1. Section 11.4
Meiosis

2. A) Stages of Meiosis
Goal: 1. Final product will be 4 haploid (half the number of chromosomes) cells 2. Make gamete cells (egg and sperm cells)

3. Meiosis: 2 divisions Result: one copy of each chromosome in a gamete.
Sister
chromatids
separate
Haploid
Diploid
Meiosis I
(reduction
division)
Meiosis II
(equational
Homologs
separate
Result: one copy of each chromosome in a gamete.

4. A) Stages of Meiosis Interphase- G1-growth
S phase-replicate DNA (after this step the cell will have 96 chromosomes)
G2-growth

5. A) Stages of Meiosis
1) Meiosis I a) Prophase (same as Mitosis w/ extra) 2. Crossing over: exchange pieces of chromosome between mother and father chromosomes a) genetic recombination: mixing up genes

6. The two chromosomes connected make a tetrad.

7. a) Prophase I Chromosomes with the same characteristics pair.
Crossing over occurs.
Chromosomes condense.
Spindle forms.
Nuclear membrane disappears.

8. Recombination (crossing over)
Occurs in prophase of meiosis I
Generates diversity A a A a B b B b C C c c
Letters denote genes
Case denotes alleles
Creates chromosomes with new combinations of alleles for genes A to C.

9. b) Metaphase I
1. Chromosome pairs align
along the equator of the cell

10. c) Anaphase II
Chromosome pairs separate and
move to opposite poles.
Independent assortment: random separation of chromosome pairs = genetic recombination

11. Telophase I Nuclear membrane reassemble. Spindle fibers disappear.
Cytokinesis divides cell into two.
Result: 2 Genetically different cells with 46 chromosomes

12. Meiosis I :reduction division
Prophase I 96
Chromosomes
Metaphase I
Anaphase I
Telophase I 46
(Diploid)
Nucleus
Spindle
fibers
Nuclear
envelope

13. Prophase II
Nuclear membrane fragments.
Spindle fibers form.

14. Metaphase II
Chromosomes align
along equator of cell.

15. Anaphase II Chromatids separate and move to opposite poles.
This increases genetic diversity again.

16. Telophase II Nuclear membrane assembles. Spindle fibers disappears.
Cytokinesis divides cell into two.
Result: 4 genetically different cells with 23 chromosomes, Haploid Cells

17. A) Stages of Meiosis Results of Meiosis: 4 Haploid cells are created
Contains half the # of chromosomes as original cell
Genetic variation will increase chance of survival

18. Mitosis Meiosis Number of divisions 1 2 Number of daughter cells 4
Genetically identical?
Yes No
Chromosome #
Same as parent
Half of parent
When
Throughout life
At sexual maturity
Role
Growth and repair
Sexual reproduction

19. B) Formation of Gametes
Animal cell: meiosis occurs in reproductive organs
a) Female: Ovary Male: Testis

20. Sperm and Egg

22. Oogonium
(diploid)
Mitosis
Primary
oocyte
Meiosis I
Secondary
(haploid)
Meiosis II
(if fertilization
occurs)
First polar body
may divide
Polar
bodies
die
Ovum (egg)
Second
polar body a A X
Mature
egg

23. C) Asexual and Sexual Reproduction
Asexual Reproduction: reproduction of offspring from 1 parent
a) No genetic diversity
Sexual Reproduction: reproduction of offspring by a sex cell from each parent
a) Results with genetic diversity