12/8/13 Objective: How does meiosis contribute to genetic variation? Do Now: -Take out your notes, online lab, and cancer activity from Friday.

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Presentation transcript:

12/8/13 Objective: How does meiosis contribute to genetic variation? Do Now: -Take out your notes, online lab, and cancer activity from Friday

Produces sex cells (egg and sperm) Produces 4 cells with HALF the normal chromosome number How many chromosomes do human body cells have? How many chromosomes do human sex cells have? (egg and sperm) How the heck does that happen?????

Gametes= sex cells that have HALF the normal number of chromosomes (human= 23) Somatic Cells= body cells that have full set of chromosomes (human = 46)

-Haploid (n): a cell with half the normal number of chromosomes (gametes) -Diploid (2n): a cell with full set of chromosomes (somatic cell)

Karyotype Sex Chromosomes: 23 rd Pair: XX = female XY= male

Homologous Chromosomes Same chromosome, one is from mom, one is from dad

Downs Syndrome

Turners Syndrome

Prophase I: - Spindle forms, chromosomes condense nuclear membrane disappears -Homologous chromosomes stick together forming 4 chromatids (tetrads)

Genetic Variation Crossing Over: occurs during Prophase I where homologous chromosomes exchange pieces.

Metaphase I: Tetrads (Homologous chromosomes) line up at the middle

Anaphase I: Homologous chromosomes separate and move to poles

Telophase I: 2 daughter cells are formed (chromosomes are still duplicated)

Prophase II: Spindle forms in daughter cells, nuclear membrane breakdown

Metaphase 2: Sister chromatids line up in the middle of cell

Anaphase II: Sister chromatids separate and move to poles

Telophase II: Cells split producing 4 haploid daughter cells that are ALL GENETICALLY DIFFERENT!

Genetic Variation Crossing Over: occurs during Prophase I where homologous chromosomes exchange pieces.

Meiosis Sour Straws 1. Maternal and Paternal Homologous Chromosomes

Meiosis Sour Straws

2. Crossing Over – Chromosomes exchange sections of DNA

Meiosis Sour Straws 2. Crossing Over – Chromosomes exchange sections of DNA

Meiosis Sour Straws 3. Meiosis I: Homologous Chromosomes separate

Meiosis Sour Straws 4. Sister chromatids separate to form four unique gametes

Meiosis Sour Straws