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?
1
0
2
0.25
3
0.5
4
1
Official Solution
Correct Option: (1)
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:
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).
Determine the Genotypes of Parents:
The genotype of the first parent is YY.
The genotype of the second parent is yy.
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).
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.
Conclusion: The proportion of homozygous recessive (yy) offspring in the F1 generation is 0.