Heredity – Short Answer Type Questions
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Class: CBSE Class 10
Subject: Science — Biology
Chapter: Chapter 8 — Heredity
CBSE Board Examinations
Systematic order:
Syllabus → Learning Objectives → Topic-wise Short Questions (50)
Syllabus → Learning Objectives → Topic-wise Short Questions (50)
These 50 topic-wise short answer type questions and answers are prepared strictly as per the NCERT syllabus for Class 10 Biology — Chapter 8: Heredity. Each answer is concise and exam-focused for effective learning and revision.
Basics of Heredity & Variation
1. What is heredity?
Heredity is the transmission of characteristics from parents to their offspring through genes.
2. Define variation.
Variation refers to differences in traits among individuals of the same species due to genetic and environmental factors.
3. What is a gene?
A gene is a segment of DNA that carries instructions for a specific trait or function.
4. Define allele.
An allele is one of two or more alternative forms of a gene that determine variations of a trait.
5. Differentiate genotype and phenotype.
Genotype is the genetic constitution (allele combination); phenotype is the observable trait produced by the genotype and environment.
6. What are homologous chromosomes?
Homologous chromosomes are paired chromosomes—one from each parent—carrying genes for the same traits at corresponding positions.
7. What is a trait? Give an example.
A trait is a specific characteristic (e.g., seed shape or eye colour). Example: round or wrinkled seeds in pea plants.
8. How does environment influence variation?
Environmental factors like nutrition, temperature, and light can modify the expression of genes and cause non-genetic variation.
Mendel’s Experiments & Key Concepts
9. Who was Gregor Mendel and why is he important?
Gregor Mendel was a scientist who discovered fundamental principles of inheritance using controlled crosses of pea plants and quantitative analysis.
10. Why were pea plants ideal for Mendel’s experiments?
Pea plants had distinct, easily observable traits, short generation time, and could be artificially cross-pollinated, enabling controlled experiments.
11. What is a monohybrid cross?
A monohybrid cross follows inheritance of a single trait between two individuals with different alleles for that trait.
12. What was Mendel’s P, F1 and F2 generation?
P = parental generation; F1 = first filial generation (offspring of P); F2 = second filial generation (offspring of selfed or crossed F1).
13. State Mendel’s law of segregation in one sentence.
Alleles segregate from each other during gamete formation so each gamete receives only one allele of a gene.
14. State Mendel’s law of independent assortment briefly.
Alleles of different genes assort independently of each other during gamete formation, provided genes are on different chromosomes.
15. What phenotypic ratio did Mendel observe in F2 of monohybrid crosses?
He observed a 3 : 1 phenotypic ratio (dominant : recessive) in F2.
16. What does Mendel’s quantitative approach mean?
Mendel counted large numbers of offspring and used numerical ratios to establish predictable inheritance patterns.
17. Give the significance of pure lines in Mendel’s study.
Pure lines (true-breeding) provided consistent parental traits, allowing clean crosses and reliable interpretation of inheritance.
Alleles, Dominance & Simple Crosses
18. What is dominance in genetics?
Dominance occurs when one allele masks the expression of another allele in a heterozygote.
19. Define homozygous and heterozygous.
Homozygous: two identical alleles (AA or aa). Heterozygous: two different alleles (Aa).
20. Explain with a short example what a Punnett square shows.
A Punnett square predicts offspring genotypes by listing parental gametes on axes and combining them in cells (e.g., Aa × Aa → genotypes AA, Aa, aa).
21. What is genotypic ratio and give an example?
Genotypic ratio shows proportions of genotypes among offspring (e.g., monohybrid F2 gives 1 : 2 : 1 for AA : Aa : aa).
22. Why does a heterozygote show the dominant phenotype?
Because the dominant allele produces a functional product that masks the effect of the recessive allele.
23. What is a test cross?
A test cross is mating an individual with unknown genotype to a homozygous recessive to determine the unknown genotype from offspring ratios.
24. Define back cross briefly.
A back cross is crossing progeny back with one of the parents (or genetically similar individual) to study inheritance or recover parental traits.
25. Explain 1 : 2 : 1 ratio in monohybrid F2.
F2 genotypes TT : Tt : tt appear in ratio 1 : 2 : 1 when two heterozygotes (Tt) are crossed and segregate alleles equally.
26. What is hybrid vigour (heterosis)?
Hybrid vigour refers to superior qualities (growth, yield) shown by hybrid offspring compared to parents, often used in plant breeding.
27. Give one exam tip for answering crosses in board exams.
Show parental genotypes, list gametes, draw a clear Punnett square, and state genotypic & phenotypic ratios as the final answer.
Non-Mendelian Inheritance & Examples
28. What is co-dominance? Give an example.
Co-dominance is when both alleles express equally in heterozygote; example: human blood group AB shows both A and B antigens.
29. What is incomplete dominance?
Incomplete dominance produces an intermediate phenotype in heterozygotes (e.g., red × white → pink in flowers).
30. What are multiple alleles? Name an example.
Multiple alleles are more than two allele forms in a population for a gene; example: ABO blood group system has three alleles (IA, IB, i).
31. Why do Mendel’s laws not always apply?
They may not apply when genes are linked, when multiple alleles, incomplete dominance, co-dominance, or polygenic inheritance occur.
32. Briefly explain polygenic inheritance.
Polygenic inheritance involves many genes contributing to a single trait, producing continuous variation (e.g., height, skin colour).
33. Give one real-life example of non-Mendelian inheritance.
ABO blood grouping (co-dominance and multiple alleles) is a real-life non-Mendelian example.
34. How does linkage affect independent assortment?
Linked genes located close together on the same chromosome tend to be inherited together, breaking the independent assortment pattern.
Sex Determination & Sex-Linked Traits
35. How is sex determined in humans?
Sex is determined by sex chromosomes: females XX, males XY. Sperm (X or Y) from father combines with mother’s X to give XX or XY zygote.
36. Why is father called the heterogametic sex?
Because males produce two types of gametes (X-bearing and Y-bearing sperm) while females produce only X-bearing eggs.
37. What is a sex-linked trait?
A sex-linked trait is one determined by a gene located on a sex chromosome, often showing different patterns in males and females.
38. Give one example of a sex-linked trait.
Red-green colour blindness and haemophilia are common examples of X-linked recessive traits in humans.
39. Why are X-linked recessive disorders more common in males?
Males have only one X chromosome, so a single recessive allele on X manifests the disorder, while females need two copies.
40. How would you show sex determination using a Punnett square?
Write mother’s gametes (X, X) on one axis and father’s gametes (X, Y) on the other; fill cells to show XX and XY possibilities (50% each).
41. Mention one practical application of knowing sex determination.
Understanding sex determination aids in genetic counselling, predicting inheritance of sex-linked disorders, and animal breeding programs.
Human Heredity & Disorders
42. What is a genetic disorder?
A genetic disorder is a disease caused by abnormalities in genes or chromosomes that can be inherited.
43. Give a brief example of a single-gene human trait or disorder.
Colour blindness (X-linked recessive) is an example of a single-gene trait affecting vision in humans.
44. How does blood grouping illustrate genetics?
ABO blood groups show multiple alleles (IA, IB, i) and co-dominance (IA and IB express together in AB), illustrating complex inheritance.
45. Why is genetic counselling important?
Genetic counselling helps assess risks of inherited disorders, informs prospective parents, and suggests management or preventive steps.
46. How does heredity contribute to evolution?
Heredity transmits genetic variation; natural selection acts on this variation, enabling populations to adapt and evolve over generations.
Practical Skills, Diagrams & Exam Tips
47. What diagrams should you practice for this chapter?
Practice Punnett squares for monohybrid crosses, sketch of Mendel’s experimental setup flow (P → F1 → F2), and simple sex-chromosome diagrams.
48. How should you structure a long answer about Mendel’s experiment?
Start with objective and materials, describe crosses and results (with numbers/ratios), state conclusions and significance briefly.
49. Give one tip to avoid common mistakes in genetic problems.
Carefully assign symbols for alleles, list parental gametes clearly, and draw the Punnett square neatly to avoid calculation errors.
50. Provide a quick revision strategy for this chapter.
Memorise key definitions, practise 10–15 Punnett squares, rehearse Mendel’s laws with examples, and solve NCERT questions regularly.
Note: Keep answers concise in exams for short-answer questions. When asked to 'explain' or 'describe', expand with steps, diagrams and ratios where relevant. These Q&A are aligned with NCERT Class 10 Biology Chapter 8: Heredity.