Question

The diagram given below represents a certain phenomenon which occurs during meiosis, Name and explain the phenomenon by using the terms homologous chromosomes, chromatids, crossing over.

Answer 1

Crossing-over is the phenomenon is an exchange of chromatids between homologous chromosomes.

1. Chromosome number is halved in gametes (sex cells) so that on fertilization, the normal number (2n) is restored.

2. It provides for mixing up of genes which occurs in two ways:

(i) The maternal and paternal chromosomes get mixed up during the first (reduction) division as they separate from the homologous pairs.

(ii) While the maternal and paternal chromosomes are separating, the chromatid material very often gets exchanged between the two members of a homologous pair.