Pedigrees Practice Key

In humans, albinism is a recessive trait. The disorder causes a lack of pigment in the skin and hair, making an albino appear very pale with white hair and pale blue eyes. This disorder also occurs in animals, a common albino found in a laboratory is the white rat. The pedigrees below trace the inheritence of the allele that causes albinism.

1. Given the following genotypes, describe the phenotypes (normal or albino)

AA = _______normal______
Aa = ______normal_______
aa = _____albino_________

2. Fill out the blanks on the pedigree below. Remember that gray squares indicate that the person has the two recessive alleles (aa) and is an albino

aa x Aa
Aa, Aa, aa


3. How many children does this family have? __3____
What are the sexes of the children? ___female____

7. Fill out the blanks of the pedigree below (AA, Aa, aa)

Aa x Aa
aa, Aa - Aa
aa - Aa, aa, Aa or AA *

* When two hetorzygotes are crossed (Aa x Aa) offspring may be unknown and can be either AA or Aa.

pedigree 3

8. How many children does the original couple have? _2__
9. How many grandchildren? ____3__


4. Fill out the blanks of the pedigree below (AA, Aa, or aa)

Aa x aa
aa , Aa, Aa - Aa

pedigree 2

5. How many children does the original couple have? _3_

6. How many grandchildren does the original couple have? _1__
What is the sex of the grandchild? __male__

*Note: The rat pedigree is not a traditional pedigree, it is illustrated here simply to provide a challenge to students.

10. Rats can produce a lot more offspring than humans, making a pedigree more difficult to manage. A researcher has four female white rats named April, May, June, and July. One night, the cage was left open in the lab and a brown rat got into the female's cage. Six weeks later, the rats had litters of babies of varying colors. Two of the offspring managed to reproduce before the researcher was able to sort out the mess. Determine genotypes of the rats in this pedigree. rat pedigree

Note that the offspring of the first cross between Manny and each female will produce either albino offspring (represented by the gray squares) or brown offspring that are heterozygous (Aa).

In the second generation offspring, it is unknown whether the brown offspring inherited an albino allele.