. As an adjective (“genomic”), this usually is used in the context of (in males) is 2,500 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM.. Genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) that are physically located on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. can be described as being in the same linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. group, even though they might not be linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes.. For example, in Fig. 5.4, we can see that white, which is at map position 1.5 on chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. X, and forked, which is at map position 56.7 also on chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. X, are unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. even though they are on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins.. But we can calculate their map distance by subtracting their map positions (56.7 - 1.5 = 55.2 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. apart).

Exercise 5.3. Design and write out a genetic cross between white and forked to measure their linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes., using information from Fig. 5.4. Draw the tetradplugin-autotooltip__default plugin-autotooltip_bigTetrad: In the context of yeast genetics, a tetrad refers to the four ascospores from a single ascus, which represents the four products of a single meiotic event. In the context of meiosis in general, a tetrad refers to the four chromatids from a set of replicated homologous chromosomes lined up at metaphase I. and the crossing overplugin-autotooltip__default plugin-autotooltip_bigCrossing over: an event where non-sister chromatids exchange material with each other during meiosis I. similar to Fig. 5.2. Calculate the ratios of the test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03. progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. based on the idea that map distance = recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ frequency. It's relatively easy to come up with a number, but it's a little harder to determine if an answer makes sense. Does your answer make sense?

Discussion box: “You can have map distances greater than 50 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM., but you can't have recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ frequencies greater than 50%”. Does this sentence make sense?

Based on the concepts that Morgan's lab developed, we can now define genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) as follows: genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are pieces of hereditary information that have distinct physical locations on chromosomesplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins..

Exercise 5.4. Let's revisit Fig. 2.3 and yeastplugin-autotooltip__default plugin-autotooltip_bigYeast: in this book, refers to Saccharomyces cerevisiae, a single-celled eukaryotic microbe used as a model genetic organism. See Chapter 02. We can imagine that there are four genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) in the yeastplugin-autotooltip__default plugin-autotooltip_bigYeast: in this book, refers to Saccharomyces cerevisiae, a single-celled eukaryotic microbe used as a model genetic organism. See Chapter 02 histidineplugin-autotooltip__default plugin-autotooltip_bigHistidine: Abbreviated as His or H; one of the 20 amino acids that are used to form proteins. biosynthetic pathwayplugin-autotooltip__default plugin-autotooltip_bigPathway: a series of reactions or events that occur in sequence with some common goal or purpose.: his1, his2, his3, and his4. In Chapter 2, we learned that you could determine that these are different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) through complementationplugin-autotooltip__default plugin-autotooltip_bigComplementation: a concept where an additional allele of a gene (usually a wildtype allele) can provide normal function to an organism with a recessive loss of function mutation in that gene. The concept of complementation underlies the complementation test. testing. In a conceptual sense and without worrying about experimental details, what other way can you use to determine if these are different genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-)?

In Chap. 2 we used the symbol “dot” (ꞏ) to separate geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) symbols between which we did not know the linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. status. For instance, writing “shi ꞏ vg” meant that we don't know if shibire and vestigial are linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. or unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes.. In this chapter, we saw that linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) should be written without any separating symbol. For instance, “b vg” indicates that black and vestigial are linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes.. We can write genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) that are on the same chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. this way as well to indicate that they belong to the same linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. group (that is, all the genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) in a linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. group are directly or indirectly linkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. to each other), even if they are over 50 cMplugin-autotooltip__default plugin-autotooltip_bigMap unit (m.u.): a unit of genetic distance defined as 1% recombination. Also called a centiMorgan or cM. apart. For instance, aristaless (al) is at map position 0.0 on chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. II whereas vg is at position 67.0 on chromosomeplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins. II; thus, al and vg are unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. (that is, they are over 50 m.u. apart) but you could write the genotypeplugin-autotooltip__default plugin-autotooltip_bigGenotype: the combination of alleles within an organism or strain. When used as a verb, it means to determine the genotype experimentally. as al vg. Finally, we use a “semicolon” to separate geneplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) symbols to indicate that two genesplugin-autotooltip__default plugin-autotooltip_bigGene: read Chapters 02, 03, 04, 05, and 06 for a definition of gene :-) are not on the same linkageplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. group. For instance, “shi; w” would indicate that shibire and white are unlinkedplugin-autotooltip__default plugin-autotooltip_bigLinkage: two loci are linked to each other if they are less than 50 m.u. apart. Two loci are unlinked if they are either (1) greater than 50 m.u. apart on the same chromosome, or; (2) are on separate chromosomes. and also on different chromosomesplugin-autotooltip__default plugin-autotooltip_bigChromosome: a structure that organizes dsDNA in a cell through interactions with various DNA binding proteins..

Exercise 5.1. Why do we only look at males in the above experiment? What kinds of female F2 progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. would you expect to get? Can you predict their phenotypesplugin-autotooltip__default plugin-autotooltip_bigPhenotype: an observable feature or property of an organism.? Can you predict their genotypesplugin-autotooltip__default plugin-autotooltip_bigGenotype: the combination of alleles within an organism or strain. When used as a verb, it means to determine the genotype experimentally.? Would that information be helpful in measuring recombinationplugin-autotooltip__default plugin-autotooltip_bigRecombination: Recombination can have slightly different meanings depending on context:

* In the context of genetic crosses (usually a dihybrid cross or a test cross), recombination refers to the phenomena where the phenotype of the F2 offspring is different than either parent (P generation). $lox$ frequency between cv and w? Why or why not?

Exercise 5.2: Design and write out a genetic cross between black (b) and vestigial (vg) to map their distance. You will probably want to use a test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03. strategy (you can assume that you have a true breedingplugin-autotooltip__default plugin-autotooltip_bigTrue breeding: a true breeding strain is one that has been inbred for multiple generations. We assume that the vast majority of loci are homozygous in a true breeding strain. b vg double mutantplugin-autotooltip__default plugin-autotooltip_bigMutant: an individual that has a different phenotype than wildtype and likely contains one more mutations that cause this difference. in the lab). Draw the tetradplugin-autotooltip__default plugin-autotooltip_bigTetrad: In the context of yeast genetics, a tetrad refers to the four ascospores from a single ascus, which represents the four products of a single meiotic event. In the context of meiosis in general, a tetrad refers to the four chromatids from a set of replicated homologous chromosomes lined up at metaphase I. and the crossing overplugin-autotooltip__default plugin-autotooltip_bigCrossing over: an event where non-sister chromatids exchange material with each other during meiosis I. similar to Fig. 5.2. Based on the information in Fig. 5.4., what kind of F2 test crossplugin-autotooltip__default plugin-autotooltip_bigTest cross: a genetic cross devised by Gregor Mendel that allows a researcher to easily determine the genotype of an individual that appears wildtype but has an unknown genotype. This assumes you have a tester strain readily available. See Chapter 03. progenyplugin-autotooltip__defaultProgeny: a synonym for offspring. will you get, and what will their frequencies be?