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Heredity & Genetics — Homi Bhabha Exam Biology MCQs with Solutions
Free Homi Bhabha Exam Biology Heredity & Genetics MCQs with step-by-step solutions covering DNA/RNA Structure, Mendel's Laws of Inheritance, Genetic Variation. Practise online on Prepizo — no login needed.
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Sample questions with solutions
Q1 — DNA/RNA Structure · hard · theory
The double-helix structure of DNA was proposed by:
A. Darwin
B. Watson and Crick ✓ Correct
C. Mendel
D. Robert Hooke
Solution: James Watson and Francis Crick described the DNA double helix in 1953.
Q2 — DNA/RNA Structure · hard · theory
In RNA, the base that replaces thymine (found in DNA) is:
A. cytosine
B. guanine
C. uracil ✓ Correct
D. adenine
Solution: RNA uses uracil (U) in place of the thymine found in DNA.
Q3 — DNA/RNA Structure · hard · theory
In the DNA double helix, adenine (A) always pairs with:
A. uracil (U)
B. cytosine (C)
C. guanine (G)
D. thymine (T) ✓ Correct
Solution: Complementary base pairing: A pairs with T, and G pairs with C.
Q4 — DNA/RNA Structure · hard · theory
Structurally, DNA is usually ______, while RNA is usually ______:
A. both double-stranded
B. both single-stranded
C. single-stranded; double-stranded
D. double-stranded; single-stranded ✓ Correct
Solution: DNA is typically a double-stranded helix; RNA is generally single-stranded.
Q5 — DNA/RNA Structure · hard · theory
A single unit (building block) of DNA, consisting of a sugar, a phosphate and a base, is called a:
A. monosaccharide
B. nucleotide ✓ Correct
C. amino acid
D. fatty acid
Solution: A nucleotide (sugar + phosphate + nitrogenous base) is the monomer of nucleic acids.
Q6 — Mendel's Laws of Inheritance · hard · theory
A trait that appears in the first generation (F₁) and masks the other is called:
A. acquired
B. dominant ✓ Correct
C. recessive
D. hybrid
Solution: The dominant trait is expressed in the F₁ generation, masking the recessive one.
Q7 — Mendel's Laws of Inheritance · hard · theory
When a pure tall pea plant (TT) is crossed with a pure dwarf plant (tt), the F₁ offspring are all:
A. medium height
B. tall (Tt) ✓ Correct
C. half tall, half dwarf
D. dwarf (tt)
Solution: All F₁ plants are Tt and appear tall, since tallness (T) is dominant.
Q8 — Mendel's Laws of Inheritance · hard · theory
In Mendel's monohybrid cross, the phenotypic ratio obtained in the F₂ generation is:
A. 2 : 1
B. 1 : 1
C. 3 : 1 ✓ Correct
D. 9 : 3 : 3 : 1
Solution: Self-pollinating the F₁ (Tt) gives a 3 : 1 ratio of dominant to recessive in F₂.
Q9 — Mendel's Laws of Inheritance · hard · theory
The observable characteristics of an organism (e.g. its height or flower colour) are called its:
A. chromosome
B. phenotype ✓ Correct
C. genotype
D. allele
Solution: Phenotype refers to the visible traits produced by the genotype and environment.
Q10 — Mendel's Laws of Inheritance · hard · theory
A plant with the genotype Tt is described as:
A. heterozygous (hybrid) tall ✓ Correct
B. pure dwarf
C. homozygous tall
D. homozygous dwarf
Solution: Tt has two different alleles, so it is heterozygous (a hybrid), and it appears tall.
Q11 — Mendel's Laws of Inheritance · hard · theory
Mendel's law of segregation states that during gamete formation, the two alleles of a trait:
A. separate so that each gamete gets only one ✓ Correct
B. both go into every gamete
C. disappear
D. always stay together
Solution: Each gamete receives only one allele of a gene, which recombine at fertilisation.
Q12 — Genetic Variation · hard · theory
Which type of reproduction generally produces MORE variation among offspring?
A. sexual reproduction ✓ Correct
B. budding
C. asexual reproduction
D. binary fission
Solution: Sexual reproduction mixes genes from two parents, producing greater variation.
Q13 — Genetic Variation · hard · theory
A sudden, permanent change in the gene (DNA) of an organism is called a:
A. adaptation
B. reproduction
C. mutation ✓ Correct
D. variation only
Solution: A mutation is a change in the DNA that can create new variations.
Q14 — Genetic Variation · hard · theory
A human female has the sex chromosomes ______ and a male has ______:
A. XX; XX
B. XX; XY ✓ Correct
C. XY; XX
D. XY; XY
Solution: Females are XX and males are XY.
Q15 — Genetic Variation · hard · theory
The sex of a human child is determined by the:
A. temperature
B. father (whether the sperm carries X or Y) ✓ Correct
C. mother only
D. both equally at random
Solution: The mother always gives X; the father's sperm (X or Y) decides whether the child is a girl (XX) or boy (XY).
Q16 — Genetic Variation · hard · theory
A trait developed during an individual's lifetime (like a scar or learned skill) is:
A. a mutation
B. an inherited trait
C. an acquired trait that is not inherited ✓ Correct
D. always passed to offspring
Solution: Acquired traits arise from the environment and are not passed on to offspring genetically.
Q17 — DNA/RNA Structure · medium · theory
The molecule that carries the hereditary (genetic) information in most living organisms is:
A. RNA only
B. protein
C. DNA ✓ Correct
D. glucose
Solution: DNA (deoxyribonucleic acid) stores and transmits genetic information.
Q18 — DNA/RNA Structure · medium · theory
The four nitrogenous bases found in DNA are adenine, thymine, guanine and:
A. ribose
B. cytosine ✓ Correct
C. glucose
D. uracil
Solution: DNA contains A, T, G and C; uracil occurs in RNA, not DNA.
Q19 — DNA/RNA Structure · medium · theory
A segment of DNA that controls a particular trait is called a:
A. ribosome
B. gene ✓ Correct
C. tissue
D. cell
Solution: A gene is a unit of heredity — a stretch of DNA coding for a characteristic.
Q20 — DNA/RNA Structure · medium · theory
The thread-like structures in the nucleus that carry the genes are called:
A. lysosomes
B. chromosomes ✓ Correct
C. vacuoles
D. ribosomes
Solution: Chromosomes, made of DNA and protein, carry the genes.
Q21 — DNA/RNA Structure · medium · theory
In eukaryotic cells, most of the DNA is located in the:
A. cytoplasm
B. cell wall
C. ribosome
D. nucleus ✓ Correct
Solution: The bulk of a eukaryotic cell's DNA is found in the nucleus (some in mitochondria/chloroplasts).
Q22 — Mendel's Laws of Inheritance · medium · theory
The scientist regarded as the "Father of Genetics", who worked on pea plants, is:
A. Watson
B. Gregor Mendel ✓ Correct
C. Louis Pasteur
D. Charles Darwin
Solution: Gregor Mendel established the laws of inheritance through experiments on garden pea plants.
Q23 — Mendel's Laws of Inheritance · medium · theory
A trait that remains hidden in the F₁ generation is called:
A. mutant
B. acquired
C. recessive ✓ Correct
D. dominant
Solution: The recessive trait does not appear in F₁ but can reappear later.
Q24 — Mendel's Laws of Inheritance · medium · theory
The genetic makeup of an organism (e.g. Tt) is called its:
A. chromosome
B. phenotype
C. genotype ✓ Correct
D. gene pool
Solution: Genotype is the set of alleles (e.g. Tt); phenotype is the visible expression.
Q25 — Mendel's Laws of Inheritance · medium · theory
Mendel chose the garden pea for his experiments partly because it has:
A. clearly contrasting characters and a short life cycle ✓ Correct
B. no seeds
C. no flowers
D. a very long life cycle
Solution: Pea plants show clear contrasting traits, are easy to cross and grow quickly.
Q26 — Genetic Variation · medium · theory
The differences seen among individuals of the same species are called:
A. clones
B. variations ✓ Correct
C. mutations only
D. traits
Solution: Variations are the differences in characteristics among individuals of a species.
Q27 — Genetic Variation · medium · theory
Variations are important because they:
A. help a species adapt and survive in changing conditions ✓ Correct
B. reduce survival
C. always harm the organism
D. stop evolution
Solution: Useful variations improve the chances of survival and are the raw material for evolution.
Q28 — Genetic Variation · medium · theory
In human beings, the total number of chromosomes in a body cell is:
A. 46 (23 pairs) ✓ Correct
B. 23
C. 48
D. 44
Solution: Humans have 46 chromosomes arranged in 23 pairs.
Q29 — Genetic Variation · medium · theory
Traits that are passed from parents to offspring through genes are called:
A. learned traits
B. inherited traits ✓ Correct
C. acquired traits
D. temporary traits
Solution: Inherited (genetic) traits are transmitted through genes to the next generation.
Q30 — Genetic Variation · medium · theory
Variation ultimately provides the basis for the process of:
A. evolution ✓ Correct
B. digestion
C. excretion
D. respiration
Solution: Variations, acted on by natural selection, drive the evolution of species over time.