Genetics, Heredity & Biotechnology – NDA Biology PYQs

NDA 2025-I

Q. 1. Which is the correct base pairing found in a normal DNA molecule?

(a) Adenine pairs with Thymine

(b) Adenine pairs with Guanine

(c) Adenine pairs with Cytosine

(d) Thymine pairs with Guanine

Answer: (a) Adenine pairs with Thymine

Explanation: In DNA, base pairing follows Chargaff’s rules. Adenine (A) always pairs with Thymine (T) through two hydrogen bonds. Guanine (G) always pairs with Cytosine (C) through three hydrogen bonds. These are the only correct Watson-Crick base pairs. Adenine never pairs with guanine or cytosine, and thymine never pairs with guanine. The A-T and G-C pairing is the foundation of DNA replication and transcription. Concept Tested: DNA base pairing: Adenine-Thymine (A-T, 2 H-bonds) and Guanine-Cytosine (G-C, 3 H-bonds): Chargaff’s rules

★ JOVIK Exam Insight Base pairing rule mnemonic: A pairs with T (both have 2 rings? No: A has 2, T has 1). Better: ‘AT the GC Concert’: A with T, G with C. In RNA, Thymine is replaced by Uracil: so A pairs with U in RNA. G-C pairing is stronger (3 hydrogen bonds) than A-T (2 hydrogen bonds).

NDA 2023-II

Q. 2. The two important features of sexual reproduction in higher organisms that create genetic diversity in offspring are

(a) Mitosis and fertilization

(b) Meiosis and fertilization

(c) Mitosis and binary fission

(d) Meiosis and conjugation

Answer: (b) Meiosis and fertilization

Explanation: Genetic diversity in sexually reproducing organisms arises from two key events. Meiosis creates genetically diverse gametes through independent assortment of chromosomes and crossing over between homologous chromosomes. Fertilisation then combines gametes from two parents, producing unique combinations of alleles. Mitosis produces genetically identical cells. Binary fission is asexual. Conjugation is a form of gene transfer in bacteria, not in higher organisms. Concept Tested: Meiosis (crossing over, independent assortment) and fertilisation create genetic diversity in sexual reproduction

Q. 3. In a sexually reproducing organism, which one of the following statements is appropriate both for the parent and offspring?

(a) Chromosome number increases but DNA content remains constant

(b) Both chromosome number and DNA content remains constant

(c) Chromosome number decreases but DNA content remains constant

(d) Both chromosome number and DNA content decreases

Answer: (b) Both chromosome number and DNA content remains constant

Explanation: In sexually reproducing organisms, the chromosome number (2n) is maintained across generations. Meiosis halves the chromosome number (2n → n in gametes), but fertilisation restores it (n + n → 2n in zygote). The offspring, like the parent, has 2n chromosomes. Similarly, the DNA content (genome) remains constant across generations in a species. Both parent and offspring of the same species have the same chromosome number and DNA content. Concept Tested: Both chromosome number (2n) and DNA content remain constant between parent and offspring in sexually reproducing organisms

NDA 2023-I

Q. 4. One advantage of sexual reproduction over asexual reproduction is that it helps species to survive over long evolutionary time. This is because sexual reproduction produces:

(a) more offspring in each reproductive cycle.

(b) robust and healthy offspring.

(c) genetically similar offspring.

(d) more variation in offspring.

Answer: (d) more variation in offspring.

Explanation: Sexual reproduction is evolutionarily advantageous because it generates genetic variation through meiosis and fertilisation. This variation gives populations the raw material for natural selection to act upon. When environments change, some individuals with beneficial genetic combinations survive and reproduce. Asexual reproduction produces genetically identical clones: all individuals are equally vulnerable to the same threats. Sexual reproduction is slower but creates diversity that enables long-term survival. Concept Tested: Sexual reproduction creates genetic variation → raw material for natural selection → long-term species survival

NDA 2021-II

Q. 5. Different varieties of the same gene are called

(a) Genotypes

(b) Sib pairs

(c) Alleles

(d) Isomers

Answer: (c) Alleles

Explanation: Alleles are different forms (variants) of the same gene that occupy the same position (locus) on homologous chromosomes. For example, the gene for flower colour in peas can exist as a dominant allele (purple) or a recessive allele (white). Humans and most diploid organisms carry two alleles for each gene: one on each homologous chromosome. Genotype refers to the complete genetic makeup. Sib pairs are sibling pairs used in genetic studies. Isomers are chemical compounds with the same formula but different structure. Concept Tested: Alleles: different variants of the same gene at the same chromosomal locus

NDA 2017-II

Q. 6. Golden rice is a genetically-modified crop plant where the incorporated gene is meant for biosynthesis of

(a) Omega-3 fatty acids

(b) Vitamin A

(c) Vitamin B

(d) Vitamin C

Answer: (b) Vitamin A

Explanation: Golden rice is a genetically engineered variety of rice (Oryza sativa) developed to produce beta-carotene (provitamin A) in the edible portion of the grain. Normal white rice does not produce beta-carotene in the grain. The golden colour comes from the beta-carotene. Golden rice was developed to address Vitamin A deficiency in populations that depend heavily on rice as a staple food. The genes inserted are from maize (corn) and a bacterium. Concept Tested: Golden rice: GM crop producing beta-carotene (provitamin A); developed to address Vitamin A deficiency

★ JOVIK Exam Insight Golden rice = beta-carotene = Vitamin A precursor. NDA tests this as a specific biotechnology application. The golden colour is the beta-carotene itself. This was a major GM crop development involving genes from daffodil/maize for beta-carotene biosynthesis.

NDA 2016-I

Q. 7. Which of the following statements about DNA is/are correct?

1. DNA is the hereditary material of all living organisms.

2. All segments of DNA code for synthesis of proteins.

3. Nuclear DNA is double helical with two nucleotide chains which run anti-parallel.

4. DNA is also found in mitochondria.

Select the correct answer using the code given below:

(a) 1, 2 and 3 only

(b) 3 and 4 only

(c) 1, 3 and 4 only

(d) 4 only

Answer: (c) 1, 3 and 4 only

Explanation: Statement 1 is correct for cellular organisms (bacteria, plants, animals): DNA is the hereditary material. Statement 2 is incorrect: only a fraction of DNA codes for proteins. A large portion is non-coding (regulatory sequences, introns, repetitive elements). Statement 3 is correct: nuclear DNA is a double helix with two antiparallel nucleotide strands. Statement 4 is correct: DNA is found in mitochondria (and chloroplasts in plants) in addition to the nucleus. Concept Tested: DNA is double helical and antiparallel; found in nucleus and mitochondria; NOT all DNA codes for proteins

★ JOVIK Exam Insight A common NDA error is accepting ‘all DNA codes for proteins’ as true. Only 1–2% of human DNA codes for proteins. The rest includes non-coding RNA genes, regulatory sequences, repetitive DNA, and introns. This is Statement 2: it is FALSE.

NDA 2013-I

Q. 8. The sex of a newborn baby is determined by the chromosome inherited from

(a) the mother

(b) the father

(c) mother’s mother

(d) father’s father

Answer: (b) the father

Explanation: In humans, sex is determined by sex chromosomes. Females have two X chromosomes (XX). Males have one X and one Y chromosome (XY). Mothers can only donate an X chromosome in their eggs. Fathers donate either an X chromosome or a Y chromosome in their sperm. If the sperm carrying Y chromosome fertilises the egg, the offspring is male (XY). If the sperm carrying X fertilises the egg, the offspring is female (XX). The Y chromosome (from the father) determines male sex. The father’s chromosome determines the sex. Concept Tested: Sex of baby determined by father’s chromosome: X-bearing sperm → girl (XX); Y-bearing sperm → boy (XY)

★ JOVIK Exam Insight A common misconception: many people blame the mother for having sons or daughters. Scientifically, the father’s sperm determines the sex. Mothers always contribute X. Fathers contribute either X (→ girl) or Y (→ boy). This is also why sex-linked diseases like colour blindness are traced through the X chromosome from the father.

NDA 2011-II

Q. 9. With regard to animal breeding, which one among the following is not correct?

(a) In-breeding : Mating of more closely related animals within the same breed for 1 – 2 generations

(b) Out-breeding : Breeding of unrelated animals of the same breed without common ancestors for 4 – 6 generations

(c) Cross-breeding : Superior males of one breed are mated with superior females of another breed

(d) Out-crossing : Offspring is called an ‘out-cross’

Answer: (a) In-breeding : Mating of more closely related animals within the same breed for 1 – 2 generations

Explanation: Option (a) is not correct as stated. In-breeding refers to mating of closely related individuals within the same breed: this is correct. However, in-breeding is generally practised for more than just 1–2 generations to fix desirable traits. The number of generations is more variable than stated. Option (b) correctly describes out-breeding. Option (c) correctly describes cross-breeding. Option (d) is correct: the offspring of out-crossing is called an out-cross. Among the options, (a) is the least accurate description because of the restricted generation range given. Concept Tested: In animal breeding: in-breeding (related animals, same breed), out-breeding (unrelated, same breed), cross-breeding (different breeds), out-crossing (offspring = out-cross)

NDA 2010-II

Q. 10. Statement I: Human beings have 23 pair of chromosomes, one of which is the sex chromosome and the remaining 22 autosomes. The X-linked diseases are related to mutations on a sex chromosome.

Statement II: Colour blindness results from a mutation in X chromosome.

(a) Both the statements are individually true and statement II is the correct explanation of statement I

(b) Both the statements are individually true but statement II is not the correct explanation of statement I

(c) Statement I is true but statement II is false

(d) Statement I is false but statement II is true

Answer: (b) Both the statements are individually true but statement II is not the correct explanation of statement I

Explanation: Statement I is correct: humans have 23 pairs of chromosomes: 22 pairs of autosomes and 1 pair of sex chromosomes (XX or XY). X-linked diseases are caused by mutations on the X chromosome. Statement II is also correct: colour blindness is caused by a mutation in the OPN1LW or OPN1MW genes on the X chromosome. However, Statement II is not the complete explanation of Statement I: it is merely one example of an X-linked disease, not the explanation of the entire concept. Concept Tested: Both statements about sex chromosomes and colour blindness are true; Statement II is an example of, not the explanation of, Statement I

NDA 2010-I

Q. 11. Cure to spinal injury is likely to emerge from

(a) gene therapy

(b) stem cell therapy

(c) xenograft

(d) transfusion

Answer: (b) stem cell therapy

Explanation: Stem cell therapy is considered the most promising avenue for treating spinal cord injuries. Stem cells are undifferentiated cells that can differentiate into various specialised cell types, including neurons (nerve cells). Research focuses on using stem cells to regenerate damaged spinal cord tissue, restore connections between the brain and body, and repair nerve pathways. Gene therapy modifies genes. Xenografts transplant tissue across species. Transfusion transfers blood. Concept Tested: Stem cell therapy is the most promising treatment for spinal cord injuries (regeneration of nerve tissue)

NDA 2009-I

Q. 12. Which of the following are the possible blood groups of the offspring of the parents with blood group O and AB?

(a) O, A, B and AB

(b) A and B

(c) A, B and AB

(d) O and AB

Answer: (b) A and B

Explanation: Blood group O genotype = ii (no A or B antigens). Blood group AB genotype = I^A I^B. Cross: ii × I^A I^B. All offspring receive one allele from each parent. Parent O (ii) contributes only i. Parent AB (I^A I^B) contributes either I^A or I^B. Possible offspring: I^A i (blood group A) or I^B i (blood group B). No offspring will be O (requires ii) or AB (requires I^A I^B). Therefore only blood groups A and B are possible. Concept Tested: Blood group genetics: O (ii) × AB (I^A I^B) → offspring are only A (I^A i) or B (I^B i)

★ JOVIK Exam Insight Blood group Mendelian genetics: O = ii. A = I^A I^A or I^A i. B = I^B I^B or I^B i. AB = I^A I^B. Key NDA cross: O × AB gives only A and B offspring (never O or AB). This surprises many students who expect AB parents to give AB children.

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