biology : class12 Parental Genotype Selection : Dihybrid Cross, Independent Assortment : Law of Independent Assortment MCQ Questions and Answers
Practice important
Parental Genotype Selection
MCQ questions and answers.
Page 1
of
1
|
10
MCQ Questions
1. In a dihybrid cross involving independently assorting genes A/a and B/b, which parental genotypes must be selected to obtain an F1 generation in which every offspring is AaBb?
A.
AABB × aabb
B.
AAbb × aaBB
C.
AABB × aaBb
D.
AaBB × aabb
Correct Answer:
AABB × aabb
Explanation:
A homozygous dominant parent produces only AB gametes, while an aabb parent produces only ab gametes. Their union therefore gives AaBb in every F1 offspring.
2. To produce an F1 generation consisting entirely of double-recessive individuals aabb, which parental cross should be selected?
A.
AABB × aabb
B.
AAbb × aaBB
C.
Aabb × aabb
D.
AaBb × aabb
Correct Answer:
Aabb × aabb
Explanation:
The aabb parent always contributes ab. The Aabb parent produces Ab and ab gametes, so the progeny are Aabb and aabb rather than all aabb. Therefore this option is not correct.
3. Which cross is required if the objective is to generate an F1 generation with all offspring having genotype AaBb, but the two loci must originate from opposite homozygous parents?
A.
AABB × aabb
B.
AAbb × aaBB
C.
AABb × aabb
D.
AaBB × aaBb
Correct Answer:
AAbb × aaBB
Explanation:
AAbb produces only Ab gametes and aaBB produces only aB gametes. Every zygote is therefore AaBb, with dominant alleles contributed in opposite phase by the two parents.
4. For a dihybrid testcross intended to reveal the gametes of an individual with unknown genotype at both loci, which parental genotype should be selected as the tester?
A.
AABB
B.
AAbb
C.
aaBB
D.
aabb
Correct Answer:
aabb
Explanation:
An aabb tester contributes only ab gametes. Consequently, each offspring genotype directly reflects the gamete contributed by the unknown parent, making it the appropriate tester for both genes.
5. A breeder wants the F1 generation to show the classical 9:3:3:1 phenotypic ratio for two independently assorting genes with complete dominance. Which parental genotypes should be crossed?
A.
AABB × aabb
B.
AAbb × aaBB
C.
AaBb × AaBb
D.
AaBb × aabb
Correct Answer:
AaBb × AaBb
Explanation:
The 9:3:3:1 ratio is produced when both parents are heterozygous for both genes. Each AaBb parent forms AB, Ab, aB, and ab gametes in equal proportions.
6. Which parental cross produces an F1 generation with a 1:1 phenotypic ratio for the A locus while all offspring are phenotypically dominant for B, assuming complete dominance?
A.
AaBB × aaBB
B.
AaBb × aabb
C.
AABb × aaBB
D.
AAbb × aaBb
Correct Answer:
AaBB × aaBB
Explanation:
At the A locus, Aa × aa gives one-half Aa and one-half aa, producing a 1:1 dominant-to-recessive ratio. At the B locus, BB × BB makes every offspring BB and therefore B-dominant.
7. A researcher needs an F1 generation in which the A locus is uniformly heterozygous, whereas the B locus segregates in a 1:1 ratio between BB and Bb. Which cross should be selected?
A.
AABB × aaBb
B.
AaBB × Aabb
C.
AAbb × aaBB
D.
AaBb × aabb
Correct Answer:
AABB × aaBb
Explanation:
The AABB parent contributes AB exclusively, and the aaBb parent contributes aB or ab. All offspring receive A from one parent and a from the other, making them Aa; the B locus becomes BB or Bb in equal proportions.
8. Which cross should be chosen to obtain an F1 generation with four genotypic classes in equal proportions, while using one parent that is homozygous recessive at both loci?
A.
AABB × aabb
B.
AaBb × aabb
C.
AABb × aabb
D.
AaBB × aabb
Correct Answer:
AaBb × aabb
Explanation:
AaBb produces AB, Ab, aB, and ab gametes equally under independent assortment. Since aabb contributes only ab, the offspring AaBb, Aabb, aaBb, and aabb occur in equal proportions.
9. A desired F1 individual must be heterozygous at A but homozygous recessive at B. Which cross guarantees that every offspring has genotype Aabb?
A.
AAbb × aabb
B.
AAbb × aaBB
C.
AaBB × aabb
D.
Aabb × Aabb
Correct Answer:
AAbb × aabb
Explanation:
AAbb produces only Ab gametes and aabb produces only ab gametes. Every offspring consequently receives A from the first parent, a from the second, and b from both parents, giving Aabb.
10. To obtain an F1 generation in which all offspring are phenotypically dominant for A but segregate 1:1 for the B phenotype, which parental genotypes are most appropriate?
A.
AABB × aaBb
B.
AaBB × aabb
C.
AABb × aabb
D.
AAbb × aaBb
Correct Answer:
AABb × aabb
Explanation:
AABb produces AB and Ab gametes, while aabb produces only ab. All offspring receive A from the first parent and a from the second, so all are A-dominant; the B locus gives Bb and bb in a 1:1 ratio.
Short Questions and Answers
Practice short questions and answers related to
Parental Genotype Selection
.
Short questions are currently unavailable for this page.