Meiosis “Reduction Division”

Reduce the number of chromosomes by half Produce haploid cells (1 set of chromosomes) 2N → N Produce gametes (egg or sperm) Allows for genetic variation

Meiosis I - Stages Interphase – replication occurs Produce additional DNA for the new cells Parent Cell - Initially 2N = ? Then N = ?

Meiosis Stages: Prophase I How is this different from prophase of mitosis? Homologous chromosomes pair up Chromosomes appear as tetrads Synapsis occurs

Meiosis Stages: Metaphase I How is this different from metaphase of mitosis? Tetrads (homologous pairs) line up at the equator

Meiosis Stages: Anaphase I How is this different from anaphase of mitosis? Tetrads separate Chromosomes move to the poles How many “N” is the cell? Still 2N unlike mitosis

Meiosis Stages: Telophase I How many cells are produced? 2 cells Are the cells diploid or haploid? haploid How do you know the process is not done? Chromatids still present __________________

Meiosis II is a Mitotic Process Copying the cells from Meiosis I Is replication necessary? No—chromosomes are already duplicated Stages used to organize chromosomes to ensure an equal distribution Sequence is Prophase II, Metaphase II, Anaphase II & Telophase II End with 4 haploid cells (two of each type)

__________________________ _ End of Meiosis I End of Meiosis II Are these the only cells possible? Diagram the other possible set.

And Other possible set What determines which set is formed ? Chance –how the chromosomes line up during Metaphase I Increases probability of variation

Crossing Over Occurs during meiosis I Exchange of genetic material Increases variation Can be a cause of mutations