1. Meiosis and Sexual Reproduction

2. Meiosis and Sexual Reproduction
First, some vocabulary:
chromosomes  Structures in the nucleus of a eukaryotic cell that consist of DNA molecules that contain the genes
alleles  Alternate forms of a gene.
homologous chromosomes are chromosomes that carry the same genes
example: if a gene influencing eye color is located at a particular place on one chromosome, then the homologous chromosome has a similar gene for eye color there.
gametes  Haploid reproductive cells (ovum and sperm).
genes  Specific segments of DNA that control cell structure and function; the functional units of inheritance.

3. Picture of chromosome and gene

4. Homologous Chromosomes
At this point, I would like you to complete the Problem-Solving Lab on page 270.
diploid  Cells that contain homologous chromosomes. The number of chromosomes in the cells is the diploid number and is equal to 2n (n is the number of homologous pairs).
haploid  Cells that contain only one member of each homologous pair of chromosomes (haploid number = n). At fertilization, two haploid gametes fuse to form a single cell with a diploid number of chromosomes.

5. Chromosome #’s of common organisms
Body cell (2n)
Gamete (n)
Fruit fly 8 4
Garden pea 14 7
Leopard frog 26 13
Human 46 23
Chimpanzee 48 24
Dog 78 39
Which # is haploid? Which # is diploid?

6. Meiosis
the process of nuclear division where the number of the chromosomes is halved.
produces four daughter cells
all daughter cells are haploid
chromosomes are shuffled in the process, so that each daughter cell has a unique combination
used to create gametes (sperm and egg)

7. Meiosis diagram

8. What is so special about meiosis?
It gives us genetic variability!! In other words, it is what makes you different from your siblings.
How does this happen?
Crossing Over - chromosomes exchange sections (increases variability)

9. When does crossing over occur?
Crossing over occurs during Prophase 1
Crossing over occurs here

10. Meiosis is sexual reproduction
Involves the fusion of gametes, creates unique offspring
- Eggs are much larger than sperm
Image of egg and sperm

11. Let’s see meiosis in action!!