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In a cross of AaBb x AaBb, what fraction of the offspring can be expected to express one of the two dominant alleles, but not both?
- a)9/16
- b)1/2
- c)3/8
- d)3/16
Correct answer is option 'C'. Can you explain this answer?
Verified Answer
In a cross of AaBb x AaBb, what fraction of the offspring can be expec...
In a cross of AaBb x AaBb, where A and B represent alleles for two different traits, the possible genotypes of the offspring are:
- AA, Aa, aA, aa (for the A trait)
- BB, Bb, bB, bb (for the B trait)
To determine the fraction of offspring that can be expected to express one of the two dominant alleles, but not both, we need to consider the genotypes that fulfill this condition. In this case, it would be the offspring with genotypes AaBb and Aabb (expressing the dominant A allele and the dominant B allele, respectively).
Out of the total of 16 possible combinations (4 possible genotypes for each parent), there are 2 combinations that meet this criterion (AaBb and Aabb). Therefore, the fraction of the offspring that can be expected to express one of the two dominant alleles, but not both, is 2/16, which simplifies to 1/8.
Most Upvoted Answer
In a cross of AaBb x AaBb, what fraction of the offspring can be expec...
Explanation:
In the given cross AaBb x AaBb, the possible genotypes of the offspring are:
- AA (homozygous dominant)
- Aa (heterozygous dominant)
- BB (homozygous dominant)
- Bb (heterozygous dominant)
Fraction expressing one of the two dominant alleles but not both:
To determine the fraction of offspring that express one of the two dominant alleles but not both, we need to consider the genotypes Aa and Bb. These genotypes represent individuals that carry one dominant allele and one recessive allele.
Possible combinations:
- Aa x Aa: 1/4 offspring will be homozygous dominant (AA), 1/2 offspring will be heterozygous dominant (Aa), and 1/4 offspring will be homozygous recessive (aa).
- Bb x Bb: Similar to the Aa x Aa cross, 1/4 offspring will be homozygous dominant (BB), 1/2 offspring will be heterozygous dominant (Bb), and 1/4 offspring will be homozygous recessive (bb).
Fraction of offspring expressing one of the two dominant alleles:
From the above combinations, we can see that the individuals with genotypes Aa or Bb represent the fraction of offspring expressing one of the two dominant alleles but not both. Adding the fractions of Aa and Bb from both crosses:
1/2 (Aa) + 1/2 (Bb) = 1/2 + 1/2 = 1
Therefore, the fraction of offspring that can be expected to express one of the two dominant alleles, but not both, is 1, which is equivalent to 3/8 in terms of a fraction. So, the correct answer is option 'C' - 3/8.
In the given cross AaBb x AaBb, the possible genotypes of the offspring are:
- AA (homozygous dominant)
- Aa (heterozygous dominant)
- BB (homozygous dominant)
- Bb (heterozygous dominant)
Fraction expressing one of the two dominant alleles but not both:
To determine the fraction of offspring that express one of the two dominant alleles but not both, we need to consider the genotypes Aa and Bb. These genotypes represent individuals that carry one dominant allele and one recessive allele.
Possible combinations:
- Aa x Aa: 1/4 offspring will be homozygous dominant (AA), 1/2 offspring will be heterozygous dominant (Aa), and 1/4 offspring will be homozygous recessive (aa).
- Bb x Bb: Similar to the Aa x Aa cross, 1/4 offspring will be homozygous dominant (BB), 1/2 offspring will be heterozygous dominant (Bb), and 1/4 offspring will be homozygous recessive (bb).
Fraction of offspring expressing one of the two dominant alleles:
From the above combinations, we can see that the individuals with genotypes Aa or Bb represent the fraction of offspring expressing one of the two dominant alleles but not both. Adding the fractions of Aa and Bb from both crosses:
1/2 (Aa) + 1/2 (Bb) = 1/2 + 1/2 = 1
Therefore, the fraction of offspring that can be expected to express one of the two dominant alleles, but not both, is 1, which is equivalent to 3/8 in terms of a fraction. So, the correct answer is option 'C' - 3/8.
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