Chapter 3 1 Meiosis Body cells Gametes Sperm

Chapter 3. 1: Meiosis

• Body cells • Gametes • Sperm • Eggs • Meiosis • Haploid • Diploid • Homologous chromosomes

Sexual Reproduction: Multicellular organisms that reproduce sexually have two types of cells: 1) Body cells are cells in your body that reproduce by cell division (mitosis) – Each human body cell has 46 chromosomes 2) Gametes are sex cells – Each human gamete has 23 chromosomes

Sexual Reproduction: Gametes have half the chromosomes of the parent cell • Male gametes are called sperm • Female gametes are called eggs

Sexual Reproduction: Meiosis is the process that makes gametes, cells with half the number of chromosomes • Cells with half the chromosomes of the parent are called haploid • Symbol for haploid = n

Sexual Reproduction: Meiosis is the process that makes gametes, cells with half the number of chromosomes • Cells with a complete set of chromosomes are called diploid • Symbol for diploid = 2 n

Sexual Reproduction: Homologous chromosomes are chromosome pairs, one from each parent

Stages of Meiosis: Meiosis makes four haploid gametes: It has two phases, meiosis I and meiosis II

Meiosis I: Meiosis I is similar to mitosis during interphase and prophase, but different during metaphase and anaphase

Meiosis I: Interphase • Cell grows, makes another set of centrioles • The cell replicates its DNA (chromosomes double)

Meiosis I: Prophase I • Chromosomes thicken and become visible

Meiosis I: Metaphase I • The homologous chromosomes pair up along the equator (the middle of the cell)

Meiosis I: Anaphase I • The homologous chromosomes separate and move to opposite poles

Meiosis I: • Meiosis I makes 2 daughter cells, but each cell has only one of the homologous chromosomes

Meiosis II: • During meiosis II, 1) the homologous chromosomes line up at the equator of the cell 2) Each homologous chromosome is pulled apart to the opposite pole 3) The nuclear membranes reform, and cytokinesis occurs

Meiosis II: • Meiosis II makes 4 daughter cells called gametes

Meiosis vs Mitosis: Parent Homologous cell chromosomes # of daughter chromosomes cells in daughter cells Mitosis 2 n Separate during anaphase 2 2 n Meiosis 2 n Stay together in meiosis I, Separate in meiosis II 4 n