1. Ch. 7 Meiosis & Sexual Reproduction

2. What if…
What if…
A HUMAN sperm & egg each had 46 chromosomes, like other human body cells, how many chromosomes would a zygote have?
Why might an increase in the number of chromosomes a human cell has cause problems?

3. WHITEBOARDS Draw the gametes for males and females
Inside each sex cell, give the number of chromosomes
Below your drawing, write whether the sex cells are haploid or diploid
If an organism’s sex cells have 12 chromosomes, how chromosomes will a body cell have?

4. Meiosis- Formation of Haploid Cells
1. DNA in the original cell replicated
2. Meiosis halves the number of chromosomes when forming gametes or spores
Still occurs in the nucleus!
Start out with diploid cell, replicate DNA – chromosomes are cut in half

5. Draw it out!
Meiosis
Look at your books (p. 144) and your notes for pictures of Meiosis I & II
Draw your assigned stage on the board – be ready to explain it!
Start out with diploid cell, replicate DNA – chromosomes are cut in half

6. Meiosis I
Meiosis
Start out with diploid cell, replicate DNA – chromosomes are cut in half

7. Meiosis II
Meiosis
Start out with diploid cell, replicate DNA – chromosomes are cut in half

8. Hold them up!
Meiosis
Hold up the number of cells produced at the end of Meiosis I
Hold up the number of cells produced at the end of Meiosis II
Hold up the number of sets of chromosomes in one haploid cell at the end of Meiosis II
2 Sets = 46 chromosomes
1 Set = 23 chromosomes

9. Meiosis- Formation of Haploid Cells
4 haploid cells result at the end of Meiosis II

10. Think – Pair - Share Genetic Variation
What does the term “genetic variation” mean?
How important is genetic variation to the survival of our species?

11. Importance of Genetic Variation
1. Meiosis and the joining of gametes are essential to evolution
No genetic process generates variation more quickly
2. Evolution appears to increase with increases in genetic variation

12. Meiosis & Genetic Variation
1. Independent Assortment-
In humans, each gamete receives 1 chromosome from each of 23 pairs of homologous chromosomes ( = 23 total chromosomes = 1n)
Which of the 2 homologues each offspring receives is a matter of chance
8 million different gamete combinations can result

13. Meiosis & Genetic Variation
2. Crossing Over-
DNA exchange during Prophase I in Meiosis
Portions of a chromatid on 1 homologous chromosome are broken & exchanged with the chromatid portions of the other homologous chromosome

14. This recombination GREATLY increases genetic variation
-How is this different from translocation?
-Crossing over occurs between homologous
chromosomes
-Translocation is with non-homologous

15. Meiosis & Genetic Variation
3. Random Fertilization- two gametes are randomly joined to form a zygote
64 trillion possible outcomes

16. Genetic Variation - Importance
Importance of genetic variation
Breeding larger or faster animals can be limited until enough genetic variation is eventually generated to continue the breeding

17. Genetic Variation Importance
Importance of genetic variation
4. Natural selection doesn’t always favor genetic change
Existing conditions may be favorable, slowing evolution

18. Meiosis- Formation of Haploid Cells
Pages 148 – 149
Boys do Spermatogensis
Girls do Oogenisis

19. Meiosis- Formation of Haploid Cells
Meiosis in Males
SPERMATOGENESIS- produce sperm in the testes of male animals
A. Diploid cell increases in size to germ cell
B. Undergoes meiosis I
C. Undergoes meiosis II to form 4 haploid cells
D. 4 cells develop tail (sperm)

20. Meiosis- Gamete Production
Meiosis in females
OOGENESIS- produces eggs in the ovary of female animals
A. Diploid cell increases in size to a germ cell
B. Undergoes meiosis I- cytoplasm splits unevenly into each egg cell
C. Undergoes meiosis II- more uneven cytoplasm distribution
D. One large egg cell develops, 3 polar bodies that do not survive

22. Meiosis vs. Mitosis Meiosis vs. Mitosis Mitosis – Meiosis –
Division of somatic (body) cells
Diploid (2n)
Creates identical cells
Meiosis –
Division of chromosomes to form reproductive cells
Haploid (n) sex cells produced
Genetic variation

23. Sexual Life Cycles in Eukaryotes
Entire span in the life of an organism from one generation to the next

24. Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
1. Zygote is diploid but undergoes meiosis immediately to make new haploid cells (any DNA damage is repaired)

25. Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
2. Haploid cells create haploid individuals
3. Gametes are produced by mitosis

26. Sexual Life Cycles in Eukaryotes
Sexual Haploid Life Cycle
4. Gametes fuse to produce diploid zygote, cycle continues
Occurs in protists, fungi, algae, chlamydomonas

27. Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
1. Adults are diploid, each inheriting characteristics from both parents
2. Diploid reproductive cells undergo meiosis to produce gametes

28. Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
3. Fertilization- joining of gametes (sperm and egg)
4. Resulting zygote divides by mitosis

29. Sexual Life Cycles in Eukaryotes
Sexual Diploid Life Cycle
5. Cells of adult also end up diploid
6. All cells involved are diploid, except gametes which are haploid
Ex: Humans/ Animals

31. Sexual Life Cycles in Eukaryotes
Alternation of generations
1. Often in plants, alternates between haploid and diploid phases

32. Sexual Life Cycles in Eukaryotes
Alternation of generations
2. Sporophyte- diploid phase in plant life cycle that produces spores
Spore forming cells undergo meiosis to produce spores (haploid reproductive cell that become an adult without fusing with another cell)

33. Sexual Life Cycles in Eukaryotes
Alternation of generations
3. Gametophyte- haploid phase in plant life cycle that produces gametes through mitosis
Gametes fuse and give rise to diploid phase

34. Sexual Life Cycles in Eukaryotes
Alternation of generations
4. Ex: Moss
Stalk tip’s capsule pops off scattering haploid spores
Spores germinate by mitosis and form gametophytes
Male gametophyte releases sperm that swim through film of moisture to eggs in female gametophyte
Diploid zygote develops as sporophyte within the gametophyte
Cycle continues

36. Cloning by parthenogenesis
1. A new individual develops form an unfertilized egg
2. No male involved, offspring is genetic clone of mother
3. Mother’s own chromosomes are copied in place of the male’s
4. Occurred in females without male companionship for long periods of time
5. Dandelions, hawkweeds, fish, lizards, frogs, snakes, male drone honeybees, NO MAMMALS

38. Research in
Parthenogenesis

39. Assessment
Identify the type of reproduction that results in offspring that are genetically identical to their parent
Describe two different types of eukaryotic asexual reproduction
Compare the haploid life cycle found in chlamydomonas with a diploid life cycle
Summarize the process of alternation of generations
Evaluate the significance of mutations and repair of mutations to the evolution of sexual reproduction