chapter_01
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| chapter_01 [2024/09/01 23:16] – mike | chapter_01 [2026/10/25 00:59] (current) – [Meiosis results in four non-identical daughter cells called gametes] mike | ||
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| Ironically, mitosis and meiosis are also among the topics that biology students are least interested in, and as a result they are also among the topics that students understand the least. These topics are sometimes challenging for students to learn because they are indeed complex; there are a lot of unfamiliar terms used to describe all the different steps of these processes; and students do not always connect the relevance of learning mitosis and meiosis with biology they can directly observe. | Ironically, mitosis and meiosis are also among the topics that biology students are least interested in, and as a result they are also among the topics that students understand the least. These topics are sometimes challenging for students to learn because they are indeed complex; there are a lot of unfamiliar terms used to describe all the different steps of these processes; and students do not always connect the relevance of learning mitosis and meiosis with biology they can directly observe. | ||
| - | Our goal in this chapter is to learn (or review) just enough about mitosis and meiosis to support our learning of genetics, and to minimize jargon where possible. To meet this goal, we will omit many of the important cell biology details. However, students are encouraged to study and review mitosis and meiosis from a cell biology perspective to gain a deeper understanding of cell division. You should also revisit this chapter when you get confused about concepts in later chapters that relate to meiosis. | + | Our goal in this chapter is to learn (or review) just enough about mitosis and meiosis to support our learning of genetics, and to minimize jargon where possible. To meet this goal, we will omit many of the important cell biology details. However, students are encouraged to study and review mitosis and meiosis from a cell biology perspective to gain a deeper understanding of cell division. You should also revisit this chapter when you get confused about concepts in later chapters that relate to meiosis. Finally, you should study [[appendix_a|Appendix A]], which goes into detail on the chromosome mechanics of meiosis using yeast as an example. |
| ===== Understanding chromosomes ===== | ===== Understanding chromosomes ===== | ||
| - | When thinking about mitosis and meiosis from the perspective of genetics, we really only care about how the chromosomes behave. In somatic cells (i.e., any cell that is not a reproductive cell), chromosomes usually exist as pairs. Human cells, for example, contain 23 pairs of chromosomes. Another way to say this is that human cells have 46 total chromosomes. In humans, these chromosome pairs are named by number, from largest to smallest (1 through | + | When thinking about mitosis and meiosis from the perspective of genetics, we really only care about how the chromosomes behave. In somatic cells (i.e., any cell that is not a reproductive cell), chromosomes usually exist as pairs. Human cells, for example, contain 23 pairs of chromosomes. Another way to say this is that human cells have 46 total chromosomes. In humans, these chromosome pairs are named by number, from largest to smallest (1 through |
| - | Without explaining any details about this right now, you probably have at least a vague idea that chromosomes contain genes (an idea we will talk about more in [[chapter_04|Chapter 04]]) and genes control traits (or phenotypes), | + | You probably |
| ===== Mitosis results in two genetically identical daughter cells ===== | ===== Mitosis results in two genetically identical daughter cells ===== | ||
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| - | A conceptual diagram of meiosis of a human cell. Like Fig. 1.1, this diagram only shows 4 chromosomes that comprise two homologous pairs that can be distinguished based on their size. The color coding is a little different to emphasize the maternal and paternal contributions; | + | A conceptual diagram of meiosis of a human cell. Like Fig. 1.1, this diagram only shows 4 chromosomes that comprise two homologous pairs that can be distinguished based on their size. The color coding is a little different to emphasize the maternal and paternal contributions; |
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| - In metaphase I when the tetrads are lined up in the middle of the cell, the orientation of the tetrad is random. Each dyad has an equal chance of facing one side of the spindle as the other. | - In metaphase I when the tetrads are lined up in the middle of the cell, the orientation of the tetrad is random. Each dyad has an equal chance of facing one side of the spindle as the other. | ||
| - | A final word about gametes and somatic cells. The process of sexual reproduction occurs when haploid gametes from opposite sexes fuse. This results in a new somatic cell (called the zygote) that is now diploid. This zygote can undergo mitosis. In some cases such as with yeast, gametes can undergo mitosis to produce additional haploid daughter cells, but in most examples in this book this does not happen - in general, gametes do not further divide. | + | A final word about gametes and somatic cells: The process of sexual reproduction occurs when haploid gametes from opposite sexes fuse. This results in a new somatic cell (called the zygote) that is now diploid. This zygote can undergo mitosis. In some cases such as with yeast, gametes can undergo mitosis to produce additional haploid daughter cells, but in most examples in this book this does not happen - in general, gametes do not further divide. |
| - | Meiosis is worth revisiting often as we explore genetics in subsequent chapters. Also, be careful of confusing prokaryotes (bacteria) with eukaryotes - only eukaryotes go through mitosis and meiosis, whereas bacteria divide by binary fission, which is a different type of cell division. | + | Meiosis is worth revisiting often as we explore genetics in subsequent chapters. Also, be careful of confusing prokaryotes (bacteria) with eukaryotes - only eukaryotes go through mitosis and meiosis, whereas bacteria divide by binary fission, which is a different type of cell division. It is strongly recommended that the serious student at this point study [[appendix_a|Appendix A]], which goes into a deep dive on the details of the chromosome mechanics of meiosis. |
| A final closing note: there is a lot of jargon (specialized vocabulary) associated with mitosis and meiosis. While you can't avoid memorizing and learning these new terms, don't make that your main focus. The most important part of learning about mitosis and meiosis is understanding how the chromosomes move. It's much better to know how chromosomes move and be unsure about the terms, rather than the other way around. | A final closing note: there is a lot of jargon (specialized vocabulary) associated with mitosis and meiosis. While you can't avoid memorizing and learning these new terms, don't make that your main focus. The most important part of learning about mitosis and meiosis is understanding how the chromosomes move. It's much better to know how chromosomes move and be unsure about the terms, rather than the other way around. | ||
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| ===== Questions and exercises ===== | ===== Questions and exercises ===== | ||
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