2nd October 2019

wikipedia
16

Where does crossing over occur?

Crossing over occurs between prophase 1 and metaphase 1 and is the process where homologous chromosomes pair up with each other and exchange different segments of their genetic material to form recombinant chromosomes. It can also happen during mitotic division, which may result in loss of heterozygosity.

So, what does crossing over do?

crossing over, process in genetics by which the two chromosomes of a homologous pair exchange equal segments with each other. Crossing over occurs in the first division of meiosis. At that stage each chromosome has replicated into two strands called sister chromatids.

How many times does crossing over occur?

It occurs between prophase 1 and metaphase 1 of meiosis. As an exception , it can ALSO OCCUR IN MITOSIS which may result in heterozygosity. But the frequency of crossing over is much higher in meiosis. Cross over events happen approximately 57 times in males and around 75 times in females during meiosis .

Why does crossing over not occur between sister chromatids?

It occurs during meiosis. Crossing over involves the exchange of chromosome segments between non-sister chromatids during the production of gametes. The effect is to assort (shuffle) the alleles on parental chromosomes, so that the gametes carry combinations of genes different from either parent.
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