Targeting construct: a piece of DNAplugin-autotooltip__default plugin-autotooltip_bigDNA: deoxyribonucleic acid. The genetic material for nearly all life on Earth. engineered in vitroplugin-autotooltip__default plugin-autotooltip_bigIn vitro: taking place outside of a living organism, usually in a test tube or Petri dish. that is used to make a knockoutplugin-autotooltip__default plugin-autotooltip_bigKnockout: a knockout allele is a null allele generated through reverse genetics. alleleplugin-autotooltip__default plugin-autotooltip_bigAllele: a version of a gene. Alleles of a gene are different if they have differences in their DNA sequence..