CBSE Class 10 Science: Heredity and Evolution — Important Questions with Answers 2026

Short Answer Questions (2-3 Marks)

• Q: What is heredity? Explain Mendel's monohybrid cross with pea plants.
  Ans: Heredity is the transmission of characters/traits from parents to offspring. Mendel's monohybrid cross: Crossed tall (TT) × dwarf (tt) pea plants. F1: All Tt (tall) — tall is dominant. F1 × F1 (Tt × Tt): F2 genotypic ratio — 1 TT : 2 Tt : 1 tt. Phenotypic ratio — 3 Tall : 1 Dwarf (3:1 ratio). This proved the Law of Segregation — alleles separate during gamete formation.
• Q: Explain sex determination in humans.
  Ans: Sex is determined by sex chromosomes (23rd pair). Females: XX (homogametic — all eggs carry X). Males: XY (heterogametic — sperm carry either X or Y). If X-bearing sperm fertilises egg → XX → female child. If Y-bearing sperm fertilises egg → XY → male child. Father determines the sex of the child. Probability of male/female = 50% each. SRY gene on Y chromosome triggers male development.
• Q: What are homologous and analogous organs? Give examples.
  Ans: Homologous organs: Same basic structure and origin but different functions. Example: Forelimbs of human (grasping), whale (swimming), bat (flying), horse (running) — all have same bone pattern (humerus, radius, ulna). Show divergent evolution. Analogous organs: Different structure and origin but similar function. Example: Wings of bird (bones with feathers) and wings of insect (membrane). Show convergent evolution.

Long Answer / Application Questions (4-6 Marks)

• Q: What is speciation? List the factors that lead to speciation.
  Ans: Speciation is the formation of new species from existing ones. Factors: (1) Geographic isolation — physical barriers (mountains, rivers) separate populations. (2) Genetic drift — random changes in gene frequency in small populations. (3) Natural selection — different environments select different traits. (4) Mutation — sudden heritable changes introduce new variations. (5) Reproductive isolation — separated populations cannot interbreed even if brought together.

Exam Tips for This Chapter

• Revise all definitions and laws from Heredity and Evolution — they are commonly asked as 1-2 mark questions
• Practice diagrams related to Heredity and Evolution — neat labelled diagrams carry 2-3 marks
• For numericals, always show formula → substitution → answer with correct units
• Previous year analysis shows Heredity and Evolution carries 8-12 marks in the board exam