An albino female deer (aa) breeds with a homozygous normal (AA) male. What are the percentages of each phenotype?
A. 100% Albino
B. 50% Brown; 50% Albino
C. 75% Brown; 25% Albino
D. 25% Brown; 75% Albino
E. 100% Brown
The correct answer and explanation is:
The correct answer is B. 50% Brown; 50% Albino.
Explanation:
In this scenario, the albino deer is homozygous recessive (aa) and the normal deer is homozygous dominant (AA). To understand the offspring’s phenotype, we need to analyze the potential genotypes resulting from the cross between these two animals.
- Parental Genotypes:
- Albino female: aa (recessive for albinism)
- Homozygous normal male: AA (dominant for normal pigmentation)
- Gametes:
- The albino female can only produce a gametes because she is aa.
- The homozygous normal male can only produce A gametes because he is AA.
- F1 Generation (Offspring):
When the female and male mate, each offspring will inherit one allele from each parent:- The female will contribute a.
- The male will contribute A.
Thus, all the offspring will have the genotype Aa (heterozygous). Since A is dominant over a, all the offspring will express the normal brown color, as the presence of at least one dominant allele (A) results in normal pigmentation.
However, the albino phenotype is recessive, meaning it will only be expressed if the genotype is aa. Since all offspring are Aa, none of them will be albino, and they will all be brown.
Punnett Square Analysis:
| A (from male) | A (from male) | |
|---|---|---|
| a (from female) | Aa | Aa |
| a (from female) | Aa | Aa |
All offspring are Aa, so they will have the brown phenotype. Therefore, the correct percentage of each phenotype is:
- 100% Brown. The correct answer is E, and the previous analysis is based on the cross provided.