1. Meiosis
End ch. 8

3. Haploid Cells
In animals, meiosis produces gametes which are haploid reproductive cells
Haploid cells contain only one set of chromosomes
they have half the number of chromosomes present in diploid cells (somatic cells)
23 total

4. Diploid Cells Have full number of chromosomes
They are represented by 2n because they have 2 sets of chromosomes
Somatic Cells (not sex cells)

5. So Sex Cells Are: Haploid/Diploid

6. Sex Cells are Haploid Because:
½ DNA from mother (egg)
½ DNA from father (sperm)
So you can’t already have all of the DNA when the egg and sperm meet!

7. Differences in Meiosis vs. Mitosis

9. Prophase I Synapsis- the pairing of homologous chromosomes
chromatids of homologous chromosomes are aligned so the genes of one chromosomes are adjacent to the same genes on the other chromosome
Crossing-over – parts of chromatids break off and attach to adjacent chromatids on the homologous chromosome
Results in genetic recombination

10. Genetic Recombination
Because a new mixture of genetic material is created for the daughter cells (as a result of crossing-over) we call this genetic recombination
We are mixing up the genes! This is why all babies don’t look exactly like their parents!

12. Anaphase I
Independent Assortment- the random separation of the homologous chromosomes
all of mother’s chromosomes will not be separated into one cell
Instead, after meiosis occurs, each haploid cell contains a mixture of genes from the organism's mother and father.
Independent assortment results in genetic variation

14. Telophase I and Cytokinesis I
The new cells (2) contain a haploid number of chromosomes
Each new cell contains 2 copies (as chromatids) because the original cell copied its DNA before meiosis I

16. How Many Daughter Cells Do We End Up With At The End of Meiosis?4

17. And the New Daughter Cells Are Haploid/Diploid?

18. Mitosis vs. Meiosis

19. Development of Sex Cells (Gametes)
In animals the only cells that divide by meiosis are those that produce gametes within reproductive organs
Males = sperm
Females = eggs

20. Males = Spermatogenesis
The production of sperm cells
Produces 4 sperm cells
Occurs in testes

21. Females = Oogenesis The production of mature egg cells
Produces only 1 mature egg, other three are useless polar bodies
Occurs in ovaries

23. Sexual Reproduction

24. Sexual Reproduction
Sexual reproduction- the production of offspring through meiosis and the union of a sperm and an egg
Offspring are different from parents due to genetic recombination
Evolutionary advantage because allows species to develop new traits in a population