Sex-linked Inheritance

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

Sex Inheritance Gametes X X X XX XX X X

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.

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)

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

**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

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

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.

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

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.

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.

X F X f X F X F X F X F X f X F X f

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?

X C

X C X C

X C X C X c

X C X C X C X c

X C X C X C X C X C X c

X C X c X C X C X C X C X c

X C X c X C X C X C X C X c X C X c

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?

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

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

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

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

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

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

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

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

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?

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?

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

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?

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

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?

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

Muscular Dystrophy: Xm (XM = normal)

Muscular Dystrophy: Xm (XM = normal) X M

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

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

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

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

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