1. Genetics
Meiosis

2. Sexual Life Cycles
Alternation of meiosis and fertilization is common in most living organisms

3. Sexual Life Cycles of Humans

4. Meiosis diploid and haploid stages
Meiosis II
Meiosis I
diploid
Meiosis II
haploid
haploid

5. Meiosis I reduction division, separates homologues
Meiosis II
Meiosis I
diploid
Meiosis II
haploid
haploid

6. Meiosis I Interphase (precedes Meiosis) Meiosis I
G1 , S, G2
Meiosis I
prophase I, metaphase I, anaphase I, telophase I
Cytokinesis (follows Meiosis)

7. Interphase
precedes meiosis
G1 first gap
S synthesis
G2 second gap

8. Prophase I longest phase synapses tetrad formation crossing-over
chiasma

9. Metaphase I
tetrads align at the
metaphase plate

10. Anaphase I homologous chromosomes pull apart
separation accomplished by
disassembly of kinetochore
microtubules
elongation by nonkinetochore
homologous chromosomes
separate

11. Telophase I Chromosomes reach the poles each pole with haploid number
cleavage furrow

12. Cytokinesis Division of cytoplasm animal cells form a cleavage furrow
plant cells form a cell plate
cleavage furrow

13. Meiosis II mitotic division, separates sister chromatid
diploid
Meiosis II
haploid
haploid

14. Meiosis II prophase II, metaphase II, anaphase II, telophase II
Cytokinesis

15. Prophase II
spindle apparatus forms

16. Metaphase II
sister chromatids align at equator

17. Anaphase II
sister chromatids separate

18. Telophase II daughter cells contain half the number of chromosomes the
initial parent cell had
2n n
diploid haploid

19. vb v

20. Summary
ghgnfn

21. Gametogenesis
Spermatogenesis
Oogenesis

22. Spermatogenesis

23. Oogenesis
End product is ONE egg and 3
polar bodies

24. Some Zygote Possibilities
single birth
1 sperm + 1 ovum = 1 zygote
monozygotic (identical) twins
dizygotic (fraternal) twins
2 sperm + 2 ova = 2 zygotes

25. Events that contribute to Variations
independent assortment chromosomes
random fusion of gametes
crossing-over
mutations

26. Independent assortment of chromosomes

27. Random fusion of gametes
A gamete from one individual unites with a gamete from another individual
1 in 8 million x 1 in 8 million = 64 trillion
64 trillion combinations of chromosomes

28. Crossing-over
Prophase I

29. Chromosomes human = 46 chromosomes (23 pairs)
autosomal chromosomes = 44 (22 pairs)
sex chromosomes = 2 (1 pair)

30. Female Sex Chromosomes
female = XX
all gametes carry X chromosome
homogametic sex

31. Male Sex Chromosomes male = XY 1/2 of gametes carry X, 1/2 carry Y
heterogametic sex
Hemizygous

32. Activity Is this cell going through mitosis or meiosis?
How do you know?

33. Is this cell going through mitosis or meiosis? How do you know?
What specific stage is it in?
What special process is
going on?
What is the importance of it?
The End