Overview of MEIOSIS Meiosis is the process of making GAMETES. One of the most important things that happens during this process is called CROSSING OVER, where two pieces of DNA exchange parts, this is what leads to us looking different from our brothers and sisters (Genetic recombination). During Meiosis we take body cells that have HOMOLOGOUS CHROMOSOMES in them and we break them apart twice so that we end up with a chromatid in each GAMETE. Essentially MEIOSIS is MITSOSIS times two, and the wording for MEIOSIS 2 is the exact same as MITOSIS

Review What are the 2 types of reproduction What are Chromatid, sister chromatids? List the stages of mitosis Is interphase a stage of mitosis? Explain your answer What is an allele?

CELL DIVISION: WHY DOES IT HAPPEN? Three essential life processes –3) Reproduction 2 TYPES ASEXUALSEXUAL AKA BINARY FISSION 1) Offspring produced by one parent by two parents 2) Daughter cells are Identical combo of both parents 3) Requires MITOSIS 3) Requires MEIOSIS

MEIOSIS: Dip to Hap Diploid (2n): 2 sets of complete Chromosomes (1 from ma & 1 from pa)

MEIOSIS: Dip to Hap Haploid (n) = one complete set of chromosomes (either one from ma (egg) OR one from pa (sperm))

Dip and Hap Numbers DipHap Humans Dogs Tomato Orange 30 ? Grape ? 20

Homologous Pairs: The Buddy System Homologous pairs: A similar pair of chromosomes, one from the mother & one from the father

Homologous Pairs: The Buddy System Homologous pairs: A similar pair of chromosomes, one from the mother & one from the father

Tetrad: homo Chromo from mom and dad What is a Tetrad? A set of chromosomes from mom and dad that will eventually separate into 4 different cells

MEIOSIS I Prophase 1 Metaphase 1 Anaphase 1 Telophase 1

Crossing Over: For a Change What is crossing over? The exchange of pieces of chromosomes between two non sister chromatids (one chromosome from mom and one from dad)

Crossing Over: For a Change Why does crossing over happen? So we can have genetic variation in a population and species When does it happen? –Prophase 1

Meiosis I Everything is the same as MITOSIS BUT instead of Chromatids separating HOMOLOGOUS CHROMOSOMES are separating.

MEIOSIS II: Doin’ it again This is really just mitosis all over again (so study Mitosis Notes) In the end we get 4 cells

Meiosis II: Naming the phases Prophase II Metaphase II Anaphase II Telophase II Meiosis II chromatids separate –(Just like Mitosis)

Review What is haploid? What is diploid? What is the haploid number of human gametes (sex cells, sperm,egg)? What is the diploid number for humans? When do homologous chromosomes separate? (What phase) How many haploid daughter cells are produced after the completion of Meiosis?