1. Meiosis
Chapter 10.1

2. Cell reproduction review
Cell cycle
Interphase – DNA replicated
Mitosis – nuclear division
Cytokinesis – cytoplasm divided
Results in 2 cells that are exact copies of the original cell.

3. Sexual Reproduction Humans and other animals reproduce sexually
Two specialized cells form to make a new organism.
Gametes or sex cells
Human gametes: eggs and sperm

4. Chromosomes Humans have 46 chromosomes
Each parent contributes 23 chromosomes
Homologous chromosomes: Two paired chromosomes, one from each parent
23 sets of homologous chromosomes

5. Haploid and Diploid Cells
Haploid – (N) number chromosomes
Diploid – (2N) number chromosomes
Gametes are haploid
Gametes maintain the same number of chromosomes from generation to generation

6. Sexual Reproduction Cell Cycle
Interphase
Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II

7. Meiosis
Cell division to make four gametes with half the number of chromosomes
Two divisions : Meiosis I and Meiosis II
Male: Spermatogenesis
Female: Oogenesis

8. Interphase Chromosomes replicate
Each duplicated chromosome consists of two identical sister chromatids attached at centromeres.

9. Meiosis I (four phases)
Cell division that reduces the chromosome number by one-half. (Diploid  haploid)
four phases:
a. prophase I
b. metaphase I
c. anaphase I
d. telophase I

10. Prophase I – Meiosis I Chromosomes condense
Synapsis – Homologous chromosomes come together to form a tetrad.
Crossing over occurs (variation)

11. Prophase I – Crossing over
Segments of non-sister chromatids break and reattach to the other chromatid
Chiasmata – site of crossing over

12. Prophase I

13. Metaphase I Tetrads align on the metaphase plate
Independent assortment occurs – orientation of homologous chromosomes is random.
Creates variation

14. Metaphase I

15. Anaphase I Homologous Chromosomes separate
Sister chromatids remain attached at centromere.

16. Telophase I Homologous chromosomes reach the poles
The poles have haploid set of chromosomes
Cytokinesis – cytoplasm splits. Two haploid daughter cells are made.

17. Telophase I
Cytokinesis

18. Meiosis I Overview
Meiosis I Summary

19. Meiosis II No interphase II (or very short - no more DNA replication)
Remember: Meiosis II is similar to mitosis
four phases:
a. prophase II
b. metaphase II
c. anaphase II
d. telophase II

20. Meiosis II No Interphase – no replication
Meiosis II is very similar to mitosis

21. Prophase II Chromosomes condense Nucleus disappears
Spindle fibers form & attach again

22. Metaphase II
Chromosomes line up on metaphase plate

23. Anaphase II
Sister chromatids separate

24. Telophase II Chromosomes arrive at poles Nucleus reforms
Cytokinesis occurs – produces 4 haploid daughter cells

25. Telophase II
Cytokinesis

26. Oogenesis
Female – begins before birth until menopause

27. Spermatogenesis
Male – begins at puberty continues until death

28. Meiosis Overview
VIDEO

29. Karyotype
A method of organizing the chromosomes of a cell in relation to number, size, and type.
SKIP

30. Fertilization Fusion of Egg and sperm to form a Zygote. Egg – haploid
Sperm – haploid
Zygote – diploid

31. Genetic variation Meiosis creates variation within a population
1) Crossing over (prophase I)
2) Independent assortment (Metaphase I)
3) Random fertilization
Variation allows for natural selection and evolution to occur