Question

What will be the gametic chromosome number of a cell, if that organism has somatic cells with 40 chromosomes each ?

Answer 1

There will be half the number of chromosomes an organism has in its somatic cells (all other body cells except gametes). For example in humans, the somatic cells contain 46 chromosomes which is the diploid number (2n) and each sperm and egg has 23 chromosomes where one of them is the sex chromosome.

Answer 2

Gametes are haploid, that is they contain half the number of chromosomes of somatic cells of the organism, so as to produce a diploid offspring by the union of two gametes, each with half the required chromosomes. (n+n=2n)

Since, the organism in this case has 20 pairs of chromosomes, a.k.a. 40 in number, one from each pair will separate out (with variations) during the formation of the gamete, so the gametic chromosomes of such species will be 20 in number.