1. Meiosis-Reduction Division
Ch. 9-5 and 9-6

2. Gametes Form from cell division of sex cells
Meiosis is cell division to produce gametes
Meiosis has two divisions of the nucleus (Meiosis I and Meiosis II) and produces cells with half the number of chromosomes (haploid)

3. Meiosis Reduces the genetic material by half Why is this necessary?
from mother
from father
child
too
much!
meiosis reduces genetic content

4. Homologous Chromosomes
Carry the same genes
Pair during Meiosis I
Separate in the formation of gametes
One copy of each pair is from the mother and one is from the father.
Figure 1.2

5. Sexual Reproduction
Meiosis and sexual reproduction increases genetic diversity in a population
Variation is important in a changing environment
Evolution is the genetic change in a population over time

6. Comparison of Mitosis and Meiosis
Table 3.1

7. Meiosis Interphase precedes meiosis I Meiosis I Prophase I Meiosis II
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Figure 2.13

8. Meiosis I : the reduction division
Prophase I
(diploid)
Metaphase I
Anaphase I
Telophase I
Nucleus
Spindle
fibers
Nuclear
envelope
Figure 3.4

9. Prophase I Late prophase Chromosomes condense Early prophase
Spindle forms
Nuclear envelope fragments
Early prophase
Homologs pair
Crossing over occurs
Figure 3.4

10. Recombination (crossing over)D E F a b c d e f a b c d e f
Occurs in prophase of meiosis I
Homologous chromosomes exchange genes
Generates diversity
Figure 3.5

11. Recombination (crossing over)
Exchange between homologs
Occurs in prophase I C C c c D D d d E E e e F F f f
Figure 3.5
Letters denote genes and case denotes alleles

12. Recombination (crossing over)
Creates chromosomes with new combinations of alleles for genes A to F D D d d E E e e F F f f
Figure 3.5

13. Metaphase I Homolog pairs align along the equator of the cell
Figure 3.4

14. Independent Assortment
The homolog of one chromosome can be inherited
with either homolog of a second chromosome.
Figure 3.6

15. Anaphase I Homologs separate and move to opposite poles
Sister chromatids remain attached at their centromeres
Figure 3.4

16. Telophase I Nuclear membrane reforms Spindle disappears
Cytokinesis divides cell
Figure 3.4

17. Meiosis II : like mitosis; sister chromatids separate
Prophase II
(haploid)
Metaphase II
Anaphase II
Telophase II
Four
nonidentical
haploid
daughter cells
Figure 3.4

18. Prophase II
Nuclear envelope fragments
Spindle forms
Figure 3.4

19. Metaphase II
Chromosomes align
along equator of cell
Figure 3.4

20. Anaphase II
Centromeres divide
Sister chromatids separate
Figure 3.4

21. Telophase II Nuclear envelopes reform Chromosomes decondense
Spindle disappears
Cytokinesis divides cells
Figure 3.4

22. Results of Meiosis Gametes Four haploid cells
Contain one copy of each chromosome and one allele of each gene
Each cell is unique
Figure 3.4

23. Meiosis: Cell Division in Two Parts
Haploid
Diploid
Meiosis I
(reduction
division)
Meiosis II
(equational
Figure 3.3
Result: one copy of each chromosome in a gamete.

24. Table 3.1