Class 10 Science · Original EZT practice
Heredity (Class 10 Chapter 8): summary and practice
Why do children look like their parents, but not exactly? This chapter opens with how variation accumulates in reproduction, then turns to Mendel's pea plants: how traits pass down, why the F1 all look tall, and why the short trait returns in the F2. All questions are original EZT tutor practice following the chapter's own section order.
8 original worked examples, 8 fresh self-check questions and 4 mixed questions, with explained answers. These are not copied textbook exercises, an official chapter index or a full answer key. No affiliation with NCERT is claimed.
Official sources for topic and edition context, checked 20 October 2026:
1. Accumulation of variation during reproduction
Reproduction produces individuals that are similar but subtly different. Asexual reproduction creates small variation; sexual reproduction creates much more by combining traits from two parents.
2. Mendel's rules of inheritance
Mendel crossed tall and short pea plants. The F1 were all tall; the F2 showed one quarter short - the recessive trait was hidden in the F1, not lost.
3. How traits get expressed
Each trait is carried by a pair of factors, one from each parent. TT and Tt plants are tall because tall is dominant; only tt is short.
4. Sex determination
In humans the mother always contributes an X; the father contributes X or Y. An XX child is a girl and an XY child is a boy, so the father's gamete decides the sex.
Choose, solve, check, then try a fresh question.
Before calculating, read the method prompt and name the condition that makes it useful. Write your own attempt. Open the steps only when you need them, and use the check to catch a wrong sign, unit or interpretation. Finish with the fresh question before reading its answer.
Separate heredity from variation
Choose the method: Heredity passes traits down; variation is how offspring differ.
EZT practice question
A sugarcane field shows almost no variation, while a human family shows plenty. What explains the difference?
Show the worked solution
- Sugarcane is propagated vegetatively - one parent, near-identical copies.
- Humans reproduce sexually - two parents, and their combined traits create far more variation.
Answer: Asexual (vegetative) reproduction produces little variation; sexual reproduction produces much more.
Check: This is exactly the opening observation of the chapter.
Watch for this: Do not say asexual reproduction has zero variation; small differences still arise.
Now try it yourself
Which mode of reproduction maximises variation?
Check your answer
Sexual reproduction.
It combines traits from two different parents in every generation.
Trace Mendel's tall-short cross
Choose the method: Follow the trait through the F1 and F2 generations.
EZT practice question
Mendel crossed pure tall and pure short pea plants. What did the F1 and F2 look like?
Show the worked solution
- The F1 were all tall.
- Self-pollinating the F1 gave an F2 with one quarter short plants.
Answer: F1: all tall. F2: three quarters tall, one quarter short.
Check: The short trait reappearing in the F2 proves it was only hidden in the F1, not lost.
Watch for this: Do not call the F1 medium height; they were tall, not intermediate.
Now try it yourself
What fraction of the F2 is short?
Check your answer
One quarter.
The F2 ratio is three tall to one short.
Read TT, Tt and tt
Choose the method: Dominant T shows whenever present; short shows only as tt.
EZT practice question
Which of TT, Tt and tt are tall, and which are short?
Show the worked solution
- T (tall) is dominant over t (short).
- TT and Tt both show tall; only tt shows short.
Answer: TT and Tt are tall; tt is short.
Check: This is why the F1 (all Tt) looked tall even though they carried t.
Watch for this: Do not say Tt is intermediate; a dominant trait masks the recessive one completely here.
Now try it yourself
What does a plant with genotype tt look like?
Check your answer
Short.
With no dominant T, the recessive trait is expressed.
Work the Tt x Tt cross
Choose the method: Fill the four boxes: TT, Tt, Tt, tt.
EZT practice question
Two Tt plants are crossed. Give the genotypes of the offspring and the ratio of tall to short.
Show the worked solution
- The boxes give TT, Tt, Tt and tt.
- TT and both Tt are tall; tt is short.
Answer: TT, Tt, Tt, tt - three tall to one short (75 percent tall, 25 percent short).
Check: This is the F2 from Mendel's cross, and it matches his one quarter short.
Watch for this: Do not say the recessive trait is lost; it reappears whenever two t factors meet.
Now try it yourself
For a 64-plant F2 from Tt x Tt, how many tall and short do you expect?
Check your answer
About 48 tall and 16 short.
The 3:1 ratio is an expectation, not a guarantee, for a finite count.
Work the TT x tt cross
Choose the method: Every box is the same: Tt.
EZT practice question
A pure tall (TT) plant is crossed with a pure short (tt) plant. Describe the offspring.
Show the worked solution
- One parent gives only T; the other gives only t.
- Every offspring is Tt.
Answer: All Tt, and all tall.
Check: This is Mendel's F1 generation - all tall, as observed.
Watch for this: Do not expect any short plants here; there is no tt box in this cross.
Now try it yourself
Cross Tt with TT - what fraction of offspring are tall?
Check your answer
All of them.
The boxes are TT, Tt, TT, Tt - every one carries a dominant T.
Work the Tt x tt cross
Choose the method: Four boxes: Tt, Tt, tt, tt.
EZT practice question
A Tt plant is crossed with a tt plant. What is the ratio of tall to short offspring?
Show the worked solution
- The boxes give Tt, Tt, tt and tt.
- Tt is tall and tt is short.
Answer: Half tall, half short - a one-to-one ratio.
Check: This cross reveals the hidden t in a tall plant: if any short offspring appear, the tall parent was Tt.
Watch for this: Do not quote the 3:1 ratio here; that belongs to Tt x Tt.
Now try it yourself
Cross Rr x Rr (round and wrinkled seeds) - expected ratio?
Check your answer
Three round to one wrinkled.
Same pattern as Tt x Tt: the dominant trait takes three of the four boxes.
Follow a two-trait cross
Choose the method: Each trait is inherited independently of the other.
EZT practice question
Mendel crossed plants differing in seed shape (round or wrinkled) and seed colour (yellow or green). What did the F2 show?
Show the worked solution
- The F1 showed both dominant traits.
- The F2 showed new combinations - like round-green and wrinkled-yellow - alongside the parental types.
Answer: The F2 showed the parental combinations plus new combinations, showing the two traits are inherited independently.
Check: Independent inheritance is exactly what lets new combinations appear.
Watch for this: Do not assume the traits travel as a pair; they assort independently.
Now try it yourself
What does the appearance of round-green seeds in the F2 tell us?
Check your answer
That seed shape and seed colour are inherited independently.
A combination absent in the parents can only appear if the traits sort separately.
Explain sex determination
Choose the method: The mother gives X always; the father gives X or Y.
EZT practice question
In humans, which parent determines the sex of the child, and how?
Show the worked solution
- The mother's egg always carries X.
- The father's sperm carries X or Y.
- XX gives a girl; XY gives a boy.
Answer: The father: his X-bearing sperm gives a girl (XX), his Y-bearing sperm gives a boy (XY).
Check: Half the sperm carry X and half Y, so the two outcomes are equally likely.
Watch for this: Do not blame or credit the mother; her gametes are always X.
Now try it yourself
What is the chromosome pair in a girl?
Check your answer
XX.
One X comes from each parent.
Try a mixed set
Choose a method or explanation before opening each answer.
1. Dominant versus recessive?
Show answer and reason
A dominant trait shows with one copy; a recessive trait shows only with two copies.
That is why Tt is tall but tt is short.
2. What are F1 and F2?
Show answer and reason
F1 is the first generation from the parental cross; F2 comes from self-pollinating the F1.
Mendel's ratios appear across these generations.
3. Why does the F2 show one quarter short plants?
Show answer and reason
Tt x Tt gives TT, Tt, Tt and tt - and only tt is short.
The recessive trait was hidden in the F1, not lost.
4. Who determines the child's sex?
Show answer and reason
The father - through an X-bearing or Y-bearing sperm.
The mother's egg always carries X.
Try it yourself
Work these on paper before checking any notes. Answers are deliberately not shown here.
- Cross Rr x Rr (round dominant over wrinkled). What ratio do you expect?
- Cross Tt x TT. What fraction of the offspring are tall?
- For a 64-plant F2 from Tt x Tt, how many short plants do you expect?
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Questions about this practice page
- What is the difference between dominant and recessive traits?
- A dominant trait is expressed even with one copy (TT or Tt); a recessive trait appears only with two copies (tt).
- What are the F1 and F2 generations?
- The F1 is the first generation from crossing the parents; the F2 comes from self-pollinating the F1.
- Why does the F2 show one quarter short plants?
- Crossing Tt x Tt gives TT, Tt, Tt and tt. Three carry a dominant T and are tall; only tt is short - so one quarter.
- Is a recessive trait lost when it does not show?
- No. It is only hidden; the factor is still passed on and reappears whenever two copies meet, as in the F2.
- Are these the NCERT exercise questions for Heredity (Class 10)?
- No. EZT pages are original practice following the chapter's section order - use them to prepare for the textbook exercises, not as a substitute for your book.