NEET 2025 MCQ with Answer Explanation : “Inheritance Chapter”.

71. Which of the following is a characteristic feature of Turner syndrome?
    a) Extra X chromosome in males
    b) Trisomy 21
    c) Missing X chromosome in females
    d) Trisomy 13

Answer: (c) Missing X chromosome in females

Explanation: Turner syndrome occurs when a female is missing one of her X chromosomes (45, X instead of 46, XX). Individuals with this condition often have short stature, delayed puberty, and infertility. Other choices represent different chromosomal disorders: Klinefelter syndrome (extra X chromosome in males), Down syndrome (trisomy 21), and Patau syndrome (trisomy 13).

72. Which of the following is the expected phenotypic ratio for a monohybrid cross involving incomplete dominance?
    a) 3:1
    b) 9:3:3:1
    c) 1:2:1
    d) 1:1:1:1

Answer: (c) 1:2:1

Explanation: In incomplete dominance, the heterozygous phenotype is a blend of the two homozygous phenotypes. A cross between two heterozygous individuals (e.g., Rr) results in a 1:2:1 ratio: 1 showing the dominant phenotype, 2 showing the intermediate (heterozygous) phenotype, and 1 showing the recessive phenotype.

73. The process of RNA synthesis from a DNA template is called:
    a) Translation
    b) Transcription
    c) Replication
    d) Reverse transcription

Answer: (b) Transcription

Explanation: Transcription is the process by which RNA is synthesized from a DNA template. During this process, RNA polymerase reads the DNA sequence and synthesizes a complementary strand of messenger RNA (mRNA). Translation is the process where mRNA is used to synthesize proteins.

74. In the lac operon of E. coli, what is the role of the lac repressor protein?
    a) It promotes the transcription of the lac operon genes
    b) It inhibits the transcription of the lac operon genes
    c) It binds to lactose to initiate transcription
    d) It degrades lactose

Answer: (b) It inhibits the transcription of the lac operon genes

Explanation: The lac repressor protein binds to the operator region of the lac operon, preventing RNA polymerase from transcribing the genes necessary for lactose metabolism. When lactose is present, it binds to the repressor, causing it to release from the operator, allowing transcription to occur.

75. A gene located on the X chromosome is referred to as:
    a) Autosomal
    b) X-linked
    c) Y-linked
    d) Homologous

Answer: (b) X-linked

Explanation: Genes located on the X chromosome are called X-linked genes. Males have only one X chromosome, so a single copy of a recessive allele on the X chromosome can cause an X-linked disorder, such as color blindness or hemophilia. Females have two X chromosomes, so they can be carriers if only one X chromosome has the mutation.

76. Which of the following genetic disorders is caused by a frameshift mutation?
    a) Sickle cell anemia
    b) Huntington’s disease
    c) Cystic fibrosis
    d) Tay-Sachs disease

Answer: (d) Tay-Sachs disease

Explanation: Tay-Sachs disease is caused by a frameshift mutation in the HEXA gene, leading to a defective enzyme (hexosaminidase A) that results in the accumulation of harmful substances in the nervous system. Frameshift mutations involve insertions or deletions of nucleotides that alter the reading frame of the genetic code, severely affecting protein function.

77. If two carriers for an autosomal recessive genetic disorder (Aa x Aa) have children, what is the probability that their child will be affected?
    a) 100%
    b) 50%
    c) 25%
    d) 75%

Answer: (c) 25%

Explanation: In an autosomal recessive inheritance pattern, both parents must carry one copy of the mutated gene (Aa). When two heterozygotes mate, there is a 25% chance (aa) that their offspring will inherit two copies of the recessive allele and express the disorder, a 50% chance (Aa) that they will be carriers, and a 25% chance (AA) of being unaffected.

78. Which process explains why children inherit half of their genetic information from each parent?
    a) Mitosis
    b) Fertilization
    c) Meiosis
    d) Crossing over

Answer: (c) Meiosis

Explanation: Meiosis is the process that reduces the chromosome number by half, producing gametes (sperm and eggs) with 23 chromosomes each in humans. During fertilization, the gametes from both parents combine to form a zygote with 46 chromosomes (half from each parent). This ensures that offspring inherit genetic information from both parents.

79. Which of the following is an example of codominance in humans?
    a) ABO blood groups
    b) Skin color
    c) Eye color
    d) Height

Answer: (a) ABO blood groups

Explanation: In codominance, both alleles are expressed equally in the phenotype. The ABO blood group system is a classic example where both IA and IB alleles are expressed equally in individuals with the AB blood type. Skin color and height are examples of polygenic traits, and eye color involves simple dominance.

80. In Hardy-Weinberg equilibrium, if the frequency of the recessive allele (q) is 0.3, what is the frequency of homozygous dominant individuals?
    a) 0.09
    b) 0.49
    c) 0.42
    d) 0.21

Answer: (b) 0.49

Explanation: The Hardy-Weinberg equation is p² + 2pq + q² = 1, where p is the frequency of the dominant allele and q is the frequency of the recessive allele. If q = 0.3, then p = 1 – 0.3 = 0.7. The frequency of homozygous dominant individuals is p² = 0.7² = 0.49.