Question

A dog (Canis familiaris) has 78 diploid numbers of chromosomes. How many chromosomes would be present in its egg cell?

Answer 1

Hint: The dog of species Canis familiaris is a domesticated carnivore of the family Canidae. The dog C. familiaris is the genetic divergence from the wolf. The direct ancestor of the dog no longer exists. It was the first species and the only large carnivore to have been domesticated. The gametes of an organism contain haploid chromosomes in number.

Complete answer: Gametes of an organism are called the reproductive cells. Two types of gametes are formed from the opposite sex organs, i.e. the male gamete and the female gamete. The female gamete is called the egg cells or ova. In gametes, each cell carries only one copy of each parent chromosome. During meiosis I, the 78 chromosomes number in the diploid cell travel to the equator region of the cell, which gets replicated. In the last stage of meiosis I, i.e. Anaphase I, half the 78 chromosomes, i.e. 39 chromosomes will move to each pole of the cell to replicate. During meiosis II, the cells will divide to produce four daughter cells which are all haploid in numbers, which is half of the diploid cell). So, if 2n is the number of diploid cells then the daughter cells will have ‘n’ number of chromosomes from their parent cell. So, all four daughter cells will have 39 numbers of chromosomes each. Therefore, when a dog (Canis familiaris) has 78 diploid numbers of chromosomes, then its egg cells will always carry a haploid number of chromosomes in it. When there is a haploid number of chromosomes, that means only one of the pairs of chromosomes in the body is taking part in the gamete formation. So, if there are a total of 78 chromosomes then half of its number (half of 78) is 39 chromosomes are present in the female gamete or egg cell. So, the egg cell will have 39 numbers of chromosomes. Therefore, the answer is 39 chromosomes would be present in its egg cell.

Note: We should always remember that chromosomes carry the hereditary characters of the cells. The daughter cells have a haploid number of chromosomes that contain hereditary information of both the parents.