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 2N 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 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 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 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: