Sex-linked Inheritance

Transcription

1 Sex-linked Inheritance

2 Some Review: Autosomes: Non-sex chromosomes (#1-22 homologous pairs) Sex Chromosomes: Chromosome pair #23 Female XX Male X

3 Sex Inheritance Gametes X X X XX XX X X

4 Sex-linkage Trait is carried on the X chromosome. The chromosome is too small to carry other traits besides the one determining the male sex characteristics.

5 Ex. In Drosophila (fruit flies): P: White-eyed male x Red-eyed female F1: All Red eyed F2: ¾ red eyes, ¼ white (all male)

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7 **you know you are dealing with a sexlinked trait when mostly MALES exhibit the trait!!!**

8 **you know you are dealing with a sexlinked trait when mostly MALES exhibit the trait!!!** Carrier: Only females have two X chromosomes a carrier is heterozygous and carries a recessive trait but shows the dominant trait Therefore the recessive trait is masked and not exhibited but the gene is still there to be passed on. X R X r

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10 We can also use Punnett squares in questions concerning sex-linked traits

11 We can also use Punnett squares in questions concerning sex-linked traits Instead of using a lone letter to represent each allele, we connect it to the sex chromosome.

12 We can also use Punnett squares in questions concerning sex-linked traits Instead of using a lone letter to represent each allele, we connect it to the sex chromosome. Ex. X A X a or X A

13 We can also use Punnett squares in questions concerning sex-linked traits Instead of using a lone letter to represent each allele, we connect it to the sex chromosome. Ex. X A X a or X A X A or X A or X a The dominant allele is written as a capital letter and the recessive allele as a lowercase letter this is a form of complete dominance.

14 We can also use Punnett squares in questions concerning sex-linked traits Instead of using a lone letter to represent each allele, we connect it to the sex chromosome. Ex. X A X a or X A The dominant allele is written as a capital letter and the recessive allele as a lowercase letter just like in complete dominance. The has no allele attached.

15 X F X f X F X F X F X F X f X F X f

16 Human examples (notice that all are recessive traits): Color Blindness: X c (X C = normal color vision) Ex. Two normal-visioned parents produce a color blind son. What are the genotypes of the parents? What are the chances of their next child being a color-blind daughter?

17 X C

18 X C X C

19 X C X C X c

20 X C X C X C X c

21 X C X C X C X C X C X c

22 X C X c X C X C X C X C X c

23 X C X c X C X C X C X C X c X C X c

24 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy?

25 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c

26 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C

27 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X c

28 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c

29 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c

30 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c X C

31 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c X C X c

32 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c X C X c

33 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c X C X c

34 Ex. If a color blind man marries a woman whose father was color blind; what is the probability of their first child being a color blind boy? X c X C X C X c X c X c X c X C X c Color Blind Boy = 1/4

35 Hemophilia: X h (X H = normal blood clotting) Ex. a man, whose father was a hemophiliac but who s clotting time was normal, marries a woman with no record of hemophilia in her ancestry. What are the chances of hemophilia in their children?

36 Hemophilia: X h (X H = normal blood clotting) Ex. a man, whose father was a hemophiliac but who s clotting time was normal, marries a woman with no record of hemophilia in her ancestry. What are the chances of hemophilia in their children? X H X H 0% chance X H

37 Ex. A woman whose father was a hemophiliac, but who is not herself a bleeder, marries a normal man. What is the chance of hemophilia in their children?

38 Ex. A woman whose father was a hemophiliac, but who is not herself a bleeder, marries a normal man. What is the chance of hemophilia in their children? Hemophilia Children = 1/4

39 Ex. If a boy s father has hemophilia and his mother s cells have one gene for the disease, what is the chance the boy will inherit the disease?

40 Ex. If a boy s father has hemophilia and his mother s cells have one gene for the disease, what is the chance the boy will inherit the disease? X H X H ½ or 50% chance X H

41 Ex. If a woman who is not a carrier of genes for hemophilia is married to a man who is a hemophiliac, what percentage of their male offspring could be expected to be hemophiliac?

42 Ex. If a woman who is not a carrier of genes for hemophilia is married to a man who is a hemophiliac, what percentage of their male offspring could be expected to be hemophiliac? 0% chance

43 Muscular Dystrophy: Xm (XM = normal)

44 Muscular Dystrophy: Xm (XM = normal) X M

45 Muscular Dystrophy: Xm (XM = normal) X M X m X M

46 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M

47 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M X M X m

48 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M X M X m X M

49 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M X M X m X M X m

50 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M X M X m X M X m

51 Muscular Dystrophy: Xm (XM = normal) X M X m X M X M X M X M X m X M X m