Question

In mice, a trait is determined by a dominant allele Y and recessive allele y. What proportion of the offspring from a YY × yy cross is expected to be homozygous recessive in F1 generation?

• A. 0
• B. 0.25
• C. 0.5
• D. 1

Answer 1

The Correct Option is A

To determine the proportion of the offspring from a YY × yy cross that is expected to be homozygous recessive in the F1 generation, we need to understand the basic principles of Mendelian genetics. Here’s a step-by-step explanation:

1. Identify the Alleles:
   • The dominant allele is Y, which determines the dominant trait when present.
   • The recessive allele is y, which determines the recessive trait only when the allele is in homozygous condition (yy).
2. Determine the Genotypes of Parents:
   • The genotype of the first parent is YY. 
   • The genotype of the second parent is yy.
3. Set Up the Punnett Square:
   A Punnett square helps visualize the possible genotypes of the offspring.
    

	Y	Y
y	Yy	Yy
y	Yy	Yy

All offspring will be Yy (heterozygous).

1. Analyze the Results:
   • From the Punnett square, all F1 offspring have the genotype Yy.
   • Since none of the offspring have the genotype yy, there are zero homozygous recessive individuals.
2. Conclusion:
   The proportion of homozygous recessive (yy) offspring in the F1 generation is 0.

Therefore, the correct answer is 0.