Sexual Reproduction Meiosis

Sexual Reproduction Our body cells all have 46 chromosomes DIPLOID: Two copies of each chromosome - 23 from our mom, 23 from our dad HOMOLOGOUS CHROMOSOME: chromosomes that have the same type of information on them Same length and shape All diploid cells have homologous chromosomes Exception: sex cells (eggs and sperm) have half the number of chromosomes as other body cells HAPLOID: one copy of each chromosome MEIOSIS: type of cell division that halves the chromosome number to make sperm and eggs Cells go from diploid to haploid Make 4 cells from one cell

MEIOSIS Follows the same basic steps as mitosis with one critical difference Steps of both types of cell division: Prophase: nuclear membrane breaking down, centrioles are beginning to form spindle fibers Metaphase: chromosomes line up along equator, spindle fibers attached to chromosomes Anaphase: chromosomes split in half, separate to the poles being pulled by spindle fibers Telophase: chromosomes at poles, nuclear membrane reforms

Meiosis follows the same basic steps of mitosis but begin with tetrads TETRAD: homologous chromosomes come together and move as a unit While homologous chromosomes are side by side, similar pieces of chromosomes can swap, switching genetic material CROSSING OVER Meiosis I: chromosomes form tetrads in prophase Metaphase: Line tetrads up at equator Anaphase: Divide tetrads in half Telophase: first division ends up with two cells that have double stranded chromosomes Meiosis II: divide each cell again to form single stranded chromosomes in each cell - exact same steps as mitosis

COPY DIAGRAM

Crossing Over

DRAW IN NOTES Homologous Not Homologous

 + +  Tetrad COPY INTO NOTES Homologous Chromosome Homologous

Assignment Worksheet: Comparing Meiosis and Mitosis Due next day