Learn › Homi Bhabha Class 9 · Biology › Heredity & Genetics
Heredity & Genetics — Homi Bhabha Class 9 Biology MCQs with Solutions
Free Homi Bhabha Class 9 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.
▶ Practise Heredity & Genetics online (free)
Subtopics
Sample questions with solutions
Q1 — DNA/RNA Structure · easy · theory
What does the abbreviation DNA stand for?
A. Dinucleic ribose acid
B. Diribonucleic acid
C. Deoxyribonucleic acid ✓ Correct
D. Deoxyribose amino acid
Solution: DNA stands for Deoxyribonucleic acid, the molecule that carries genetic information. The "deoxy" refers to its sugar (deoxyribose), which lacks one oxygen compared with ribose.
Q2 — DNA/RNA Structure · easy · theory
Which sugar is present in a molecule of RNA?
A. Sucrose
B. Deoxyribose
C. Ribose ✓ Correct
D. Glucose
Solution: RNA contains the five-carbon sugar ribose. DNA contains deoxyribose, which has one fewer oxygen atom. This difference in sugar is one of the main ways DNA and RNA differ.
Q3 — DNA/RNA Structure · easy · theory
In a DNA molecule, the base adenine (A) always pairs with which base?
A. Cytosine (C)
B. Thymine (T) ✓ Correct
C. Uracil (U)
D. Guanine (G)
Solution: By complementary base pairing, adenine pairs with thymine (A-T) and guanine pairs with cytosine (G-C). Uracil replaces thymine only in RNA, not in DNA.
Q4 — Mendel's Laws of Inheritance · easy · theory
Gregor Mendel carried out his famous inheritance experiments using which plant?
A. Rose
B. Maize
C. Garden pea ✓ Correct
D. Sunflower
Solution: Mendel used the garden pea (Pisum sativum). It was ideal because it has clear contrasting traits, is easy to grow, and can be both self-pollinated and cross-pollinated in a controlled way.
Q5 — Mendel's Laws of Inheritance · easy · theory
An organism that carries two identical alleles for a trait (for example TT or tt) is said to be:
A. Codominant
B. Recessive-only
C. Homozygous ✓ Correct
D. Heterozygous
Solution: Two identical alleles (TT or tt) make an organism homozygous for that trait. When the two alleles are different (Tt), the organism is heterozygous.
Q6 — Genetic Variation · easy · theory
Which type of reproduction generally produces offspring with more genetic variation?
A. Binary fission
B. Sexual reproduction ✓ Correct
C. Asexual reproduction
D. Budding
Solution: Sexual reproduction mixes genes from two parents (through gamete formation and fertilisation), so it produces offspring that differ from each other. Asexual methods such as budding and binary fission give near-identical copies.
Q7 — 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.
Q8 — 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.
Q9 — 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.
Q10 — 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.
Q11 — 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.
Q12 — 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.
Q13 — 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.
Q14 — 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.
Q15 — 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.
Q16 — 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.
Q17 — 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.
Q18 — 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.
Q19 — 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.
Q20 — 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.
Q21 — 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).
Q22 — 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.
Q23 — DNA/RNA Structure · hard · numerical
A double-stranded DNA molecule has 200 base pairs, of which 60 are adenine-thymine (A-T) pairs. Each A-T pair has 2 hydrogen bonds and each guanine-cytosine (G-C) pair has 3. How many hydrogen bonds hold the whole molecule together?
A. 600
B. 400
C. 460
D. 540 ✓ Correct
Solution: A-T pairs = 60, giving 60 × 2 = 120 bonds. G-C pairs = 200 - 60 = 140, giving 140 × 3 = 420 bonds. Total = 120 + 420 = 540 hydrogen bonds.
Q24 — DNA/RNA Structure · hard · theory
In the DNA double helix a purine always pairs with a pyrimidine (A with T, G with C). What is the main structural reason for this specific pairing?
A. It removes the need for hydrogen bonds
B. It makes the two strands run in the same direction
C. It keeps the width of the double helix uniform along its length ✓ Correct
D. It converts deoxyribose into ribose
Solution: A purine (larger, two rings) pairs with a pyrimidine (smaller, one ring). This always gives the same combined width, so the two strands stay a constant distance apart and the helix has a uniform diameter throughout.
Q25 — Mendel's Laws of Inheritance · hard · numerical
In a dihybrid cross between plants heterozygous for both seed shape and seed colour (RrYy × RrYy), 1600 offspring are produced. About how many are expected to show both recessive traits (wrinkled and green)?
A. 100 ✓ Correct
B. 300
C. 900
D. 400
Solution: In a dihybrid F2 the phenotypic ratio is 9 : 3 : 3 : 1, so the double-recessive class is 1/16 of the offspring. 1/16 × 1600 = 100 plants. (900 would be the double-dominant 9/16 group.)
Q26 — Mendel's Laws of Inheritance · hard · theory
A tall pea plant is crossed with a short (tt) plant. The offspring are about one-half tall and one-half short. What is the genotype of the tall parent?
A. tt (homozygous recessive)
B. A tall plant cannot give any short offspring
C. TT (homozygous dominant)
D. Tt (heterozygous) ✓ Correct
Solution: This is a test cross. If the tall parent were TT, all offspring would be tall. A 1 tall : 1 short ratio means the tall parent must carry a hidden recessive allele, so its genotype is Tt (heterozygous).
Q27 — Genetic Variation · hard · theory
Two farmers grow the same crop. Farmer A propagates plants only by cuttings (asexually), while Farmer B grows them from seeds produced by cross-pollination. If a new disease strikes, whose field is more likely to contain at least some resistant plants, and why?
A. Farmer A, because genetically identical plants always resist disease
B. Farmer B, because sexual reproduction creates more genetic variation among the plants ✓ Correct
C. Both equally, because variation does not affect disease resistance
D. Neither, because disease resistance can never be inherited
Solution: Farmer A's plants are genetic copies, so if one is susceptible all are. Farmer B's seed-grown plants vary genetically, so some individuals are more likely to carry resistance and survive the disease.
Q28 — Genetic Variation · hard · theory
Assertion (A): Genetic variation within a species is important for evolution. Reason (R): Natural selection acts on the variation present in a population, favouring individuals better suited to the environment. Choose the correct option.
A. Both A and R are true, but R is not the correct explanation of A
B. A is false but R is true
C. A is true but R is false
D. Both A and R are true, and R is the correct explanation of A ✓ Correct
Solution: Both statements are true. Evolution needs variation to work on, and natural selection is exactly the process that acts on that variation, favouring better-suited individuals. So R correctly explains why variation matters for evolution.
Q29 — 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.
Q30 — 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.