Choose the correct option with respect to the assertion and reason given.
Assertion [A]: During fertilisation, generally one zygote is formed from which the foetus develops.
Reason [R]: The follicles other than graafian follicle degenerate in a process called follicular atresia.
Both [A] and [R] are true and [R] is the correct explanation to [A].
Every month, 6-12 primary follicles undergo various developmental stages to form vesicular follicles. Among these only the largest follicle survives while the others eventually degenerate in a process called follicular atresia. The victorious follicle is called the Graafian follicle and it consists of the secondary oocyte arrested at metaphase II. This oocyte after ovulation can get fertilized. Therefore only one zygote is formed from which a foetus develops. Maturation of more than one follicle leads to multiple pregnancies, twins, triplets, etc. where the foetuses have to struggle in the womb for space and nourishment.