Question

punnett square
name:_____________ date:_____
a. in laboratory mice, gray coat color (g) is dominant over albino coat color (g). cross a female gg with a male gg and answer the questions that follow:
gg × gg

1. how many possible genotypes are there among the offspring?
2. how many possible phenotypes are there among the offspring?
3. what percentage of the offspring are gray?
4. what percentage of the offspring are albino?
5. what color is the female parent?
6. what color is the male parent?
7. what is the phenotypic ratio of gray coat color to albino coat color?

b. in rabbits, the allele for black coat (b) is dominant over the allele for a brown coat (b). cross a female rabbit that is homozygous dominant for black coat with a heterozygous male rabbit. then, answer the questions that follow:
bb × bb

1. how many possible genotypes are there among the offspring?
2. how many possible phenotypes are there among the offspring?
3. what percentage of the offspring are black - coated?
4. what percentage of the offspring are brown - coated?
5. what color is the male parent?

Explanation:

Part A (Gg × gg)

Step1: Confirm Punnett Square

Female alleles: $G, g$; Male alleles: $g, g$

$$\begin{array}{c|cc} & G & g \\ \hline g & Gg & gg \\ g & Gg & gg \\ \end{array}$$

Step2: Count genotypes

Offspring genotypes: $Gg, gg$ → 2 total.

Step3: Count phenotypes

Gray ($Gg$) and albino ($gg$) → 2 total.

Step4: Calculate gray percentage

$\frac{2}{4} \times 100\% = 50\%$

Step5: Calculate albino percentage

$\frac{2}{4} \times 100\% = 50\%$

Step6: Identify female parent color

Female is $Gg$ (dominant $G$) → gray.

Step7: Identify male parent color

Male is $gg$ (recessive only) → albino.

Step8: Find phenotypic ratio

Gray:Albino = 2:2 = 1:1

Part B (BB × Bb)

Step1: Build Punnett Square

Female alleles: $B, B$; Male alleles: $B, b$

$$\begin{array}{c|cc} & B & B \\ \hline B & BB & BB \\ b & Bb & Bb \\ \end{array}$$

Step2: Count genotypes

Offspring genotypes: $BB, Bb$ → 2 total.

Step3: Count phenotypes

All have dominant $B$ → only black coat, 1 total.

Step4: Calculate black percentage

$\frac{4}{4} \times 100\% = 100\%$

Step5: Calculate brown percentage

0 brown offspring → 0%

Step6: Identify male parent color

Male is $Bb$ (dominant $B$) → black.

Answer:

Part A:

1. 2
2. 2
3. 50%
4. 50%
5. Gray
6. Albino
7. 1:1

Part B:

Punnett Square:

$$\begin{array}{c|cc} & B & B \\ \hline B & BB & BB \\ b & Bb & Bb \\ \end{array}$$

1. 2
2. 1
3. 100%
4. 0%
5. Black