Genetics Worksheet (Page 5 of 8) in pdf

Section D: Beyond Mendel – Patterns of Inheritance

Codominance –

1. Crow’s (the black bird) feet can have orange markings or have brown markings. When a crow with

orange (O) markings is mated with a crow with brown (B) markings, the resulting phenotype is both

orange and brown spots on the feet. Cross an orange footed crow with a crow that has orange and

brown spots on its feet. What are the genotypic and phenotypic ratios of the offspring?

2. Why is the crow’s markings considered codominant inheritance?

3. You are exploring the jungle and find a new species of plant. Some of the flowers are red and some

are yellow. If the inheritance pattern is codominant, what would you expect the heterozygous

phenotype to be?

Incomplete Dominance –

4. Rats can have a variety of fur color. When a black (B) furred rat is crossed with a white (W) furred rat,

the resulting phenotype is gray fur. Cross a gray furred rat with a black furred rat. What are the

phenotypic ratios of the offspring?

5. Why are the rat’s fur color considered incomplete dominance?

6. If the red and yellow alleles in the mystery jungle plant above showed incomplete dominance, what

would you expect the heterozygous phenotype to be?

Sex-Linked –

7. In fruit flies, eye color is sex-linked. Red is dominant to white. Cross a white eyed female X

with a

red-eyed male X

Y. What are the genotypes and phenotypes of the offspring?

8. In humans, hemophilia is a recessive 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) 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?

= female, normal

= female, carrier

= female, hemophilia

male, normal

male, hemophilia

9. A woman who is a carrier marries a normal man. If they have a daughter,

what are the possible phenotypes? If they have a son, what are the possible phenotypes?

Genetics Worksheet Page 5