Genetics X Linked Genes

Genetics: X Linked Genes

****In fruit flies, eye color is a sex linked trait. Red is dominant to white ****

1. What are the sexes and eye colors of flies with the following genotypes:

X^RX^r_____________ X^RY ____________ X^rX^r ___________

X^RX^R____________ X^rY____________

2. What are the genotypes of these flies:

white eyed, male ____________ red eyed female (heterozygous) ________

white eyed, female ___________ red eyed, male ___________

3. Show the cross of a white eyed female X^rX^r with a red-eyed male X^RY .

4. Show a cross between a pure red eyed female and a white eyed male.

What are the genotypes of the parents: ___________& _______________

How many offspring are:

§ white eyed, male ____

§ white eyed, female ____

§ red eyed, male ____

§ red eyed, female ____

5. Show the cross of a red eyed female (heterozygous) and a red eyed male. What are the genotypes of the parents? __________ & ___________

How many offspring are:

§ white eyed, male____

§ white eyed, female ___

§ red eyed, male ____

§ red eyed, female ____

Math: What if in the above cross, 100 males were produced and 200 females.

How many total red-eyed flies would there be?

In humans, hemophilia is a sex linked trait. Females can be normal, carriers, or have the disease. Males will either have the disease or not (but they won’t ever be carriers).

XX = female, normal

XX^h = female, carrier

X^hX^h = female, hemophiliac

XY = male, normal

X^hY = male, hemophiliac

6. Show the cross of a man who has hemophilia with a woman who is a carrier.

• What is the probability that their children will have the disease? __________

7. A woman who is a carrier marries a normal man. Show the cross.

§ What is the probability that their children will have hemophilia? __________________

§ What sex will a child in the family with hemophilia be? __________________

8. A woman who has hemophilia marries a normal man. How many of their children will have hemophilia, and what is their sex?

In cats, the gene for calico (multicolored) cats is codominant. Females that receive a B and an R gene have black and orange splotches on white coats. Males can only be black or orange, but never calico.

Here’s what a calico female’s genotype would look like: X^BX^R

9. Show the cross of a female calico cat with a black male.

What percentage of the kittens will be black and male? ______

What percentage of the kittens will be calico and male? ______

What percentage of the kittens will be calico and female? _____

10. Show the cross of a female black cat, with a male orange cat.

What percentage of the kittens will be calico and female? _____

What color will all the male cats be? ______