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Class 10 Science: Heredity, 8 practice questions with answers

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These are 8 practice questions on NCERT Class 10 Science Chapter 8, Heredity, each with a short answer and the textbook page it comes from. They cover Mendel's experiment with tall and short pea plants (the first and second generations, dominant and recessive traits, the 3 : 1 and 1 : 2 : 1 ratios), a numerical on 800 plants, and how the sex of a child is decided. Try each one before you read the answer. The same book has a set on hormones too: the Class 10 Control and Coordination questions.

These questions are our own, drafted with AI help. Every number was re-computed by a test script and every statement was checked against the chapter, but no practising teacher has reviewed them yet. If you find a mistake, please tell us.

Mendel's pea plants

Question 1. When Mendel crossed tall pea plants with short ones, what were the first-generation (F1) plants like? (Half tall, half short; all tall; or all short.)

Answer: all tall. There were no halfway characters: all the F1 plants were tall, and none was of medium height. (Page 130.)

Question 2. In Mendel's F2 generation from tall F1 plants, what fraction of the plants were short? (As a fraction.)

Answer: 1/4. The F2 progeny of the F1 tall plants were not all tall: one quarter of them were short. This shows that both the tallness and the shortness traits were inherited in the F1 plants, but only tallness was expressed. (Page 130.)

Question 3. Assertion (A): A pea plant with one 'T' copy and one 't' copy of the gene is tall. Reason (R): Tallness ('T') is a dominant trait. Choose the correct option: both true and R explains A; both true but R does not explain A; A true and R false; or A false and R true.

Answer: A and R are both true, and R explains A. A single copy of 'T' is enough to make the plant tall, while both copies have to be 't' for the plant to be short. Traits like 'T' are called dominant traits, and those like 't' recessive traits. (Page 130.)

Question 4. What are traits like 'T' and 't' called, and which one is expressed in a plant with one copy of each?

Answer: 'T' is a dominant trait and 't' is a recessive trait. In a Tt plant the dominant trait, tallness, is the one expressed. (Page 130.)

Question 5. A pure tall plant (TT) is crossed with a short plant (tt). What are the F1 plants like, and what is the chance that an F1 plant, self-pollinated, gives a short plant in F2?

Answer: All F1 plants are Tt and tall, because T is dominant. When Tt self-pollinates, the F2 plants are TT : Tt : tt in the ratio 1 : 2 : 1, so the chance of a short plant (tt) is 1/4. (Same reasoning as the textbook's two-generation figure, Figure 8.3, page 130; the application to this cross is ours.)

Question 6. Mendel's tall F1 pea plants (Tt) were self-pollinated and gave 800 F2 plants. (a) Which combinations of T and t appear in F2, and in what proportion? (b) About how many F2 plants are tall, and how many short? (c) About how many of the tall plants carry two 'T' copies (TT)?

Answer: (a) TT : Tt : tt = 1 : 2 : 1. (b) Tall (TT or Tt) = 3/4 × 800 = 600; short (tt) = 1/4 × 800 = 200. (c) TT = 1/4 × 800 = 200, so 200 of the 600 tall plants are TT and 400 are Tt. (The 1 : 2 : 1 ratio, Activity 8.2 and Figure 8.3, page 130.)

Sex determination

Question 7. In humans, the sex of a child is decided by the chromosome inherited from which parent? (The mother; neither, the child's food decides it; or the father, an X or a Y.)

Answer: the father, an X or a Y. Women have a perfect pair of sex chromosomes, both X; men have a mismatched pair, one X and a shorter one called Y. Every child gets an X from the mother; the sex of the child depends on whether the paternal chromosome is X (for girls) or Y (for boys). (Section 8.2.4, page 132; summary, page 133.)

Question 8. A couple's children inherit an X chromosome from the mother and either an X or a Y from the father, with equal chance. What is the probability that their next child is a boy? (As a fraction.)

Answer: 1/2. A boy needs the Y from the father, one of two equally likely chromosomes, so the probability is 1/2. Half the children are expected to be boys. (The X and Y rule is on pages 132 and 133; the probability is our step.)

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Sources

All opened and read on 21 October 2026. Page numbers are the printed page numbers of the textbook.

The experiment, the terms and the X and Y rule are from the textbook pages above. The questions, worked answers and checks are our own, and every number was re-computed by script. This guide is general information; follow your teacher and the textbook.