Meiosis Overview

Sexual Reproduction Defined: Gametes from two separate parents unite Meiosis: Diploid (2n) to haploid (n) cells Mechanism that allows for genetic diversity Many eukaryotes reproduce in this manner – Plants, animals and fungi

Meiosis: Prophase I Prophase I- chromosomes become visible and nuclear membrane breaks down. Crossing over occurs portions of one sister chromatid are broken and exchanged with portions of the corresponding chromatid of homologous chromosome.

Meiosis: Metaphase I Homologous chromosomes move to the middle of the cell and stay together.

Meiosis: Anaphase I The homologous chromosomes are pulled apart to opposite sides of the cell via spindle fibers. Notice that the sister chromatids are still linked together at the centromere.

Meiosis: Telophase I/ Cytokinesis A nuclear membrane reforms around the separated chromosomes Two new __________ diploid cells are formed

Meiosis II: Prophase II The nuclear membrane dissolves around the chromosomes

Meiosis II: Metaphase II Chromosomes line up in the middle of the cell and spindle fibers attach to sister chromatids’ centromeres

Meiosis II: Anaphase II The sister chromatids are pulled to opposite sides of the pole by the spindle fibers.

Meiosis II: Telophase II The nuclear envelope forms around each set of chromosomes Four unique haploid (1n) cells are formed

Genetic Variation Created ____________ ____________: the random distribution of homologous chromosomes Each of the 23 pairs of chromosomes separate independently of each other Thus, 2 23 (over 8 million) gametes can be produced by a single cell Gamete formation endless possibilities 2 23 x 2 23 = over 64 trillion unique zygotes Extremely important to the evolution of all species.

Meiosis Males Spermatogenesis: sperm production Females Oogenesis: egg (ova) production

Fertilization Gametes of opposite sexes join to make a diploid (2n) zygote Zygote: cell resulting from the fusion of gametes