1. Meiosis and Sexual Reproduction Notes
To be used with Meiosis and Sexual Reproduction Guided Notes

2. From poppa
From momma

3. Gametogenesis Gametogenesis: the formation of gametes (eggs and sperm)
Each species has a characteristic number of chromosomes
Homologous Chromosomes: the two members of a pair of chromosomes
contain genes for the same traits

4. Diploid vs. Haploid
Diploid Number: the number of chromosomes found in all body cells (2n)
Haploid Number: 1/2 the diploid number of chromosomes (n)
found in the egg and sperm cells of a species
DIPLOID
HAPLOID

5. Gametogenesis Terms Gametes: eggs or sperm
Gonads: specialized organs in higher animals where the gametes are made
Ovaries: female gonads
Testes: male gonads

6. Meiosis
Meiosis: process which involves a 1/2 reduction division of the chromosome number
Haploid nuclei are formed which contain only one chromosome of the original pair
Meiosis ONLY occurs in the gamete producing cells of the gonads (testes and ovaries)
The production of sex cells

7. First Meiotic Division- Interpahse1
DNA and chromosomes replicate

8. Prophase 1
Each chromosomes pairs with its matching homologous chromosome forming a tetrad
Crossing-over occurs here

9. Metaphase 1
Spindle fibers attach to the homologous chromosomes

10. Anaphase 1
Spindle fibers pull homologous chromosomes to opposite ends of the cell

11. Telophase 1 Nuclear membrane forms.
Cytokinesis occurs forming 2 new daughter cells having half the # of chromosomes.

13. Meiosis Terms Synapsis: the meeting of two homologous chromosome pairs
Tetrads: the two pairs of homologous chromosomes
Crossing Over: the exchange of chromosome pieces in the tetrad during crossing over
Crossing over increases the variability of the offspring
This is why the offspring of sexual reproduction show many variations

14. Crossing Over

15. Meiosis 2- Very similar to Mitosis

16. Prophase 2
Nuclear membrane disappears and spindle fibers form

17. Metaphase 2
Chromosomes line up in the middle

18. Anaphase 2
Chromosomes are divided in half (centromere is split)

19. Telophase 2 Cells divide in half again (cytokinesis)
Produced 4 haploid (n) daughter cells

22. Meiosis, continued
Disjunction: Homologous pairs of chromosomes separate and move toward opposite poles of the cell
Nondisjunction: the failure of homologous chromosomes to separate

23. Nondisjunction

24. Nondisjunction
Down's syndrome: results from the nondisjunction of chromosome 21
individual has an extra 21st chromosome
polyploidy: having an entire extra set of chromosomes
Will result in the 3n or 4n number of chromosomes

25. Down’s Syndrome Rates

26. Cyclopia Nondisjunciton of chromosome 13-15 or 17-18
Two eyes within one orbit
Proboscis-like appendage above the eye
Low-set or missing ears
Missing facial bones
Congenital heart disease
(do not survive)

27. Turner’s syndrome XO sex chromosomes 1/2000 female births
Short stature
Wide-spaced underdeveloped nipples
Webbed neck
Swelling of hands & feet
Sterile

28. Klinefelter’s Syndrome
XXY sex chromosomes
1/ male births
Greatly reduced male genitalia
No sperm production & no sex drive
Some breast production
Wide curvy hips

29. Jacob’s Syndrome XYY sex chromosomes 1/1000 male births
Taller than average
Normal to subnormal intelligence
Worse than normal acne
Dense body hair
(2% of maximum security prison population)

30. Superwoman Syndrome XXX sex chromosomes 1/2000 female births
Normal to slightly retarded intelligence
Extra development of female secondary sex characteristics
Fertile

31. Polyploidy

33. Meiosis and Fertilization
Meiosis and fertilization are necessary for sexual reproduction
Egg (n) + Sperm (n) =Zygote (2n)

34. Spermatogenesis Spermatogenesis: The production of sperm
one successful meiotic division produces 4 sperm

35. Sperm
Sperm Structure: smaller than the egg but capable of locomotion with its flagellum.

36. Oogenesis Oogenesis: the production of ova (eggs)
One meiotic division produces 1 egg and 3 polar bodies.

37. The Meiosis Square Dance

38. Homologous chromosomes

39. Prophase I

40. Synapsis and crossing over

41. Metaphase I -- Notice the synpasis

42. Anaphase I

43. Prophase 2 – similar to mitosis
Replication does not occur between meiosis 1 and meiosis 2

44. Metaphase 2

45. Anaphase 2 –

46. Telophase 2 – chromosome number is now ½ of the original

47. Cytokinesis – meiosis results in 4 daughter cells

48. Answers to Homework

49. Summary
The diploid number (2n) of chromosomes is reduced by 1/2 to the haploid number (n)
Eggs and sperm are formed
Crossing Over occurs—lots of variation
Variations rarely occur in MITOSIS
Variations often occur in MEIOSIS

50. Results of Meiosis
Mitosis is associated with growth and asexual reproduction
Meiosis is associated with sexual reproduction
Spermatogenesis: the production of sperm
Produces 4 sperm
Oogenesis: the production of ova or eggs
Produces one egg and three polar bodies