1. Sexual Reproduction Parents: 2 Offspring: different
Cell division: MEIOSIS 46 23 23
MEIOSIS
Produces gametes:
SPERM and EGG 23 23 23 23

2. Why meiosis? FERTILIZATION: 23 + 23 = 46 EGG (haploid)
HALF the normal # of chromosomes
SPERM
(haploid)
HALF the normal # of chromosomes
ZYGOTE
(diploid)
normal # of chromosomes
(2 of each)

3. Meiosis PROS CONS Genetic variation The MOST IMPORTANT benefit!!!
Not as fast as asexual reproduction (can’t produce as many offspring)
Need to find a mate
PROS
Genetic variation
The MOST IMPORTANT
benefit!!!

4. Cells in your body have a chromosome set (all 46)- they are called diploid 
Gamete cells (sperm and eggs) only have half (23)  - they are called haploid

6. Genetic Variation in Meiosis
Recombination
Crossing Over
Homologous chromosomes switch pieces

7. Genetic Variation in Meiosis
INDEPENDENT ASSORTMENT
Homologous pairs of chromosomes are “sorted” differently each time a gamete is formed
Sperm from the same man and eggs from the same woman can have different combinations of genes because of this independent assortment!
Example:
What are the possible gametes that will be produced from this diploid cell?
HINT:
Each gamete will get one “S” and one “T”

8. 3 Sources of Genetic Variation in Meiosis
CROSSING
OVER (prophase I)
2. INDEPENDENT ASSORTMENT (metaphase I)
3. RANDOM FERTILIZATION

9. Mitosis
Includes only 1 cycle of cell division
Occurs in body cells (somatic cells)
No crossing over of chromosomes
Results in two genetically identical diploid cells
Metaphase: 1 duplicated chromosome per spindle fiber
Meiosis
Includes 2 cycles of cell division (meiosis I and meiosis II)
Occurs only in sex cells (gametes)
Chromosomes cross over in Prophase I
Results in four genetically different haploid cells
Metaphase I: 2 duplicated chromosomes per spindle fiber

11. Meiosis and Sexual Reproduction: Practice
Which of the following types of cells would experience mitosis, meiosis, or both? Write ME for meiosis, MI for mitosis.
____A pollen cell of a plant
____A leaf cell of a plant
____A root cell of a plant
____The cells in the petal of a flower
____Stem cells
____Kidney cells
____Liver cells
____Testes cells
____Ovary cells
____Tree bark cells