Genetics Question In crossingover which occurs in Prophase I

Genetics Question:
In crossing-over, which occurs in Prophase I of meiosis, do chromatids participate equally? Do chromatids equally participate in crossing over? Explain. A sample cell shows that recombinant chromosomes did not occur in equal proportions. What are some possible reasons why this occurred?

Solution

Yes, chromatids participate equally in the crossing over process. These form tetrads which are the basis of crossing over. Also, it is important to note that all chromosomes duplicate during S phase of cell cycle.

Let us take the example of chromosome 1. Chromosome 1 will duplicate to form two chromatids. Two copies of chromosome 1 are there. So, two chromatids will be formed by these two chromosomes. In prophase 1 of Meiosis I, these four chromatids will join together to form a tetrad. If heterozygosity is there in alleles, then crossing over will give visible results.

There are many reasons for the fact that recombinant chromosomes do not occur in equal proportions. These can be: