1. MEIOSIS
Making Sex Cells

2. Somatic cell = body cell
Get the Lingo Down!!!
Somatic cell = body cell
Skin Nerve Blood

3. Human Chromosomes How many chromosomes? 46
How many pairs of chromosomes? 23

4. Homologous Chromosomes
Two sister chromatids joined at the centromere From MOTHER plus
Two sister chromatids joined at the centromere From FATHER =
All Four Chromatids carrying genes controlling the same inherited characteristics

6. Loci The place on a chromosome where a specific gene is located
The plural is "loci," not "locuses."
EXAMPLE: gene for hair color
Gene for height

7. Autosomes Any chromosome that is not a sex chromosome
Humans - #1 through #22

8. Sex Chromosomes Female = XX Male = XY Chromosome #23
Is this a male or female?

9. Is this a male or female?

10. Where do we get the pair of chromosomes?
One set from our father
One set from our mother

11. Human Cells
Diploid number 2n 46
somatic cells
Haploid number n 23
sex cells

12. Sex Cells
“Gametes”
EX: Egg and Sperm

13. Single set of chromosomes
Are Gametes n or 2n? N
Single set of chromosomes

14. Are Gametes haploid or diploid?-n
23 chromosomes
egg 23
sperm

15. Fertilization Fusing of Egg and Sperm Woo-Hoo! What’s the
Fertilized egg called?
Zygote

16. Where are the sex cells made?
Testes make sperm
Ovaries make eggs
Only in reproductive organs

17. What is the process…
In which sex cells are made?
MEIOSIS

18. How many cells formed? Haploid or Diploid?
4 haploid diploid

19. MEIOSIS INTERPHASE Yes, the chromosomes duplicate
Still chromatin, loose

20. Meiosis I: Prophase I
90% of meiosis time

21. Meiosis I: Prophase I
Synapsis: formation of a tetrad (4 homologous chromosomes)

22. Let’s Review: All DNA and Protein

23. With Jonathan Edwards…whatever happened to him, anyway?

24. Let’s See a Close-up: Crossing Over

25. Chiasma Sites of crossing over Appear as X-shaped regions
Site where two homologous chromosomes are attached to each other

26. Genetic Recombination
The production of gene combinations different from those carried by the original chromosomes
ADVANTAGE: increases diversity

27. What else happens Prophase I?
What dissolves?
Nuclear Membrane and Nucleolus

28. What else happens Prophase I?
What also forms?
spindles

29. Meiosis I: Metaphase I
Where are the tetrads lined up? Metaphase plate

30. Meiosis I: Anaphase I Where are the sister chromatids going?
Apart to the poles
NOTE: the double strands

31. Meiosis I: Telophase I Note the double strands at the poles
Cytokinesis begins

32. Interkinesis/Cytokinesis
Some cells will go into a temporary chromatin-forming interphase (like in humans) called interkinesis

33. Interkinesis/Cytokinesis
Some will immediately go into Prophase II
NOT ALL CELLS DO THIS AT THE SAME TIME…BUT ALL WILL EVENTUALLY GO INTO PROPHASE II

34. Interkinesis/Cytokinesis
(Different than mitosis interphase, however)
NO NEW DUPLICATION OF CHROMOSOMES…
FURTHER DIVISION OF THE CHROMOSOMES WILL OCCUR

35. Meiosis II: Prophase II
How many cells are there? 2
What is dissolving?
Nuclear membrane
What’s forming? New spindles

36. Meiosis II: Metaphase II
How many cells? 2
Where are the chromatids lined up? Metaphase (equatorial plate)

37. Meiosis II: Anaphase II
How many cells? 2
What are the single chromosomes doing? Moving to poles

38. Meiosis II:Telophase II
How many cells will result at the end? 4
Will the cells be haploid or diploid? Haploid

39. Name the Phase (Meiosis I)

40. Name the Phase (Meiosis II)

41. Sperm Meiosis All cells same size

42. Sperm maturing in a seminiferous tubule

43. Egg Meiosis One large egg, 3 small polar bodies
“oogenesis”

44. Follicle and egg

45. Results in 2 daughter cells
Contrast
MITOSIS
1 division
(PMAT)
Results in 2 daughter cells
MEIOSIS
2 divisions
(PMAT) I and (PMAT) II
Results in 4 daughter cells

46. Contrast MITOSIS Diploid offspring Makes somatic cells MEIOSIS
Haploid offspring
Makes sex cells

47. Contrast
MITOSIS
Makes identical cells
Same number of chromosomes
MEIOSIS
Makes similar cells
Half the number of chromosomes

48. Independent Assortment
This means that traits are transmitted to offspring independently of one another.
Independent Assortment Animation

49. Independent Assortment
In other words,
RANDOM COMBINATION OF ALLELES APPEAR IN THE GAMETES

50. How many possible combinations are there?
n = haploid number
22 = ? 8

51. When one man (223) combines with one woman (223)?
How many combos?
When one man (223) combines with one woman (223)?
246

52. How many combos from independent assortment:
HUMANS
223 = ?
About 8 million
(8,388,608)

53. If only one crossover occurs, how many possible combinations?
(70,368,744,000,000)

54. With fertilization and crossing-over, how many combos possible?
(4 23) 2 = 4,951,760,200,000,000,000,000,000,000

55. Wait a second…
What are alleles?

56. Alleles Different Versions of Genes
FOR EXAMPLE: B = brown eye color b = blue eye color
FOR EXAMPLE: T = Tall
t = short

57. More Allele Examples (fruit)
Hi = Hard rind inhibitor
Hr = Hard rind
l = light fruit color
Rd = dominant = Red skin color of fruit
St = stripped fruit lengthwise
Rd = dominant = Red skin color of fruit

58. Dog Breeds: Lots of Alleles

59. Dog Color Alleles in order of decreasing dominance:
Ay - agouti "red" (black, if any, appears in restricted areas only) Aw - "white-bellied" agouti
A - solid agouti at - black & tan a – non agouti (recessive black)
Ea - dominant black
Em - black mask

60. Why are the cells formed in meiosis different from the parents?
Random Fertilization (who ya have sex with)
Independent Assortment
Crossing Over

61. So an advantage of Meiosis…
A tremendous amount of genetic variation is possible!

62. Let’s Review Three sources of genetic variability:
1. Crossing over during prophase I of meiosis
2. Independent orientation of chromosomes at metaphase I
3. Random fertilization

63. Karyotype
An orderly display of magnified images of the individual’s chromosomes
Shows the chromosomes as they appear in metaphase

64. What is a Normal Karyotype?
We are supposed to have 46 total chromosomes in each cell (22 pairs of autosomes = 44, + 2 sex chromosomes).

65. Preparing a Karyotype 1. Use lymphocytes (white blood cells)
2. Chemical to stimulate division
3. Chemical to stop in metaphase
(stop spindle fibers forming)

66. Preparing a Karyotype (cont)
4. Centrifuged to remove white blood cells
5. Chromosomes spread out in hypotonic solution.
6. Drop on a slide.
7.Sort by size and shape.

67. Resulting Photograph
Sort by size and shape
Largest to smallest

68. Amniocentesis
Take fluid from amniotic fluid around the baby

69. Spectral Karyotype

70. Normal Karyotype
WHY?

71. Down Syndrome Karyotype
Trisomy 21

72. Down Syndrome
Trisomy 21
Folds over eyes
Sluggish muscles
Mental Problems

73. Down Syndrome The most common chromosome number abnormality Round face
flattened nose bridge
small, irregular teeth

74. Down Syndrome Short Stature heart defects
susceptibility to respiratory infection , leukemia and Alzheimer’s

75. Does the mother’s age matter?
As the age of the mother increases above 30, the frequency of Trisomy 21 also increases

76. Abnormal Sex Chromosomes
47 XXY syndrome
male
testes small (sterile)
breast enlargement
feminine body contours
also XXYY, XXXY, XXXXY
Klinefelter’s

77. TURNER SYNDROME XO (only one X) short
often web of skin between neck and shoulders
sterile
poor breast development

78. Turner Karyotype

79. Why are the cells formed in meiosis different from the parents?
Random Fertilization (who ya have sex with)
Independent Assortment
Crossing Over

80. How many possible combinations are there?
n = haploid number
22 = ? 8

82. DELETION
Fragment of the chromosome is lost

83. Duplication
Fragment of one chromosome attaches to a homologous chromosome

84. Translocation
Fragment reattaches in reverse direction (less likely to produce harm)

85. INVERSION
The chromosome breaks in two places, a piece of the chromosome is removed and the chromosome pieces remaining rejoin.
Less likely to remove harm

86. The left one is normal and the right one is inverted near the centromere. Inversions, by definition, do not involve loss or gain of chromosomal material.
INVERSION 46,XY,inv(16)

87. 45,XX,rob(13,14) A Robertsonian translocation
(an end to end fusion of #13 and #14 There is no net gain or loss of genetic material in this person so they would have a normal phenotype.
45,XX,rob(13,14) A Robertsonian translocation

88. Locus

90. Broccoli + Cauliflower = Broccoflower

91. Male Lion X Female Tiger
Liger