Introduction to Meiosis - Practice Questions & MCQ

Introduction to Meiosis

• The term ‘meiosis’ was given by Farmer and Moore.
• It can be defined as the types of cell division in which the DNA of the chromosomes replicates only once but the cell divides twice. 
• Hence, it is a type of cell division in which a diploid cell is reduced to a haploid cell. Therefore, it is also called reductional division.
• A diploid cell is the one which has two sets of chromosomes. For example, in humans the diploid number of chromosomes in 46. There are two sets of chromosomes with 23 chromosomes each. These two sets have come from ovum (mother’s) and sperm (father’s).
• Meiosis produces haploid cells from diploid parent cells.
• Haploid cells in humans are called gametes. These have 23 chromosomes, that is, only a single set of chromosome present. The haploid gametes unite to form a diploid zygote.
• Meiosis occurs in the reproductive or germ line cells in the reproductive organs of the organisms.
• In lower plants like algae, it occurs in the zygote because in these plants the main plant body is haploid.

Homologous pair of chromosomes:

• Before proceeding with the concept of meiosis, it is important to know the concept of a homologous pair of chromosomes.
• During mitosis, the chromosomes behave as an individual unit and do not show any attraction of any kind.
• However, during meiosis, chromosomes are seen to present in a paired manner.
• The chromosomes in a pair are called homologous chromosomes or homologues.
• The homologous chromosomes show the same banding pattern when stained because of the presence of the same type of gene loci.
• However, they can differ in the allelic makeup.
• In the diploid cells of humans, there are 23 pairs of homologous chromosomes.

A micrograph showing homologous chromosomes in human cells. Note the pattern of banding in each pair. 

                                Diagrammatic representation of the homologous chromosomes