Question

Which of the following events together restores the normal number of chromosomes in the life cycle?
(a) Mitosis and Meiosis
(b) Meiosis and Fertilization
(c) Fertilization and Mitosis
(d) Only Meiosis

Answer 1

Two types of cell division processes occur in living organisms called equational division and reduction division. Equational division gives the same number of chromosomes while the reductional division leads to a decrease in the number of chromosomes.

Complete solution:
Mitosis is a kind of cell division that helps in the division of the single-cell into two equal parts, thus it is also called the equational division.
Meiosis is also a kind of cell division that results in a reduction of the number of chromosomes for instance primary spermatocytes are diploid (they possess double the chromosome number) but after the meiosis the secondary spermatocytes are haploid (they posses half the chromosome numbers) thus Meiosis reduces the chromosome number into half but Mitosis maintains the equal number of the chromosome.
1. Meiosis leads to the production of germ cells like sperm and egg by reductional division, which leads to a decrease in the number of chromosomes from diploid to a haploid cell and further fusion of the haploid cell give rise to a diploid zygote.
2. It involves two rounds of the division known as meiosis-I and meiosis-II that ultimately result in four cells with only one copy of each paternal and maternal chromosome.
3. Human fertilization is the union of a human germ cell, which usually occurs in the ampulla of the fallopian tube.

So, the correct answer is ‘Mitosis and Meiosis’.

Note:
The chromosome number varies in different organisms, in some organisms mitosis helps in the production of daughter cells from the parent by equational division, which is common in asexual type of reproduction whereas for sexual reproduction meiosis is important.