E

FIGURE 7-16 Meiosis in detail.

Like mitosis, meiosts can be divided into discrete stages. After DMA replication, homologous sister chromatids pair with one srother lo form structures with font related chromosomes, tor simplicity, only a single chromosome is shown segregating with the blue copy being from one parent and the yellow copy from the oilier. During pairing, chromatids from the different sister chromatids recombine to form a link between the homologous chromosomes called a chiasms. During meUptiase I, the two kmeto-diores of each sistet-chromalid pair attach to one poie of the meiolic spindle. Homologous sister-chrornatid kinetocfiores attach to opposite pofes creating tension that is resisted by the connection between the homology Cntry into anaphase I is correlated with two events whidi together result in the separation of the homologous chromosomes from ore another. The sister-chrornatid cohesion is lost along the arms of the chromosomes and the chiasms between the homologs are resolved. Together, ihese everts result in the separation of the homologs from one another, the sister chromatids remain attached through cohesion at the centromere. Merosis II is very similar to mitosis. During mei-otic metaphase II ¡wo meiotic spindles are formed. As in mitotic metaphase, ihe kineto-chores associated with each sisler-chramatid pair attach to opposite poies of tl;e meiotic spindles. Dunng anaphase II, the remaining cohesion between the sisters is lost and the sister chromatids separate from one another. The four separate sets of chromosomes aie then packaged into nude» and separated into four cells to create four spores of gametes. All DMA molecules are double stranded. (Source: Adapted from Murray A and HuntT 1993. The cell eyefc: The introduction, fig 10 2. Copyright © 1993 by Oxford University Press, tnc Used by permission of Oxford University Press, Inc)

anaphase It

homolog pairing and recombination

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