The Consequences of Crossing Over

A chiasma occurs at least once per chromosome pair. Thus, following crossing over, at least two of the four chromatids become unique, unlike those of the parent. (Crossing over can also occur between sister chro-matids; however, such events do not lead to genetic variation because the DNA sequences are identical between the chromatids.) Crossing over helps

During crossing over, homologous chromosomes pair up to form a bivalent. Nonsister chromatids exchange segments.

chromatid a replicated chromosome before separation from its copy polymerase enzyme enzyme complex that synthesizes DNA or RNA from individual nucleotides

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