11 4 Meiosis Chromosome Number Diploid Cells Two

11. 4: Meiosis

Chromosome Number Diploid Cells �“Two sets” �Of chromosomes �Of genes �Body Cells �Represented as 2 N �N = # chromosomes in gamete Haploid Cells �“One set” �Of chromosomes �Of genes �Gametes, Reproductive cells, Sex cells, Sperm/Egg �Represented as N

Homologous Chromosomes �Found in diploid cells �Chromosomes from male parent have corresponding chromosomes from female parent �Carry the same genes

Meiosis �A process in which the # of chromosomes per cell is cut in half �Creates 4 different haploid cells �Involves two divisions

Division I �Chromosomes replicate �Interphase I �Meiosis I �Prophase I �Chromatin condenses to form chromosomes �Homologous chromosomes pair up (Synapsis) � Forms a tetrad (contains four chromatids) �Crossing-over occurs � Sections of chromatids are exchanged, contributing to genetic diversity of species �Metaphase I �Homologous chromosomes line up in pairs across middle of cell �Anaphase I �Spindle fibers pull chromosomes apart to opposite ends of cell

Division II �NO DNA replication �Prophase II �Chromosomes are visible �Metaphase II �Chromosomes line up single file across middle of cell �Anaphase II �Spindle fibers pull chromatids apart to opposite ends of cell �Telophase II �New nuclear membranes form �Cytokinesis splits cells creating four different

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