Meiotic Cell Division –Why and How? : A Genetic Perspective

Resonance

article

Rajiva Raman¹ 

[1]Cytogenetics Laboratory Department of Zoology Banaras Hindu Univesity Varanasi 221 005

关键词: Cell division;    mitosis;    yeast;    meiosis;    inducers of meiosis;    haploidy.;   

DOI  :  10.1007/s12045-023-1618-0

学科分类：社会科学、人文和艺术（综合）

来源: Springer

【 摘 要 】

Most somatic cells are diploid with 2 sets of chromosomes.These cells divide at regular intervals. At the time of division,called ‘mitosis’, each chromosome carries two chromatids.As they divide, the daughter cells get one chromatid fromeach chromosome. Thus though the cells retain their chromosomenumber, their DNA content gets half. Prior to thenext division, these cells pass through a phase of DNA synthesisthat recovers the lost DNA and adds a chromatid to eachchromosome. ‘Meiosis’ is a division of cells that leads to thereduction in their chromosome number as well as the amountof DNA to haploidy (1 set of chromosomes and DNA). It isachieved by the cell undergoing two successive divisions withoutthe intervening S phase. These haploid cells differentiateinto gametes which when fused with another gamete make adiploid zygote, the progenitor of an organism. In higher organisms,cells specialised to undergo meiosis are germ cells.In several single-celled organisms too meiosis takes place. Essentiallythe process is conserved throughout the living world.In this article, we try to understand under what conditionsand situations mitotically dividing cells initiate meiosis. Wealso unravel the genetic regulation of its initiation as well asthe process that follows. In the unicellular mould, yeast, underconditions of stress (nutritional, environmental) a set ofIME (inducers of meiosis) genes (IME1, IME2, IME4) get activated.These genes comprise regulators in their promoter regions that inhibit their expression in haploid and unstressed conditions. When activated, IME genes initiate cells into meiosis and induce a cascade of genes that steer the cells towards homologous pairing, recombination, and chromosomal segregationfollowed by another division without the S phase.We will also try to understand the mechanisms of other phenomenaunique to meiosis viz., segregation of chromosomesinstead of chromatid at anaphase I, entry into meiosis II andits execution without passing through the S phase.

【 授权许可】

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