Meiosis

Meiosis: creates 4 gametes or haploid cells Halves the number of chromosomes.

Remember before meiosis starts the chromosomes are copied during Interphase.

Haploid vs Diploid Haploid: cell that contains only one set of genes (n) Ex: gametes (egg and sperm) Diploid: cell that contains 2 sets of homologous chromosomes (2n) Ex: somatic cells (skin cells, bone cells)

Homologous: chromosomes in which one set comes from the male parent an one set come from the female parent

Example Haploid vs Diploid If chimp gamete has 24 chromosomes how many chromosomes does a chimp lung cell have?

Meiosis I Prophase I Chromosomes become visible. Nuclear envelope breaks down. Crossing over occurs. Crossing over- exchange of DNA between homologous chromosomes. (ex- eye color gene for eye color)

Metaphase I Pairs of homologous chromosomes move to equator of cell.

Anaphase I Homologous chromosomes move to opposite poles of cell

Telophase I & cytokinesis Chromosomes gather at the poles of the cells. Cytoplasm divides

Meiosis II Prophase II New spindle forms around chromosomes; nuclear envelope breaks down

Metaphase II Chromosomes line up on the equator

Anaphase II Centromeres divide. Chromatids move to opposite poles of cell.

Telophase II & cytokinesis Nuclear envelope forms around each set of chromosomes. Cytoplasm divides.

Fertilization: egg and sperm unite to create a diploid cell. Zygote: a fertilized egg.

Meiosis in males: makes 4 functional sperm cells Meiosis in males: makes 4 functional sperm cells. Called spermatogenesis Meiosis in females: only 1 of the 4 becomes a mature egg cell. The other 3 are called polar bodies and die. Called oogenesis