Question

pedigrees practice
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 inheritance of the alleles that causes albinism.

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

aa =
aa =

aa =

1. fill out the blanks on the pedigree below.

1. how many children does this family have?

what are the sexes of the children?

1. fill out the blanks of the pedigree below (aa, aa, or aa)

1. how many children does the original couple have?

1. how many grandchildren does the original couple have?

what is the sex of the grandchild?

1. fill out the blanks of the pedigree below (aa, aa, aa)

1. how many children does the original couple have?
2. how many grandchildren?

1. 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.

Explanation:

Step1: Define recessive trait rules

Albinism is recessive: $aa$ = albino; dominant allele $A$ masks trait, so $AA/Aa$ = normal.

Step2: Solve Q1 phenotypes

AA = normal (dominant homozygous)
Aa = normal (carrier, dominant heterozygous)
aa = albino (recessive homozygous)

Step3: Fill Q2 pedigree (recessive trait)

Affected male = $aa$. Offspring has $aa$ female, so both parents must pass $a$. Unaffected female = $Aa$. Unaffected daughters = $Aa$ (inherit $A$ from mother, $a$ from father).

• Father (shaded square): $aa$
• Mother (circle): $Aa$
• Daughter 1 (circle): $Aa$
• Daughter 2 (circle): $Aa$
• Daughter 3 (shaded circle): $aa$

Step4: Answer Q3

Count offspring: 3 children, all female (circles).

Step5: Fill Q4 pedigree (recessive trait)

Affected female = $aa$. Unaffected male must pass $A$ to unaffected sons, so male = $Aa$. Affected daughter = $aa$. Unaffected sons = $Aa$. Son's partner is normal; their affected son = $aa$, so partner = $Aa$.

• Father (square): $Aa$
• Mother (shaded circle): $aa$
• Daughter (shaded circle): $aa$
• Son 1 (square): $Aa$
• Son 2 (square): $Aa$
• Son 2's partner (circle): $Aa$
• Grandson (shaded square): $aa$

Step6: Answer Q5-Q6

Q5: Original couple has 3 children.
Q6: 1 grandson (shaded square, male).

Step7: Fill Q7 pedigree (recessive trait)

Affected female child = $aa$, so both parents pass $a$: parents = $Aa$. Original couple has affected child, so both = $Aa$. Unaffected son (child of original couple) = $Aa$ (since parents are $Aa$). His partner is normal; their affected son = $aa$, so partner = $Aa$. Their affected daughter = $aa$.

• Original father (square): $Aa$
• Original mother (circle): $Aa$
• Affected daughter (shaded circle): $aa$
• Son (square): $Aa$
• Son's partner (circle): $Aa$
• Son's affected son (shaded square): $aa$
• Son's unaffected partner (circle): $Aa$
• Son's affected daughter (shaded circle): $aa$

Step8: Answer Q8-Q9

Q8: Original couple has 2 children.
Q9: Original couple has 4 grandchildren.

Step9: Rat pedigree genotypes (white = albino $aa$, brown = normal $A\_$)

White females (April/May/June/July) = $aa$. Brown male (Manny) must be $AA$ (all offspring with white females are brown, so no $a$ passed). Brown offspring = $Aa$ (inherit $A$ from father, $a$ from mother). When $Aa$ brown rats mate:

• Affected (white) offspring = $aa$
• Normal (brown) offspring = $AA$ or $Aa$

Answer:

1.
AA = normal
Aa = normal (carrier)
aa = albino
2.
Father (shaded square): $aa$
Mother (circle): $Aa$
Daughter 1 (circle): $Aa$
Daughter 2 (circle): $Aa$
Daughter 3 (shaded circle): $aa$
3.
Number of children: 3; Sexes: all female
4.
Father (square): $Aa$
Mother (shaded circle): $aa$
Daughter (shaded circle): $aa$
Son 1 (square): $Aa$
Son 2 (square): $Aa$
Son 2's partner (circle): $Aa$
Grandson (shaded square): $aa$

1. 3
2. Number of grandchildren: 1; Sex: male

7.
Original father (square): $Aa$
Original mother (circle): $Aa$
Affected daughter (shaded circle): $aa$
Son (square): $Aa$
Son's partner (circle): $Aa$
Son's affected son (shaded square): $aa$
Son's unaffected partner (circle): $Aa$
Son's affected daughter (shaded circle): $aa$

1. 2
2. 4

10.

• Manny (brown male): $AA$
• April/May/June/July (white females): $aa$
• All brown offspring of Manny and white females: $Aa$
• White (albino) offspring of brown ($Aa$) parents: $aa$
• Brown offspring of brown ($Aa$) parents: $AA$ or $Aa$