MCAT Biological and Biochemical Foundations of Living Systems: Passage 17 — Flashcards

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Genes that are located on different chromosomes assort independently. However, genes on the same chromosome can still separate from each other through a process called recombination. During meiosis, when four homologous chromatids form a tetrad, two of the chromatids can cross over, which causes them to break from their chromatid and reattach to the other chromatid. When this crossover event happens between non-sister chromatids that contain different alleles of a gene, recombination takes place and gives rise to genetic diversity. Furthermore, the event can happen at more than one point between chromatids, resulting in multiple crossovers.

Evidence of crossovers can be seen microscopically by the detection of chiasmata. hese structures are thought to remain at the site of crossovers because the chromatids stay tangled together as the cell continues through meiosis. In addition to the detection of chiasmata, geneticists can identify crossover events by tracking the recombination of alleles on either side of the chromatid exchange. This tracking also allows the mapping of distance between genes. There is a direct correlation between the extent of recombination between two linked genes and their distance from each on a chromosome: genes that are far apart recombine frequently. The rates of recombination can also reveal the order of genes on a chromosome because single crossover events are much more likely to occur than multiple crossover events.