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

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

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

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

10. Prophase I

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

12. Metaphase I

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

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

15. Telophase I
Cytokinesis

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

17. Prophase II
Chromosomes condense
Nucleus disappears

18. Metaphase II
Chromosomes line up on metaphase plate

19. Anaphase II
Sister chromatids separate

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

21. Telophase II

22. Spermatogenesis
Male – begins at puberty continues until death

23. Oogenesis
Female – begins before birth until menopause

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

25. 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