Free Mock Test 2026
Free NEET Principles of Inheritance Important MCQs Practice Test — Practice Questions
1. Alfred Sturtevant used the frequency of recombination between pairs of genes on the same chromosome to:
- (A) Show that genes are made of DNA
- (B) Map the relative positions of genes on a chromosome
- (C) Prove independent assortment
- (D) Discover sex linkage
Answer: (B) Map the relative positions of genes on a chromosome
Recombination frequency reflects the distance between genes. Sturtevant used it to prepare genetic maps.
2. Phenylketonuria is caused by a single gene mutation, yet it affects mental development and also hair and skin pigmentation. This is an example of:
- (A) Codominance
- (B) Epistasis
- (C) Polygenic inheritance
- (D) Pleiotropy
Answer: (D) Pleiotropy
When a single gene produces more than one phenotypic effect, it is called pleiotropy.
3. Which of the following is an autosomal recessive trait?
- (A) Phenylketonuria
- (B) Haemophilia
- (C) Colour blindness
- (D) Down's syndrome
Answer: (A) Phenylketonuria
Phenylketonuria is autosomal recessive. Haemophilia and colour blindness are X-linked recessive, and Down's syndrome is a chromosomal disorder.
4. The ABO blood group gene I has how many alleles, and how many genotypes are possible in a population?
- (A) 3 alleles and 6 genotypes
- (B) 2 alleles and 3 genotypes
- (C) 3 alleles and 3 genotypes
- (D) 4 alleles and 6 genotypes
Answer: (A) 3 alleles and 6 genotypes
The alleles are Iᴬ, Iᴮ and i. The genotypes are IᴬIᴬ, Iᴬi, IᴮIᴮ, Iᴮi, IᴬIᴮ and ii.
5. A dihybrid cross between two RrYy plants gives how many different genotypes and phenotypes in the F2?
- (A) 4 genotypes and 9 phenotypes
- (B) 9 genotypes and 4 phenotypes
- (C) 8 genotypes and 4 phenotypes
- (D) 9 genotypes and 2 phenotypes
Answer: (B) 9 genotypes and 4 phenotypes
The F2 shows 9 genotypes and 4 phenotypes in the ratio 9:3:3:1.
6. In sickle-cell anaemia, glutamic acid at the sixth position of the β-globin chain is replaced by:
- (A) Valine
- (B) Lysine
- (C) Alanine
- (D) Leucine
Answer: (A) Valine
A single base substitution changes the codon so that valine replaces glutamic acid. This alters the haemoglobin so that it polymerises under low oxygen.
7. In grasshoppers, sex determination is of which type?
- (A) XO type, in which the male has only one X chromosome
- (B) XY type, in which the male has X and Y
- (C) ZW type, in which the female is heterogametic
- (D) Haplo-diploid type
Answer: (A) XO type, in which the male has only one X chromosome
Grasshopper males have one X chromosome (XO) and females have XX.
8. A carrier woman for haemophilia marries a normal man. What proportion of their sons is expected to be haemophilic?
- (A) 0%
- (B) 50%
- (C) 75%
- (D) 100%
Answer: (B) 50%
The carrier mother (XᴴXʰ) passes Xʰ to half of her sons. Daughters will not be affected, but half of them are carriers.
9. Which of the following has the karyotype 47, XXY?
- (A) Turner's syndrome
- (B) Klinefelter's syndrome
- (C) Down's syndrome
- (D) Phenylketonuria
Answer: (B) Klinefelter's syndrome
Klinefelter's syndrome results from an extra X chromosome in a male. Such individuals are sterile and may show feminine development such as gynaecomastia.
10. A colour-blind man marries a woman with normal vision whose father was colour-blind. The probability that their daughter will be colour-blind is:
- (A) 0%
- (B) 25%
- (C) 50%
- (D) 100%
Answer: (C) 50%
The woman is a carrier because she inherited Xᶜ from her father. The man gives Xᶜ to every daughter, so half the daughters get Xᶜ from the mother and are colour-blind.
11. A person with AB blood group has both Iᴬ and Iᴮ alleles expressed equally. This is an example of:
- (A) Incomplete dominance
- (B) Complete dominance
- (C) Codominance
- (D) Epistasis
Answer: (C) Codominance
In codominance both alleles are fully expressed in the heterozygote. In the AB group both types of sugar polymers are present on the red cell surface.
12. A test cross is performed to determine:
- (A) The genotype of an individual showing the dominant phenotype
- (B) The number of chromosomes in the parent
- (C) Whether a trait is sex-linked
- (D) The rate of mutation
Answer: (A) The genotype of an individual showing the dominant phenotype
The individual is crossed with a homozygous recessive. All dominant offspring indicate a homozygous parent, and a 1:1 ratio indicates a heterozygous parent.
13. The law of purity of gametes (law of segregation) states that:
- (A) Alleles of different genes assort independently
- (B) The two alleles of a gene separate during gamete formation, so each gamete carries only one of them
- (C) A dominant allele always masks a recessive allele
- (D) Genes on the same chromosome are inherited together
Answer: (B) The two alleles of a gene separate during gamete formation, so each gamete carries only one of them
Alleles of a pair separate during meiosis and each gamete receives only one allele, so gametes are 'pure'.
14. In a cross between two heterozygous tall pea plants (Tt × Tt), the F2 phenotypic ratio and genotypic ratio are respectively:
- (A) 1:2:1 and 3:1
- (B) 9:3:3:1 and 1:2:1
- (C) 3:1 and 1:2:1
- (D) 1:1 and 1:1
Answer: (C) 3:1 and 1:2:1
Tt × Tt gives 1 TT : 2 Tt : 1 tt (genotypic 1:2:1). Because T is dominant, tall to dwarf is 3:1.
15. How many different types of gametes can an individual of genotype AaBbCc produce, assuming independent assortment?
- (A) 3
- (B) 4
- (C) 6
- (D) 8
Answer: (D) 8
Each heterozygous gene pair gives 2 types, so the number is 2 × 2 × 2 = 8.
16. Mendel studied how many pairs of contrasting characters in the garden pea?
- (A) 2
- (B) 4
- (C) 5
- (D) 7
Answer: (D) 7
Mendel selected 7 pairs of contrasting traits, such as tall and dwarf, and round and wrinkled seeds.
17. In birds, the heterogametic sex and its chromosome constitution are:
- (A) Male, ZW
- (B) Male, ZZ
- (C) Female, ZZ
- (D) Female, ZW
Answer: (D) Female, ZW
In birds the female is heterogametic (ZW) and the male is homogametic (ZZ).
18. The gene for β-thalassaemia is located on chromosome number:
- (A) 21
- (B) 16
- (C) 7
- (D) 11
Answer: (D) 11
The β-globin gene (HBB) is on chromosome 11. The α-globin genes are on chromosome 16.
19. The chromosomal theory of inheritance was proposed independently by:
- (A) Morgan and Bridges
- (B) Mendel and Correns
- (C) Sutton and Boveri
- (D) Watson and Crick
Answer: (C) Sutton and Boveri
Sutton and Boveri noticed that chromosome behaviour during meiosis parallels the behaviour of Mendel's factors.
20. Down's syndrome is caused by:
- (A) Absence of one X chromosome
- (B) An extra X chromosome in males
- (C) Trisomy of chromosome 21
- (D) Monosomy of chromosome 21
Answer: (C) Trisomy of chromosome 21
Down's syndrome results from three copies of chromosome 21 (total 47). Turner's syndrome is the absence of one X.