🧬 CBSE · Class 10 · Science · Chapter 9

Heredity and
Evolution

Complete chapter resources for CBSE Class 10 Science — topic breakdown, key concepts, sample questions, previous year board questions, and instant AI question paper generation.

4Topics
5–7Board marks
8Sample questions
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Key Concepts — Chapter 9
  • Heredity: transmission of traits from parents to offspring via DNA
  • Dominant allele: expressed when present; masks recessive allele
  • Monohybrid ratio: F2 phenotype 3 : 1 (dominant : recessive)
  • Genotype ratio (F2): 1 TT : 2 Tt : 1 tt
  • Speciation: new species via geographic isolation + genetic drift
  • Homologous organs: same structure, different function → common ancestor
Chapter Overview

What this chapter covers

Heredity is the biological process by which traits are passed from parents to offspring through genes carried on chromosomes. Chapter 9 begins with Gregor Mendel's landmark pea-plant experiments, which established the laws of inheritance. By tracking single traits (monohybrid crosses) across generations, Mendel showed that traits are controlled by discrete units (alleles) and that one allele can dominate another — giving the predictable 3:1 phenotype ratio in the F2 generation.

The chapter then examines how variation arises — through sexual reproduction (recombination at meiosis) and mutations — and why variation is the raw material for evolution. Students learn to distinguish inherited traits (encoded in DNA, passed to offspring) from acquired traits (gained during an organism's life, not heritable). The concept of speciation — how new species form through geographic isolation and the build-up of genetic differences over generations — links individual inheritance to large-scale evolutionary change.

Evolution is addressed through fossil evidence, comparative anatomy (homologous and analogous organs), and molecular biology. The chapter connects Darwin's idea of natural selection to Mendel's genetics, showing how beneficial inherited variations accumulate in a population over time. Board questions regularly probe these connections — asking students to compare evidence types, draw Punnett squares, and explain how isolation leads to new species.

Topics

What's inside Chapter 9

As per NCERT Class 10 Science (CBSE syllabus)

Topic 1
Heredity — Accumulation of Variation
How traits are transmitted through DNA. Role of sexual reproduction in generating variation. Difference between inherited and acquired traits. Why only inherited variations matter for evolution.
Topic 2
Mendel's Laws of Inheritance
Mendel's pea-plant experiments. Law of Dominance and Law of Segregation. Monohybrid cross: Punnett square, F1 and F2 ratios. Phenotype (3:1) and genotype (1:2:1) ratios. Dominant vs recessive alleles.
Topic 3
Sex Determination
Chromosomal basis of sex determination in humans: XX (female) and XY (male). Role of the father in determining the sex of a child. Why sex ratio is approximately 50:50.
Topic 4
Evolution — Evidence and Speciation
Speciation through geographic isolation. Fossil evidence. Homologous vs analogous organs as evidence for evolution. Molecular phylogeny. Tracing human evolutionary history. Evolution is not progress — common misconceptions addressed.
Connections

How this chapter fits in

Useful for setting question difficulty and cross-chapter papers.

Builds on
Ch 8 · How do Organisms Reproduce?
Sexual reproduction, DNA copying, meiosis and variation
Ch 5 · Life Processes
Cell structure, nucleus, chromosomes as carriers of genetic information
Chapter 9 Heredity &
Evolution
Leads to
Class 12 · Genetics & Evolution
Dihybrid crosses, linkage, Hardy-Weinberg equilibrium, molecular evolution
Class 12 · Molecular Basis of Inheritance
DNA structure, replication, transcription, translation
Board Blueprint

Marks & question-type breakdown

Typical pattern based on CBSE Class 10 Science board papers from the last five years.

Question type Marks Typical count What's usually tested
MCQ / Objective 1 1–2 Dominance, F2 ratio, sex determination, type of organ (homologous vs analogous)
Very Short Answer 2 1 Define heredity / variation / speciation; state Mendel's law; name the sex chromosomes
Short Answer 3 1 Monohybrid cross with Punnett square, or explain how speciation occurs
Long Answer / Case-Based 4–5 1 Evolution evidence (fossils, homologous organs, molecular phylogeny) or multi-part genetics problem
Total (approximate) 5–7 4–5 Weightage varies across paper sets and years
Sample Questions

8 sample questions — generated by MarksZen AI

Aligned to CBSE Class 10 Science Chapter 9. Covers all question types across Easy, Medium, and Hard difficulty.

Q1 Easy 1 mark MCQ
In a monohybrid cross between a pure tall (TT) plant and a pure dwarf (tt) plant, the phenotype ratio in the F2 generation is: (a) 1 : 1 (b) 1 : 2 : 1 (c) 3 : 1 (d) 2 : 1
Q2 Easy 2 marks Short Answer
Distinguish between inherited traits and acquired traits. Give one example of each.
Q3 Medium 2 marks Short Answer
A man with blood group A marries a woman with blood group B. Their child has blood group O. Using a Punnett square, show the possible genotypes of the parents and explain how this is possible.
Q4 Medium 3 marks Short Answer
In pea plants, round seeds (R) are dominant over wrinkled seeds (r). A plant heterozygous for seed shape is self-pollinated. (i) Write the cross using standard notation. (ii) Draw the Punnett square for the F1 generation. (iii) State the phenotype ratio and genotype ratio of the offspring.
Q5 Medium 3 marks Short Answer
Explain how sex is determined in human beings. Why is the father responsible for the sex of the child and not the mother?
Q6 Hard 4 marks Short Answer
What is speciation? Explain with the help of an example how geographic isolation can lead to the formation of a new species. What role does natural selection play in this process?
Q7 Hard 4 marks Short Answer
Differentiate between homologous and analogous organs. Give two examples of each and explain what type of evolution each represents. Why are homologous organs considered stronger evidence for common ancestry?
Q8 Hard 5 marks Case-Based
In Mendel's experiment, he crossed a pure-breeding tall pea plant with a pure-breeding dwarf pea plant. All F1 plants were tall. When F1 plants were self-pollinated, he obtained both tall and dwarf plants in the F2 generation. (i) What were the parental genotypes? (ii) What is the genotype of the F1 plants? Why are all F1 plants tall? (iii) Draw a Punnett square for the F1 × F1 cross and state the F2 genotype ratio. (iv) What conclusion did Mendel draw from the reappearance of dwarf plants in F2?
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Previous Year Questions

From CBSE board examinations

Actual questions from past Class 10 Science board papers — Heredity and Evolution chapter.

Board 20223 marks
A cross was made between two pea plants — one with round yellow seeds (RRYY) and another with wrinkled green seeds (rryy). State the phenotype and genotype of (i) F1 plants and (ii) F2 plants. Write the ratio of phenotypes obtained in F2. (All India 2022)
Board 20232 marks
What are fossils? How do they provide evidence for evolution? Give one example of a fossil that serves as a connecting link between two groups of organisms. (Delhi 2023)
Board 20203 marks
(a) Explain the term 'speciation'. List any two factors that could lead to speciation. (b) Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Give reasons for your answer. (CBSE 2020)
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FAQ

Questions teachers ask

How many marks does Heredity and Evolution carry in the CBSE Class 10 board exam? +
Typically 5–7 marks across 3–4 questions — one 1-mark MCQ on Mendel's laws or dominance, one 2-mark short answer on inheritance patterns, and one 3–5 mark question on evolution evidence or speciation. The exact weightage varies by year and set, but this chapter is among the most consistently tested in Class 10 Science.
What is the difference between inherited and acquired traits? Why does it matter for evolution? +
Inherited traits are encoded in DNA and passed from parent to offspring — for example, eye colour, blood group, or seed shape. Acquired traits develop during an organism's lifetime due to environment or experience — for example, a bodybuilder's muscle mass — and are NOT passed to offspring because they do not alter the germ-line DNA. Only inherited (genetic) variations can accumulate across generations and drive evolution.
What is Mendel's Law of Dominance and how is it tested in board exams? +
Mendel's Law of Dominance states that when two contrasting alleles for a trait are present in an organism, only one (the dominant allele) is expressed in the phenotype while the other (recessive) is masked. In CBSE board exams, this is tested through monohybrid cross Punnett squares — students are given parental genotypes and asked to predict the F1 or F2 ratio of phenotypes and genotypes. These are typically 2–3 mark questions.
What are homologous and analogous organs? How do they serve as evidence for evolution? +
Homologous organs have the same fundamental structure (same origin) but perform different functions in different species — for example, the forelimbs of a frog, lizard, bird, and human. They suggest divergent evolution from a common ancestor. Analogous organs perform similar functions but have different structural origins — for example, the wings of a butterfly and a bird. Homologous organs are the stronger evidence for common descent; analogous organs show convergent evolution driven by similar environmental pressures.
How do I generate a custom question paper for Heredity and Evolution using MarksZen? +
Sign up for a free MarksZen account, choose CBSE Class 10 Science, select Chapter 9 (Heredity and Evolution), set your preferred question-type mix (MCQ, short answer, diagram-based) and total marks — the AI generates a complete board-aligned paper with answer key in under 2 minutes, ready for PDF export.