1. 5c. Meiosis
Chapter 6.1 & 6.2

2. You have body cells and gametes.
Body cells are also called somatic cells.
Example: blood, skin, nerve cells
Gametes are your sex cells (eggs and sperm)
Germ cells (which are somatic) develop into gametes
Germ cells divide into sex cells
Germ cells are located in the ovaries and testes.
Gametes have DNA that can be passed to offspring.
body cells
sex cells (sperm)
sex cells (egg)

3. Your cells have autosomes and sex chromosomes.
Your body cells have 23 pairs of chromosomes.
Homologous pairs of chromosomes have the same structure.
For each homologous pair, one chromosome comes from each parent.
Chromosome pairs 1-22 are autosomes.
Sex chromosomes, X and Y, determine gender in mammals.

4. Body cells are diploid; gametes are haploid.
Fertilization between egg and sperm occurs in sexual reproduction.
Diploid (2n) cells have two copies of every chromosome. (one from mom, one from dad)
Body cells are diploid. (pair of X-somes)
Half the chromosomes come from each parent.

5. Haploid (n) cells have one copy of every chromosome.
Gametes are haploid.
Gametes have 22 autosomes and 1 sex chromosome.
Only Eggs and Sperm are haploid (only have 1 “shoe”)

6. Comparing Mitosis and Meiosis
Mitosis and meiosis are types of nuclear division that make different types of cells.
Mitosis makes more diploid cells. (somatic cells)
Meiosis makes haploid cells (gametes)
Mitosis produce identical cells
Meiosis produce genetically unique cells
Mitosis produces diploid cells
Meiosis produces haploid cells

7. Cells go through two rounds of division in meiosis.
Meiosis reduces chromosome number and creates genetic diversity.

8. Meiosis I and meiosis II each have four phases, similar to those in mitosis.
Goes through the phases of mitosis twice
Meiosis 1 and Meiosis 2
Biggest difference is Prophase 1
Homologous chromosomes partner up to form a tetrad.
Crossing over occurs (chromosomes trade DNA)

9. Crossing Over is what leads to genetic diversity

10. Meiosis I occurs after DNA has been replicated. (S phase)
Meiosis I divides homologous chromosomes in four phases.

11. Meiosis II divides sister chromatids in four phases.
DNA is not replicated between meiosis I and meiosis II.

12. Haploid cells develop into mature gametes.
Gametogenesis is the production of gametes.
Gametogenesis differs between females and males.
Spermatogenesis is the making of sperm
4 viable sperm are produced
Oogenesis is the making of eggs
Makes 1 viable egg & 3 Polar Bodies