1. Draw and label a cell with: 2 pairs of homologous chromosomes
Each chromosome is attached to its sister chromatid
Draw and label the 2 daughter cells produced from this cell by mitosis

3. A special case of cell division
Meiosis
A special case of cell division

4. Mendel’s “Factors”
Characteristics of parents are transferred to offspring through DNA (packaged in cells as chromosomes)

5. Genome -
Chromosome -
Gene -

7. Your cells have 23 pairs of chromosomes: 1 - 22 plus X from Mom 1 - 22 plus X or Y from Dad
TOTAL = 46 chromosomes
Are you XX or XY?

8. Diploid = Cells with 2 copies of each chromosome (2N)
Homologous chromosomes = carry the same genes (but may have different alleles for the trait because each is from a different parent: Aa)

9. Diploid Human ChromosomesT O S M E

10. Answer this!
How are homologous chromosomes the same? How are they different?
What is the difference between autosomes vs. sex chromosomes?
homologous chromosomes vs. sister chromatids
Somatic (body) cell vs. Gamete cell

11. Problem: If diploid cells from parents simply
combine at fertilization to make offspring (that’s you),
the chromosome number would double with each generation
46  92  184  etc.
Why doesn’t that happen?

12. Diploid organisms produce specialized cells for reproduction
Gamete cells = eggs and sperm
Gamete cells have only ONE copy of each chromosome pair
Haploid - one copy of each chromosome in cell (N)

13. Answer this!
Explain the difference between a diploid cell and a haploid cell.
If a chimpanzee has 48 chromosomes in body cells, how many chromosomes are in chimpanzee gametes (eggs or sperm)?

14. Meiosis Produces haploid cells with unpaired chromosomes
Used only to make eggs and sperm (gametes)
Occurs only in reproductive organs
Ensures variability in offspring

15. Daughter cells: Haploid (1N - 1 copy of each chromosome)
Have unique combinations of chromosomes
Do not have homologous pairs
4 produced with each round of meiosis
ARE NOT IDENTICAL TO PARENT!

16. Remember: DNA must replicate during “S” phase of cell cycle
Each chromosome is attached to sister chromatid at centromere
Sister chromatids separate in meiosis II.

17. Answer this:
What is the difference between homologous chromosomes and sister chromatids?
Which are produced during the “S” phase of the cell cycle?
What is a centromere?

18. 2 Divisions of Meiosis Meoisis 1
Homologs separate into 2 daughter cells
Each cell gets 1 homolog (1 copy of each chromosome)
Sister chromatids are still attached at centromere.

19. Meiosis II Sister chromatids separate into 2 daughter cells
Each cell is haploid (1N)
2 X 2 = 4 cells

22. Stages of meiosis are similar to mitosis
Prophase – chromosomes pair up
Metaphase – chromsomes line up
Anaphase – chromosomes separate
Telophase – chromosomes re-group at opposite sides of the cell

23. 2 Types of Cell Division have Different Goals!!!!!!
Mitosis
Meiosis
 2 cells
Daughter identical to original cell
Diploid
Growth & Repair
MOST CELL DIVISION IS MITOSIS
 4 cells
Daughter cells NOT like original cell
Haploid
Reproduction ONLY
Eggs & Sperm ONLY

24. Answer this! Which type of cell division produces growth?
How are the cells produced in meiosis different from the cells produced in mitosis?
Explain why meiosis is called a “reduction division” – what is reduced? (and why is this necessary?)

28. Key points of Meiosis  4 daughter cells Daughter cells are haploid
Daughter cells have unique combinations of chromosomes
Daughter cells do not have homologous pairs
Meiosis creates gametes (sperm and eggs)
Meiosis ensures variability in offspring

29. Answer this:
If a cell with 6 chromosomes (total)divides to form gametes, how many chromosomes will the resulting gametes each have?

30. Independent Assortment
Depending on how the chromosomes arrange during metaphase I, the cells formed can have a variety of different chromosome combinations.

31. Why go to all this trouble?
Variability! – Meiosis mixes up chromosomes in the gametes:
You can have any combination of chromosomes 1 – 22
Your gametes, 1 possible combination:
1,2,3,4,5,6,7,8,9,10,11,12,13,14, 15,16,17,18,19,20,21,22

32. Variety is the spice of life!
223 possible combinations just by independent assortment of chromosomes
> > > 8,388,608
Duggar Family

33. Mix it up even more!
Additional variation occurs by crossing over between chromosomes
Homologous chromosomes can switch pieces during prophase I.
This adds to the variability of the gametes formed.

34. Crossing Over During Prophase I: Chromosomes partner to form tetrads
Arms cross over
Pieces break off and re-attach to other chromosome
Result: Unique! New! Assortment of traits

35. Answer this:
Explain two ways meiosis produces daughter cells that have different combinations of genes from each other.
Why is variation important for evolution to occur?

36. Meiosis Hoedown

37. Meiosis Now do the meiosis hoedown!