1. Check/Take up Homework

2. SExual reproduction continued
Spermatogenesis and Oogenesis

3. Cell division: a comparison
Mitosis
Meiosis
Function of Process
Genetic Variability
Number of Divisions
Number of Cells Produced
Number of Chromosomes Per Cell
to produce somatic cells
to produce sex cells
Yes - crossing over during
Prophase I
None
One
Two
Two
Four 46
Diploid 2n 23
Haploid n

4. gamete formation (Gametogenesis)
Meiosis takes place in the testes and ovaries (haploid sperm [n] and egg cells [n] respectively are produced)
Haploid gametes unite to form diploid (2n) zygote known as fertilization

5. oogenesis Begins with a diploid cell called an oogonium
Cytoplasm of female gametes doesn’t divide equally after nuclear division
One daughter cell receives most of the cytoplasm after the division. That cell continues through meiosis I and II to form ONE viable egg. This cell contains a large quantity of nutrients that will support a zygote after fertilization
The other 3 polar bodies die and the body absorbs the nutrients.
Begins with a diploid cell called an oogonium
Did you know.....
Before birth, the oogonia reproduce by mitosis, and they begin meiosis, but stop at prophase I. Meiosis I will continue for one cell each month beginning at puberty

6. Up to 1 billion sperm cells produced / day
spermatogenesis
Begins with diploid cell called spermatogonium
Equal division of cytoplasm with sperm
4 cells produced via meiosis
Capable of many mitotic divisions before meiosis
Up to 1 billion sperm cells produced / day

8. Sources of genetic variation
1. Crossing Over
2. Independent Assortment

9. Crossing over
In prophase 1, non-sister chromatids can exchange pieces of chromosomes
As a result, individual chromosomes can contain genes of maternal origin and some genes of paternal origin
Increases genetic diversity of the gametes produced

10. independent assortment
In metaphase 1, homologous chromosomes line up in the middle of the cell
Depending how the homologous chromosomes line up, a number of different combinations of chromosomes may be found in the gametes

11. Homework
Read pages
Pg. 181 # 1, 4, 6, 9, 11