Name:_____________________________________

# Practice Problems: Sex 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 R X r _________ X R Y _________ X r X r _______

X R X R _________ X r Y _________

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 Xr Xr and a red-eyed male XR Y .

How many are:

white eyed, male ____
white eyed, female ____
red eyed, male ____
red eyed, female ____

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

What are the genotypes of the parents: _________ and ____________

How many 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 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? ________

## Human Sex Linkage

6. 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)

 X H X H = female, normal X H X h = female, carrier X h X h = female, hemophiliac X H Y = male, normal X h Y= male, hemophiliac

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

How many children will have the disease?  _____

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

How many children will have the disease?  _____

What is the sex of the child with the disease? _____

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

How many children will have the disease?  _____

What is the sex of the child with the disease? _____

### Calico Cat Genetics

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

Female, Calico = X B X R          Male, Black = X B Y

How many offspring will be:

Female and calico ____  Female and black ____
Male and black ___          Male and orange ___
Male and calico ____

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

What percentage of the kittens will be calico and female? _____
What color will all the male cats be? _____