Question

a cross was performed, and the offspring shown to the right were produced. what is the most likely genotype for the parents?
options:

• bbee × bbee
• bbee × bbee
• bbee × bbee
• bbee × bbee

offspring counts:

• 10 mice with black fur, black eyes
• 2 mice with black fur, red eyes
• 3 mice with white fur, black eyes
• 1 mouse with white fur, red eyes

Explanation:

Step1: Analyze Offspring Phenotypes

Offspring phenotypes: 10 black fur/black eyes, 2 black fur/red eyes, 3 white fur/black eyes, 1 white fur/red eyes. Let's assume fur color (B - black, b - white) and eye color (E - black, e - red) are two traits.

Step2: Evaluate Each Cross

• Option A: BbEe × bbEE

For fur: Bb × bb → 50% Bb (black), 50% bb (white).
For eyes: Ee × EE → 100% E_ (black).
Offspring eyes should all be black, but we have red - eyed offspring. Eliminate A.

• Option B: BbEE × Bbee

For fur: Bb × Bb → 75% B_ (black), 25% bb (white).
For eyes: EE × ee → 100% Ee (black).
Offspring eyes should all be black, but we have red - eyed offspring. Eliminate B.

• Option C: BbEe × BbEe

For fur: Bb × Bb → 75% B_ (black), 25% bb (white).
For eyes: Ee × Ee → 75% E_ (black), 25% ee (red).
Calculate expected ratios:
Black fur/black eyes: \( 0.75\times0.75 = 0.5625 \)
Black fur/red eyes: \( 0.75\times0.25 = 0.1875 \)
White fur/black eyes: \( 0.25\times0.75 = 0.1875 \)
White fur/red eyes: \( 0.25\times0.25 = 0.0625 \)
Total offspring: \( 10 + 2+3 + 1=16 \).
Expected counts:
Black/black: \( 16\times0.5625 = 9 \) (close to 10).
Black/red: \( 16\times0.1875 = 3 \) (close to 2).
White/black: \( 16\times0.1875 = 3 \) (close to 3).
White/red: \( 16\times0.0625 = 1 \) (matches 1).

• Option D: BBEE × bbee

For fur: BB × bb → 100% Bb (black).
For eyes: EE × ee → 100% Ee (black).
Offspring should all be black fur/black eyes, but we have white - fur and red - eyed offspring. Eliminate D.

Answer:

C. BbEe × BbEe