Question

Why is meiosis essential in sexually reproducing organisms?

Answer 1

An organism produced by the combination of two organism’s genetic material is known as sexual reproduction. These organisms have a mechanism to produce haploid gametes known as meiosis.

Complete answer:
Meiosis is a type of cell division which reduces the number of chromosomes to half. The pairs of chromosomes separate and produce gametes with one chromosome from each pair. Meiosis involves meiosis I and meiosis II, with different stages.
Meiosis I:
Prophase I: Nuclear envelope breaks down, and the chromosomes condense. Centrioles move to opposite poles of the cell, and formation of spindle begins.
Metaphase I: Spindle fibers attach to paired homologous chromosomes that line up along the equator of the cell.
Anaphase I: Spindle fibers shorten, and chromosomes of each homologous pair separate from each other and move toward one pole of the cell, while the other one moves toward the opposite pole.
Telophase I and Cytokinesis: Spindle breaks down, and new nuclear membranes form. Two haploid daughter cells result which go on to meiosis II.

Meiosis II:
Prophase II: Nuclear envelope breaks down and formation of spindle begins in each haploid daughter cell from meiosis I. The centrioles also start to separate.
Metaphase II: Spindle fibers line up the sister chromatids of each chromosome along the equator of the cell.
Anaphase II: Sister chromatids separate and move to opposite poles.
Telophase II and Cytokinesis: Spindle breaks down and new nuclear membranes form. Cytoplasm of each cell divides forming four haploid cells. Each cell has a unique combination of chromosomes.

Note: Meiosis helps in creation of haploid gametes hence creating gametes which have half the number of chromosomes as compared to the organism, thus gametes unite to form an organism which has same number of chromosomes as that of parents. The other significance of meiosis lies in variations. Crossing over in prophase 1 leads to variations which are a cause of the evolution of organisms.