biology : class12 Genotypic Classes : Dihybrid Cross, Independent Assortment : Law of Independent Assortment MCQ Questions and Answers
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Genotypic Classes
MCQ questions and answers.
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MCQ Questions
1. How many different genotypic classes are produced in the F2 generation of a dihybrid cross AaBb × AaBb?
A.
4
B.
6
C.
9
D.
16
Correct Answer:
9
Explanation:
Each gene pair produces three genotypes: AA, Aa, aa and BB, Bb, bb. Therefore, the total number of genotypic classes is 3 × 3 = 9.
2. What is the genotypic ratio obtained from the dihybrid cross AaBb × AaBb?
A.
9:3:3:1
B.
1:2:1
C.
1:2:1:2:4:2:1:2:1
D.
3:1
Correct Answer:
1:2:1:2:4:2:1:2:1
Explanation:
The genotypic ratio for AaBb × AaBb is formed by combining the monohybrid ratios 1:2:1 for both genes, giving 1:2:1:2:4:2:1:2:1.
3. Which genotype represents one of the nine genotypic classes in the F2 generation of AaBb × AaBb?
A.
AAbb
B.
AAB
C.
AaB
D.
abb
Correct Answer:
AAbb
Explanation:
AAbb contains two complete gene-pair genotypes, AA and bb, and is one of the nine possible genotypic classes in the dihybrid F2 generation.
4. In the cross AaBb × AaBb, what fraction of the offspring is expected to have the genotype AABB?
A.
1/4
B.
1/8
C.
1/16
D.
3/16
Correct Answer:
1/16
Explanation:
The probability of AA is 1/4 and the probability of BB is 1/4. By independent assortment, the probability of AABB is 1/4 × 1/4 = 1/16.
5. In a dihybrid cross AaBb × AaBb, which genotype has the highest frequency?
A.
AABB
B.
AaBb
C.
AAbb
D.
aabb
Correct Answer:
AaBb
Explanation:
The genotype Aa occurs with probability 1/2 and Bb also occurs with probability 1/2. Thus, AaBb has a probability of 1/2 × 1/2 = 1/4, the highest among the genotypic classes.
6. How many genotypic classes in the F2 generation of AaBb × AaBb contain at least one homozygous gene pair?
A.
3
B.
5
C.
8
D.
9
Correct Answer:
8
Explanation:
There are 9 total genotypic classes. Only AaBb is heterozygous at both loci, so the remaining 8 classes contain at least one homozygous gene pair.
7. Which genotype occurs with a frequency of 1/8 in the cross AaBb × AaBb?
A.
AABB
B.
AaBb
C.
AABb
D.
aabb
Correct Answer:
AABb
Explanation:
The probability of AA is 1/4 and the probability of Bb is 1/2. Therefore, the probability of AABb is 1/4 × 1/2 = 1/8.
8. Which genotype occurs in the same proportion as AAbb in the cross AaBb × AaBb?
A.
AaBb
B.
AABb
C.
Aabb
D.
aabb
Correct Answer:
aabb
Explanation:
AAbb has a probability of 1/4 × 1/4 = 1/16. The genotype aabb also has a probability of 1/4 × 1/4 = 1/16.
9. In the F2 generation of AaBb × AaBb, how many offspring genotypic classes are heterozygous at both loci?
A.
1
B.
2
C.
4
D.
9
Correct Answer:
1
Explanation:
Only the genotype AaBb is heterozygous at both loci, so there is one such genotypic class.
10. What is the probability of obtaining the genotype AaBB from the cross AaBb × AaBb?
A.
1/16
B.
1/8
C.
1/4
D.
3/8
Correct Answer:
1/8
Explanation:
The probability of Aa is 1/2 and the probability of BB is 1/4. Therefore, the probability of AaBB is 1/2 × 1/4 = 1/8.
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