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6.2 Process of Meiosis KEY CONCEPT Gametes have half the number of chromosomes that body cells have. 6.2 Process of Meiosis You have body cells and gametes. • Body cells are also called somatic cells. • Gametes are sex cells: egg and sperm. – Gametes have DNA that can be passed to offspring. body cells sex cells (sperm) sex cells (egg) 6.2 Process of Meiosis Your cells have autosomes and sex chromosomes. • Your body cells have 23 pairs of chromosomes. • Chromosome pairs #1-22 are homologous chromosomes autosomes. • Sex chromosomes, X and Y, determine gender in mammals. – Homologous pairs of chromosomes have the same structure. sister sister – Homologous chromosomes are chromatids chromatids similar but not identical. – For each homologous pair, one chromosome comes from each parent. 6.2 Process of Meiosis • Haploid (n) cells have one copy of every chromosome. – Gametes are haploid – The production of gametes is called gametogenesis Genesis = formation 6.2 Process of Meiosis Body cells are diploid; gametes are haploid. • Fertilization occurs when gametes fuse during sexual reproduction • Diploid (2n) cells have two copies of every chromosome. – Somatic cells are diploid. – Half the chromosomes come from each parent. 6.2 Process of Meiosis Check for understanding • Which type of cell is haploid? a. Skin cell b. Sperm cell c. Somatic cell d. Liver cell 6.2 Process of Meiosis Check for understanding The fusion of gametes is called A. Fertilization. B. Reassortment. C. Meiosis. D. Gametogenesis. 6.2 Process of Meiosis • Meiosis makes haploid cells from diploid cells. – Meiosis occurs in reproductive germ cells (testes & ovaries) – Meiosis produces gametes with half the # of chromosomes as the parent cell. – Unlike the daughter cells of Mitosis, the daughter cells and parent cells are NOT IDENTICAL 6.2 Process of Meiosis Cells go through two rounds (Meiosis I & Meiosis II) of division in meiosis. • Meiosis I and meiosis II each have 4 phases, similar to those in mitosis Meiosis I – Meiosis I occurs after DNA has been replicated. – Pairs of homologous chromosomes separate in four phases (just like in Mitosis-same names of stages) 6.2 Process of Meiosis Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I 6.2 Process of Meiosis • Meiosis II divides sister chromatids* in four phases. • DNA is not replicated between meiosis I and meiosis II. • *remember a sister chromatid = copy of same DNA 6.2 Process of Meiosis • Meiosis differs from mitosis in significant ways. – Meiosis has two cell divisions while mitosis has one. – In mitosis, homologous chromosomes never pair up. – Meiosis results in haploid cells; mitosis results in diploid cells.