Meiosis Meiosis The process in which the number
Meiosis
Meiosis • The process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell • 2 divisions, Meiosis 1 and Meiosis 2 • Division of the sex cells (haploid cells)
Homologous Chromosomes • Chromosomes in which one set comes from Dad and one set comes from Mom • Similar in size, shape and banding pattern but not genetically identical
Diploid versus haploid cells • Diploid – having 2 sets of inherited chromosomes , 2 sets of genes • Ex. – all body or somatic cells • Represented by 2 N • Haploid – having only 1 set of chromosomes, 1 set of genes • Ex. – sex cells • Represented by N
Meiosis • 1 diploid cell (spermatocyte or oocyte) that contains 46 chromosomes • 2 sets of divisions, 2 PMAT minus the interphase in the middle • Ends with 4 haploid cells
Meiosis I – cell has undergone interphase • Prophase 1 • Homologous chromosomes come together, forms a tetrad (4 chromatids) • Crossing over – process where the chromatids of non-sister chromatids cross, break off, and exchange genetic material • Produces chromatids with new combination of alleles – GENETIC VARIATION – one reason we are not identical to each other.
Metaphase I and Anaphase I • Metaphase I • Paired homologous chromosomes line up across the center of the cell • Anaphase I • Spindle fibers pull each homologous chromosome pair toward opposite ends of the cell
Telophase I and cytokinesis • Telophase I • Nuclear membrane forms around each cluster of chromosomes • Cytokinesis • Forms 2 new cells
Meiosis II – no interphase, no DNA replication • The final four phases of meiosis II are similar to those in mitosis. However, the result is four haploid daughter cells. • Prophase II • Chromosomes, consisting of two chromatids, become visible • NO homologous chromosomes
Metaphase II and Anaphase II • Metaphase II • Chromosomes line up at the middle of the cell • Anaphase II • Paired chromatids separate
Telophase II and Cytokinesis 4 Genetically different haploid cells
Comparing Mitosis and Meiosis • Similarities:
Comparing Mitosis and Meiosis • Differences:
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