Question

When homologous chromosomes crossover what occurs?

Answer 1

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The following things happen when homologous chromosomes cross overs :

1. Two of the chromatids gets tangled which further results in the re sequencing of DNA.

2. Identical pieces of DNA are exchanged by two sister chromatids.

3. The two strands are broken down by protein molecules and then re joined with their homologs.

4. The four DNA strand of the tetrads are broken down and then mixed up.

5. Both the alleles are corrected in order to make them alike.

Answer 2

Crossing-over in homologous chromosomes occurs at the leptotene stage of prophase I in the first meiotic division. It is a physical exchange of chromosomal segments at corresponding positions which give rise to genetic recombination. It may produce new gene combination. Genetic material is neither loss nor gain during crossing-over.