Question

explain meiosis .....and its steps with a neat and labelled diagram.....​

Answer 1

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$\huge\mathfark\blue{Meiosis}$

Meiosis is a special type of cell division that reduces the chromosome number by half, creating four haploid cells, each genetically distinct from the parent cell that gave rise to them. This process occurs in all sexually reproducing single-celled and multicellular eukaryotes, including animals, plants, and fungi.

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$\huge\mathfrak\orange{Steps}$

Meiosis I

The first meiotic division is a reduction division (diploid → haploid) in which homologous chromosomes are separated 

P-I: Chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

M-I: Spindle fibres from opposing centrosomes connect to bivalents (at centromeres) and align them along the middle of the cell

A-I: Spindle fibres contract and split the bivalent, homologous chromosomes move to opposite poles of the cell

T-I: Chromosomes decondense, nuclear membrane may reform, cell divides (cytokinesis) to form two haploid daughter cells

Meiosis II

The second division separates sister chromatids (these chromatids may not be identical due to crossing over in prophase I) 

P-II: Chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)

M-II: Spindle fibres from opposing centrosomes attach to chromosomes (at centromere) and align them along the cell equator

A-II: Spindle fibres contract and separate the sister chromatids, chromatids (now called chromosomes) move to opposite poles

T-II: Chromosomes decondense, nuclear membrane reforms, cells divide (cytokinesis) to form four haploid daughter cells 

The final outcome of meiosis is the production of four haploid daughter cells

These cells may all be genetically distinct if crossing over occurs in prophase I (causes recombination of sister chromatids)

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$\huge\mathbb\red{Thank\:you}$

Answer 2

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Biology Dictionary

Meiosis

Meiosis Definition

Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of chromosomes in a cell before reproduction. Many organisms package these cells into gametes, such as egg and sperm. The gametes can then meet, during reproduction, and fuse to create a new zygote. Because the number of alleles was reduced during meiosis, the combination of two gametes will yield a zygote with the same number of alleles as the parents. In diploid organisms, this is two copies of each gene.

Function and Purpose of Meiosis

Meiosis is necessary in many sexually-reproducing animals to ensure the same number of chromosomes in the offspring as in the parents. The act of fertilization includes two cells fusing together to become a new zygote. If the number of alleles of each gene is not reduced to 1 in the gametes that produce the zygote, there will be 4 copies of each gene in the offspring. In many animals, this would lead to many developmental defects. In other organisms, polyploidy is common and they can exist with many copies of the same gene. However, if the organism cannot survive if they are polyploidy, meiosis must occur before reproduction. Meiosis occurs in two distinct divisions, with different phases in each.

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