1. Sexual Reproduction Meiosis

2. Where do we get our characteristics from?
How does our body know which traits to reflect?
Where is this information located?
How is this information arranged?
Genes control the production of proteins
Each chromosomes has hundreds
Parents. (we’ll learn later there are other things—our environment—involved)
Give me some examples of characteristics/traits.
In chromosomes, yes, but more specifically in genes!

3. Chromosomes Human body cells have 46 chromosomes
Each parent contributes 23 chromosomes resulting in 23 pairs of chromosomes – called homologous chromosomes
In order to maintain the same number of chromosomes from generation to generation, an organism produces gametes.
Sex cells that contain half the number of chromosomes
Varies between species.
Homologous meaning they’re matched – earlobe example!
So how many?

4. Chromosomes
We use the symbol n to represent the number of chromosomes in a gamete.
n – haploid
2n – diploid
Two haploid (n) gametes combine via fertilization to make a cell with 2n chromosomes.
Each parent contributes a gamete (x or y)
Female XX (egg), Male XY (sperm)
Relate to mitosis
Polar bodies – when an egg is produced and the cells divide unevenly

5. Oogenesis

6. Meiosis Gametes (n) are formed via meiosis. Meiosis I and Meiosis II
Meiosis occurs in the reproductive structures of organisms that reproduce sexually.
Reduces the chromosome number by half
Meiosis I and Meiosis II
Sperm and egg!
Mention germ/sex v. somatic/body
Mitosis maintains the chromosome number

8. Interphase and Prophase I
Interphase is the same as mitosis
As homologous chromosomes condense, they begin to form pairs via synapsis.
Crossing over – chromosomal segments are exchanged between a pair of homologous chromosomes.
What does interphase do? Similar stuff is occurring throughout…
Chromosomes are held tightly
Crossing over – go back a slide. This is what gives us variation!!!

9. Metaphase I
Pairs of homologous chromosomes line up at the center of the cell
Spindle fibers attach to the centromeres
Pairs lineup, not the individual chromosomes!

10. Anaphase 1 Homologous chromosomes separate
Each still consists of two sister chromatids
Chromosome number has reduced from 2n to n
Please note, sister chromatids may not be identical bc of crossing over!

11. Telophase I and Cytokinesis
The homologous chromosomes that consist of two sister chromatids reach the cell’s opposite poles.

14. Meiosis II Much of the same – very similar to mitosis. Cytokinesis
Spindle fibers form, centromere
Chromosomes line up at center (haploid n)
Move to opposite poles
Cytokinesis
Result: four haploid (n) cells that are not identical
Why? Because of crossing over. This provides variation.

16. See figure 10-5 in your text!

17. Sexual v. Asexual Reproduction
Some organisms reproduce sexually, whereas others reproduce asexually
Sometimes life cycles include both forms (protists and plants)
Asexual – offspring are identical to parent (bacteria)
Asexual - think mitosis. Plants different parts of life cycle!
What would be the advantages and disadvantages?

18. In groups of 3, construct a venn diagram comparing mitosis and meiosis
In groups of 3, construct a venn diagram comparing mitosis and meiosis. Consider the following:
What each starts with
What each ends with
Steps to get there (stages)
Type of cell
Number of divisions
Different steps (i.e. crossing over/cleavage)
Anything else you might find useful…