Heredity – MCQs with Answers and Explanations
Class: CBSE Class 10
Subject: Science — Biology
Chapter: Chapter 8 — Heredity
CBSE Board Examinations
Systematic order: Syllabus → Key concepts → Topic-wise MCQs → Explanations
Instructions: 60 topic-wise multiple-choice questions with clear answers and short concept-clearing explanations. Designed strictly as per NCERT Class 10 Biology — Chapter 8: Heredity. Click "Show Answer & Explanation" under each question to reveal the correct option and concise explanation.
Basics of Heredity & Variation (Questions 1–10)
Q1.
Heredity refers to the:
Answer: B
Heredity is the passing of traits from parents to offspring via genes/chromosomes.Q2.
Which of the following best describes a gene?
Answer: B
A gene is a DNA segment (unit of heredity) arranged on chromosomes that codes for a trait.Q3.
The physical appearance of an organism is called its:
Answer: C
Phenotype is the observable trait resulting from genotype and environment.Q4.
An allele is:
Answer: A
Alleles are variant forms of the same gene at the same locus on homologous chromosomes.Q5.
Variation that shows continuous range (e.g., human height) is usually due to:
Answer: B
Polygenic traits are controlled by many genes; environment also influences continuous variation.Q6.
A mutation is best described as a:
Answer: A
Mutation is a change in DNA sequence that can create new alleles and variation.Q7.
Discrete variation is shown by:
Answer: C
Discrete traits have categories (no intermediates), e.g., purple vs white flowers in peas.Q8.
Which carries genes and ensures their transmission to offspring?
Answer: B
Chromosomes are DNA-protein structures carrying genes; they segregate during meiosis.Q9.
Which of the following is NOT a cause of variation?
Answer: D
Mitosis produces genetically identical cells and does not by itself create variation.Q10.
Which statement is true?
Answer: C
Phenotype results from genotype interacting with environment (phenotype = genotype + environment).Mendel’s Experiments & Laws (Questions 11–20)
Q11.
Gregor Mendel is famous for:
Answer: B
Mendel's controlled crosses and counting led to laws of segregation and independent assortment.Q12.
Mendel chose pea plants because:
Answer: B
Pea plants have clear contrasting traits, short generation times and controlled pollination is easy.Q13.
Mendel’s law of segregation explains:
Answer: B
Each allele pair segregates so gametes receive one allele of each gene.Q14.
In a monohybrid cross between two heterozygotes (Aa × Aa), expected phenotypic ratio is:
Answer: C
Phenotypic ratio for simple dominance in F2 is 3 (dominant):1 (recessive).Q15.
Mendel’s law of independent assortment applies when:
Answer: B
Alleles of different genes assort independently during gamete formation if genes are unlinked.Q16.
Mendel’s quantitative approach means:
Answer: A
Mendel counted many offspring and used numerical ratios to infer inheritance laws.Q17.
Pure-breeding (true-breeding) means:
Answer: B
Pure lines are homozygous and breed true for the trait.Q18.
If a cross gives an F2 phenotypic ratio of 9:3:3:1, the cross was most likely:
Answer: B
This 9:3:3:1 ratio is typical of a dihybrid cross with independent assortment.Q19.
Mendel used which trait categories in peas for study?
Answer: B
Mendel selected clear, contrasting (discrete) traits to avoid ambiguous intermediates.Q20.
Which generation refers to offspring of the parental (P) cross?
Answer: B
F1 is the first filial generation (offspring of P generation).Alleles, Dominance & Crosses (Questions 21–30)
Q21.
If T = tall and t = dwarf, cross TT × tt. What are F1 genotypes?
Answer: B
Crossing homozygous dominant with homozygous recessive yields all heterozygous (Tt) F1 offspring.Q22.
In test cross, unknown dominant phenotype is crossed with:
Answer: B
Test cross with homozygous recessive reveals whether unknown is homozygous or heterozygous based on progeny.Q23.
Genotypic ratio 1:2:1 corresponds to which cross?
Answer: B
F2 genotypic ratio of a monohybrid cross (Tt × Tt) is 1 TT : 2 Tt : 1 tt.Q24.
Incomplete dominance produces:
Answer: B
Heterozygote shows intermediate expression (e.g., pink in red × white flowers).Q25.
Co-dominance example in humans is:
Answer: B
In AB blood group, IA and IB alleles are co-dominant and both expressed.Q26.
Multiple alleles means:
Answer: B
Multiple allele systems (e.g., ABO) have more than two variants for the same gene in a population.Q27.
Which cross gives 1:1 phenotypic ratio?
Answer: C
Crossing heterozygote with homozygous recessive yields a 1:1 ratio of phenotypes.Q28.
Heterozygote showing dominant phenotype but carrying recessive allele is called:
Answer: B
Carriers are heterozygotes that carry a recessive allele without showing its phenotype.Q29.
Which ratio represents F2 genotypic distribution in monohybrid cross?
Answer: B
Monohybrid F2 genotypic ratio = 1 homozygous dominant : 2 heterozygous : 1 homozygous recessive.Q30.
Hybrid vigour (heterosis) is:
Answer: B
Heterosis describes superior qualities often seen in F1 hybrids (yield, growth).Non-Mendelian Patterns (Questions 31–38)
Q31.
ABO blood grouping is an example of:
Answer: A
ABO system displays multiple alleles (IA, IB, i) and IA & IB are co-dominant.Q32.
Pink flowers from red × white parents illustrate:
Answer: B
Incomplete dominance yields intermediate phenotype in heterozygotes (pink).Q33.
Which one is an example of polygenic inheritance?
Answer: C
Height is influenced by many genes and environment—classic polygenic trait showing continuous variation.Q34.
Genes that are close together on the same chromosome and inherited together are called:
Answer: B
Linked genes tend to be inherited together because they are physically close on a chromosome.Q35.
Recombination (crossing over) during meiosis results in:
Answer: B
Crossing over creates new allele combinations, breaking linkage at certain frequencies.Q36.
Which phenomenon explains why some dihybrid crosses do not give 9:3:3:1?
Answer: B
Linkage prevents independent assortment, producing more parental types than expected.Q37.
Which is NOT a non-Mendelian pattern?
Answer: D
Simple dominance (Mendelian) is not non-Mendelian—others listed deviate from Mendelian expectations.Q38.
Which is an example where both alleles are fully expressed?
Answer: A
IA and IB are co-dominant—both antigens are expressed in IAIB individuals.Sex Determination & Sex-Linked Traits (Questions 39–46)
Q39.
In humans, males have which sex chromosome combination?
Answer: C
Males are XY; females are XX.Q40.
Which parent determines the sex of the offspring in humans?
Answer: B
Father's sperm provides X or Y, thus determining XX (female) or XY (male).Q41.
Red-green colour blindness is typically inherited as:
Answer: C
Colour blindness is commonly X-linked recessive, more frequent in males.Q42.
A carrier mother (XcX) mating with an unaffected father (XY) will produce sons with what probability of being affected?
Answer: C
Sons have 50% chance of receiving Xc from mother and being affected (XcY).Q43.
Which term describes a sex chromosome complement of XXY in humans?
Answer: B
XXY is Klinefelter syndrome (male with extra X chromosome).Q44.
If father is affected by an X-linked recessive trait, will his sons inherit it?
Answer: B
Sons get Y from father and X from mother; they do not inherit father's X chromosome.Q45.
Which of these is an X-linked dominant trait example (rare)?
Answer: A
Rett syndrome is caused by mutations on X chromosome and exhibits dominant effects (mainly in females).Q46.
Which statement is true about sex chromosomes?
Answer: C
Males produce two types of gametes (X and Y) and are heterogametic; females are homogametic (XX).Human Heredity & Disorders (Questions 47–52)
Q47.
Which blood group genotype corresponds to blood group O?
Answer: C
ii genotype lacks A or B antigens and corresponds to blood group O.Q48.
Cystic fibrosis is inherited as:
Answer: B
Cystic fibrosis is an autosomal recessive disorder (two mutant alleles required).Q49.
A pedigree chart is used to:
Answer: A
Pedigrees help determine patterns (dominant, recessive, X-linked) in families.Q50.
Which practice helps carriers and families manage inherited disorders?
Answer: A
Genetic counselling provides risk assessment, testing options and guidance for families.Q51.
Down syndrome is caused by:
Answer: B
Down syndrome results from an extra copy (trisomy) of chromosome 21.Q52.
Carrier females for X-linked recessive disorders are usually:
Answer: C
Carrier females often do not show phenotype but can pass the mutant X to offspring.Practical, Diagram & Problem Solving (Questions 53–60)
Q53.
A Punnett square is used to:
Answer: B
Punnett squares arrange parental gametes to visualize offspring genotype combos and ratios.Q54.
While doing a test cross of an unknown dominant plant with rr, you get 50% rr offspring. The unknown parent is:
Answer: B
Presence of recessive phenotype in progeny shows the unknown was heterozygous.Q55.
You performed a monohybrid cross and observed 240 dominant and 80 recessive offspring out of 320. This matches expected 3:1. Which calculation confirms it?
Answer: A
3:1 corresponds to 75% dominant and 25% recessive; counts match these percentages.Q56.
When drawing a Punnett square for sex determination, label which gametes for father and mother?
Answer: A
Mother produces X-bearing eggs (X, X) and father produces X- and Y-bearing sperm (X, Y).Q57.
Best short exam tip for genetic cross answers is to:
Answer: B
Clear steps and labelled working earn marks—show symbols, gametes, square and ratios.Q58.
Which resource is the primary syllabus source for CBSE Class 10 Heredity chapter?
Answer: B
NCERT Class 10 Biology is the primary CBSE source—questions aligned to NCERT are exam-relevant.Q59.
Which of the following should you include when answering a long genetics question?
Answer: A
Complete answers need definitions, labelled diagrams, stepwise working and a clear conclusion.Q60.
Quick practical reason to practise many Punnett squares before boards is to:
Answer: B
Practice builds speed and accuracy, ensuring clear presentation and correct ratios in exams.