1. What is the genotypic ratio obtained from a cross between two individuals with genotype AaBb?
A.
1:1:1:1
B.
9:3:3:1
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 self-cross AaBb × AaBb produces nine genotype classes in the ratio 1:2:1:2:4:2:1:2:1.
2. In the cross AaBb × AaBb, what is the proportion of offspring with genotype AABB?
A.
1/16
B.
2/16
C.
4/16
D.
9/16
Correct Answer:
1/16
Explanation:
AABB occurs once among the 16 possible offspring combinations, so its proportion is 1/16.
3. In the dihybrid cross AaBb × AaBb, which genotype occurs in the greatest proportion?
A.
AABB
B.
AaBb
C.
AAbb
D.
aabb
Correct Answer:
AaBb
Explanation:
The heterozygous genotype AaBb occurs 4 times out of 16, which is the highest frequency in the dihybrid genotypic ratio.
4. What is the genotypic ratio for the gene pair A in the cross AaBb × AaBb?
A.
1 AA : 2 Aa : 1 aa
B.
3 AA : 1 aa
C.
1 AA : 1 Aa : 1 aa
D.
2 AA : 1 Aa : 2 aa
Correct Answer:
1 AA : 2 Aa : 1 aa
Explanation:
For each gene pair in the dihybrid self-cross, the genotypic ratio is 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.
5. In AaBb × AaBb, what fraction of offspring have genotype AABb?
A.
1/16
B.
2/16
C.
4/16
D.
6/16
Correct Answer:
2/16
Explanation:
The genotype AABb appears 2 times among the 16 possible genotype combinations, giving a fraction of 2/16.
6. Which genotype represents a double homozygous recessive individual in a dihybrid cross?
A.
AABB
B.
AaBb
C.
Aabb
D.
aabb
Correct Answer:
aabb
Explanation:
The genotype aabb has two recessive alleles at both gene loci and is the double homozygous recessive genotype.
7. In the cross AaBb × AaBb, how many out of 16 offspring are expected to have genotype AaBB?
A.
1
B.
2
C.
4
D.
8
Correct Answer:
2
Explanation:
AaBB has a frequency of 2/16 in the dihybrid genotypic ratio, so 2 of 16 offspring are expected to have this genotype.
8. What is the frequency of genotype AAbb in the cross AaBb × AaBb?
A.
1/16
B.
2/16
C.
4/16
D.
6/16
Correct Answer:
2/16
Explanation:
AAbb occurs with a frequency of 2/16 in the genotypic ratio of the AaBb × AaBb cross.
9. How many different genotypes are produced in the cross AaBb × AaBb?
A.
4
B.
6
C.
9
D.
16
Correct Answer:
9
Explanation:
Each gene pair produces 3 genotypes, so two independently assorting gene pairs produce 3 × 3 = 9 different genotypes.
10. In the genotypic ratio 1:2:1:2:4:2:1:2:1 from AaBb × AaBb, what does the value 4 represent?
A.
The number of AABB offspring
B.
The number of AaBb offspring out of 16
C.
The number of aabb offspring
D.
The total number of genotype classes
Correct Answer:
The number of AaBb offspring out of 16
Explanation:
The central value 4 in the ratio represents the four AaBb offspring expected among 16 total offspring.
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