Free NEET Biology practice
Principles of Inheritance and Variation: MCQs with Solutions
Write parental genotypes and possible gametes before predicting offspring. These original questions state the inheritance assumptions explicitly: complete dominance where specified, equal gamete probabilities, and independent assortment only when the genes are unlinked.
5 original practice questions — not previous-year paper reproductions. No account required.
By NEET Ninja · Updated
Before you answer
- Genotype describes the alleles present; phenotype describes the expressed trait. A 1:2:1 genotype ratio can produce a 3:1 phenotype ratio under complete dominance.
- A test cross pairs an individual with the dominant phenotype with a homozygous recessive individual to help infer the unknown genotype.
- Independent assortment requires the appropriate gene relationship. Do not apply a dihybrid ratio to linked genes without considering recombination.
Questions and worked answers
Choose an option before reading the answer. For a wrong answer, identify the step or concept that changed the result.
QUESTION 1
In an Aa × Aa cross with complete dominance of A, what is the expected phenotypic ratio?
- 1 dominant : 1 recessive
- 3 dominant : 1 recessive
- 1 dominant : 3 recessive
- All dominant
Answer: B — 3 dominant : 1 recessive
Each parent produces A and a gametes with equal probability. The offspring genotypes are AA, Aa, Aa, and aa in a 1:2:1 ratio. Under complete dominance, AA and Aa show the dominant phenotype, giving an expected dominant:recessive ratio of 3:1.
QUESTION 2
What is the expected genotype ratio from the test cross Aa × aa?
- 1 AA : 1 aa
- 3 Aa : 1 aa
- 1 Aa : 1 aa
- All Aa
Answer: C — 1 Aa : 1 aa
The heterozygous parent produces A and a gametes equally, while the homozygous recessive parent produces only a gametes. Their combinations give Aa and aa with equal probability. The expected genotype ratio is therefore 1:1, not the 3:1 phenotype ratio of Aa × Aa.
QUESTION 3
For an individual AaBb with unlinked genes and normal segregation, what is the probability of an ab gamete?
- 1/2
- 1/4
- 1/8
- 1
Answer: B — 1/4
The probability of receiving a is 1/2 and the probability of receiving b is 1/2. With independent assortment, multiply the probabilities: (1/2) × (1/2) = 1/4. The four gamete types AB, Ab, aB, and ab are equally likely under these assumptions.
QUESTION 4
In a flower species with incomplete dominance, RR is red, rr is white, and Rr is pink. What is the expected phenotype ratio from Rr × Rr?
- 3 red : 1 white
- All pink
- 1 red : 2 pink : 1 white
- 1 red : 1 white
Answer: C — 1 red : 2 pink : 1 white
The cross gives genotypes RR, Rr, Rr, and rr in a 1:2:1 ratio. Because the heterozygote has its own intermediate phenotype, each genotype class is distinguishable: one red, two pink, and one white. Complete dominance is not assumed, so a 3:1 ratio does not apply.
QUESTION 5
Which statement correctly describes the Iᴬ and Iᴮ alleles in a person with AB blood group?
- Iᴬ is completely dominant over Iᴮ
- Iᴮ is completely dominant over Iᴬ
- Both are expressed codominantly
- Both are recessive to i in this genotype
Answer: C — Both are expressed codominantly
In the IᴬIᴮ genotype, both alleles are expressed and both A and B antigens are present on red blood cells. This is codominance, not blending into an intermediate antigen. Each of these alleles is dominant over i, but the i allele is not present in the AB genotype.
Study source and corrections
Use the matching chapter in NCERT Class XII Biology — Principles of Inheritance and Variation for the underlying concepts. These questions are written for NEET Ninja, not endorsed or supplied by NCERT or NTA.
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