1
Why do plants in a sugarcane field look almost alike?
💡 Hint:
Asexual or vegetative reproduction.
Explanation:
In vegetative growth the copy stays nearly the same, so the difference is very small.
Class 10 · Science · Chapter 8 · बिहार बोर्ड (BSEB)CBSE · NCERT 2026-27
Heredity
Heredity
How to use this page:
1. Read — Activity 8.1 free and attached earlobes · 8.2 F2 ratio TT:Tt:tt = 1:2:1, diagram, worked example, board tip
2. Check — each lesson has its own questions; the number follows the lesson
3. Mastery ★ — all of that lesson correct. Redo the wrong ones
4. Look at the Punnett-square figure for Tt × Tt showing the genotype ratio 1:2:1.
In NCERT 2026-27 this is chapter 8 and it is only heredity. In the older 16-chapter Bihar book this is chapter 9 and it also has evolution. The last lesson is evolution, labelled as such. Progress stays in this browser.
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- 1 Variation builds up during reproduction
- 2 Mendel’s monohybrid cross — TT, Tt, tt
- 3 Earlobes — Activity 8.1
- 4 Confirming 1:2:1 — Activity 8.2
- 5 Sex determination — XX and XY, the father decides
- 6 Use does not change the DNA of the next generation
- 7 BSEB extra — evolution (not an NCERT 2026-27 activity)
- Chapter winner — every lesson at mastery ★
🎬 Shorts
This chapter has no Short on the channel yet, so ten empty cards are not shown. The notes, diagrams and checks are complete.
📄 PDF download — notes + answer key
Variation builds up during reproduction
जनन में विविधता जमा होती है · NCERT 8.1 · variation
Similar offspring, still a small differenceNotes
Reproduction makes new individuals. The basic body design stays like the parents, but small differences appear too. Those differences are variations.
Plants in a sugarcane field look almost alike, because sugarcane often grows vegetatively. If one bacterium divides into two, and those two divide into four, the four stay very similar. The difference comes only from a small error in copying DNA.
Animals and humans reproduce sexually, so individuals look clearly different. The next generation receives the older differences and also adds new ones. Variation piles up generation after generation.
Worked exampleExample
Question: In an asexual species, trait A is in only 10 percent of individuals and trait B is in 60 percent. Which trait arose earlier?
Answer: Trait B arose earlier. It had more generations in which to spread, so it reached a larger part of the population. A is newer and is still limited to fewer individuals.
Variation also helps survival
Not every variation is equally useful. In a heat wave, the bacteria that can bear heat survive. The environment picks some forms. Later evolution rests on this selection, but that point is kept for the last lesson, with its own label.
10-second revision
- Asexual reproduction gives little variation, only a small copying error
- Sexual reproduction increases variation and it accumulates
- The trait at 60 percent is taken to have arisen before the one at 10 percent
Board tip · BSEBBoard tip
In an objective item, the trait that arose earlier is the one that has spread further in the population.
Board tip · CBSEBoard tip
CBSE asks about survival. Give the heat-tolerant bacteria in one sentence.
Check your understandingall correct = mastery ★
2
Sexual reproduction creates more variation than asexual reproduction.
Explanation:
True — DNA from two parents comes together, and copying errors are added too.
3
In an asexual population, the trait found in 60 percent of individuals arose ______ than the trait found in 10 percent.
💡 Hint:
The one that has spread more had more time.
Explanation:
The trait that has spread further is taken to have arisen earlier.
4
A population survives a heat wave because —
💡 Hint:
Not every form survives equally.
Explanation:
Individuals with a heat-tolerant variation survive and the population continues.
5
How does variation help a species to survive? Give one example.
Model answer (board format)
All individuals are not alike. In a heat wave the bacteria that can bear heat survive and the others may die. Variation therefore saves the population from being wiped out by one shock.
Check your answer:
Mendel’s monohybrid cross — TT, Tt, tt
मेंडल का एक-लक्षण संकरण — TT, Tt, tt · NCERT 8.2.2 · peas · dominant and recessive
Peas gave no middle heightNotes
Mendel chose clear pea traits — tall and short, round and wrinkled seeds, white and violet flowers. He counted the plants in every generation.
Cross a pure tall (TT) with a pure short (tt). In the first generation, F1, there was no middle-height plant. All were tall. The two traits do not melt into a blend.
The tall F1 plants were not pure tall like the tall parent. When they were self-pollinated, about one quarter of the second generation, F2, came out short. Both factors were present in F1, but only tall was shown. A factor is present in two copies. Today we call them genes.
T is dominant, t is recessive
TT is tall. Tt is also tall, because one copy of T is enough. Only tt is short. A trait like T is dominant. A trait like t, which shows only with both copies, is recessive.
F1 plants are all Tt. The Punnett square of F2 is below. The gene combinations are 1 TT : 2 Tt : 1 tt. TT and Tt look equally tall, so the visible ratio becomes 3 tall : 1 short.
Two traits together make new pairsNotes
A cross of tall-round with short-wrinkled gives all tall and round in F1. Tall and round are dominant. F2 has the old pairs and also new ones — tall-wrinkled and short-round. The two traits are inherited independently. The visible ratio is about 9 : 3 : 3 : 1.
Worked exampleExample
Question: A Tt plant is self-pollinated. In 400 seeds, about how many short plants will there be?
Answer: The visible ratio is 3:1, so short plants are about one quarter. One quarter of 400 is 100 short plants. The remaining about 300 are tall, of which about 100 are TT and 200 are Tt.
10-second revision
- No blend in F1 — all tall, genotype Tt
- Dominant T shows with one copy; short needs tt
- F2 phenotype 3:1 and genotype 1:2:1
Board tip · BSEBBoard tip
In BSEB write 3:1 and 1:2:1 together. If you write only 3:1, the mark for the gene combination is lost.
Board tip · CBSEBoard tip
CBSE asks why F1 is not the same as the pure parent. Answer: t is hidden in Tt, and tt brings the short plant back in F2.
Check your understandingall correct = mastery ★
1
What is the F1 of pure tall and pure short peas?
💡 Hint:
There was no middle height.
Explanation:
F1 plants are all Tt and tall. T is dominant.
2
The ratio of gene combinations in the F2 of Tt × Tt is —
💡 Hint:
The Punnett square has one TT, two Tt, one tt.
Explanation:
The genotype is 1 TT : 2 Tt : 1 tt. 3:1 is the visible ratio. 9:3:3:1 is for two traits.
3
A Tt plant is short, because t is present in it.
Explanation:
False — Tt is tall. t is recessive and does not show alone. Only tt is short.
4
A trait that shows even with one copy is called a ______ trait.
💡 Hint:
T is like that.
Explanation:
T is dominant. t is recessive.
5
The F2 ratio when two traits are inherited independently is —
💡 Hint:
New pairs also form, such as tall-wrinkled.
Explanation:
The visible F2 ratio for two traits is 9:3:3:1.
6
How does Mendel’s experiment identify dominant and recessive?
Model answer (board format)
The F1 of TT × tt is all tall, with no middle height. So tall is dominant and short is hidden. Self-pollination of F1 brings the short plant back in F2, about 3:1. The trait that hid in F1 and showed in F2 only with both copies is recessive.
Check your answer:
Earlobes — Activity 8.1
कर्णपालि — क्रियाकलाप 8.1 · NCERT 8.2.1 · Activity 8.1 · Fig. 8.2
One human trait, two formsNotes
The lowest part of the ear is the earlobe. In some students it hangs free of the cheek — a free earlobe. In others it is fixed to the side of the head — an attached earlobe. These are two forms of one trait, not a disease.
A child receives nearly equal genetic material from the mother and the father. So each trait has two copies, one from each parent. Which form shows is tied to Mendel’s rule — the ear does not melt into a middle shape.
Activity 8.1 — the class list and the percentageActivity
Look at the earlobe of every student. Make separate lists for free and attached. Calculate each percentage: (number ÷ total students) × 100.
Then find the type for the parents of each student and match it with the child. Suggest a possible rule from that comparison. The percentage of one class does not become a rule for a whole country. Suggest a rule when many children of the same kind of parents keep showing one form.
Worked exampleExample
Question: In 40 students, 24 have free earlobes. What is the percentage?
Answer: (24 ÷ 40) × 100 = 60 percent free. Attached lobes are 16, that is 40 percent. This is only the count for this class. Without matching the parents it does not become a dominant-recessive rule.
10-second revision
- Free and attached earlobes are two forms of one trait
- Percentage = (number ÷ total) × 100
- Suggest the rule by comparing parents and child, not from one number
Board tip · BSEBBoard tip
The percentage mark comes only when you show the division by the total. Do not write only “more than half”.
Board tip · CBSEBoard tip
CBSE may ask why one class count is not a rule. Answer: the number is small and the parents’ gene combinations can differ.
Check your understandingall correct = mastery ★
1
What is counted in Activity 8.1?
💡 Hint:
The lowest part of the ear.
Explanation:
Activity 8.1 counts the two forms of earlobe and finds the percentage.
2
An attached earlobe is a disease.
Explanation:
False — free and attached earlobes are two ordinary forms in a human population.
3
12 students out of 30 have attached earlobes. The percentage is ______.
💡 Hint:
(12 ÷ 30) × 100.
Explanation:
12/30 = 0.4, so 40 percent.
4
Why does Activity 8.1 ask for the parents’ type?
Model answer (board format)
The class percentage alone does not tell how the trait travelled. Match the child’s form with the mother’s and the father’s, and only then can you suggest a rule of inheritance. A count of one generation is not enough by itself.
Check your answer:
Confirming 1:2:1 — Activity 8.2
1:2:1 की पुष्टि — क्रियाकलाप 8.2 · NCERT Activity 8.2 · Fig. 8.3
3:1 on the outside, 1:2:1 insideNotes
In Fig. 8.3 two kinds of genes are hidden among the tall F2 plants. Both TT and Tt look tall. Only tt looks short. So 1:2:1 cannot be counted by looking at the plants standing in the field.
To confirm it, the progeny of each F2 plant has to be seen. That is the question of Activity 8.2.
Activity 8.2 — self-pollinate the F2Activity
Self-pollinate each F2 plant separately and record its progeny.
- A tall plant that gives only tall offspring is TT.
- A tall plant that gives both tall and short, about 3:1, is Tt.
- A short plant that gives only short offspring is tt.
The count of such plants comes to 1 TT : 2 Tt : 1 tt. The visible 3:1 had been hiding a 1:2:1 of gene combinations.
Worked exampleExample
Question: One tall F2 plant gives only tall progeny. Another tall plant gives 3 tall : 1 short. Write the genes.
Answer: The first is TT, because no hidden t is present. The second is Tt, because the short tt has come back. A short plant itself is tt.
10-second revision
- TT and Tt cannot be separated by looks alone
- The progeny of self-pollination tells whether the plant is pure or Tt
- The confirmed result is 1:2:1
Board tip · BSEBBoard tip
Write three lines: TT only tall, Tt mixed, tt only short. That is the whole activity.
Board tip · CBSEBoard tip
CBSE asks “which experiment?”. The answer must contain self-pollination. Only “cross again” is incomplete.
Check your understandingall correct = mastery ★
1
What is done to confirm 1:2:1 in F2?
💡 Hint:
Activity 8.2.
Explanation:
The progeny of each F2 plant tells whether it is TT, Tt or tt.
2
A tall F2 plant that gives only tall offspring is TT.
Explanation:
True — it has no hidden t. If it were Tt, some short plants would appear.
3
A tall plant gives 72 tall and 24 short offspring. Its gene combination is —
💡 Hint:
72:24 = 3:1.
Explanation:
A 3:1 comes from the plant that is Tt. TT gives only tall plants.
4
A short F2 plant, on self-pollination, gives only ______ offspring.
💡 Hint:
It is tt.
Explanation:
The progeny of tt is tt, so all are short.
5
Why is the 1:2:1 of Fig. 8.3 not visible directly in the field?
Model answer (board format)
Both TT and Tt look tall. The field shows three parts tall and one part short. To separate 1 TT from 2 Tt, each tall plant has to be self-pollinated.
Check your answer:
Sex determination — XX and XY, the father decides
लिंग निर्धारण — XX और XY, पिता तय करता है · NCERT 8.2.4 · Fig. 8.6
In humans, sex is decided by genesNotes
Not every species uses one method. In some reptiles the temperature around the eggs makes a male or a female. Snails can change sex, so there sex is not fixed by genes alone.
In humans sex is mainly genetic. Most chromosomes form 22 pairs, one copy from the mother and one from the father. One pair is different — the sex chromosomes. A woman has both X, that is XX. A man has one ordinary X and one short Y, that is XY.
Half and half, but the father decides
The mother is XX, so every egg carries X. Half the father’s sperms carry X and half carry Y.
If the child receives X from the father, the pair is XX — a daughter. If it receives Y, the pair is XY — a son. So the father decides the sex. The mother gives X in both cases. The chance stays about half and half.
Worked exampleExample
Question: A couple has had three daughters in a row. Must the fourth child be a son, because it is “the son’s turn”?
Answer: No. Each pregnancy is new. The father’s sperm can again be X or Y, with about equal chance. Earlier daughters do not change the next sperm.
10-second revision
- Woman XX, man XY
- The mother always gives X; the father’s X gives a daughter and Y a son
- In some reptiles temperature decides sex; a snail can change sex
Board tip · BSEBBoard tip
The option “the mother decides” is wrong. Write the full sentence: the mother gives X, and the decision is the father’s sperm.
Board tip · CBSEBoard tip
CBSE asks about half and half. Reason: X-bearing and Y-bearing sperms are made equally, and an earlier child does not change the next chance.
Check your understandingall correct = mastery ★
1
In humans a son is formed when —
💡 Hint:
The mother has no Y.
Explanation:
The father’s Y sperm makes a son (XY). An X sperm makes a daughter (XX).
2
In every species the sex of the young is decided only by chromosomes.
Explanation:
False — in some reptiles temperature decides, and some snails change sex.
3
The sex chromosomes of a woman are ______.
💡 Hint:
A man is XY.
Explanation:
A woman is XX and a man is XY.
4
Assertion (A): In humans the father determines the sex of the child.
Reason (R): The mother has no sex chromosome.
Explanation:
A is true. R is false — the mother is XX and gives X in every egg. The decision is whether the father gives X or Y.
5
Instead of a diagram, explain in words why half the children can be sons and half daughters.
Model answer (board format)
The mother is XX, so every child receives X from her. The father is XY, so half his sperms carry X and half carry Y. An X sperm makes an XX daughter and a Y sperm an XY son. The two kinds of sperm are made equally, so the chance is about half and half.
Check your answer:
Use does not change the DNA of the next generation
इस्तेमाल से अगली पीढ़ी का डीएनए नहीं बदलता · NCERT 8.2.3 · genes, proteins and the germ cell
A trait comes from a protein, and the protein from a geneNotes
The DNA of a cell holds the information for making proteins. The stretch of DNA that carries the information for one protein is the gene for that protein.
Take height. If an enzyme works well, more growth hormone is made and the plant is tall. If a change in that gene makes the enzyme weaker, less hormone is made and the plant stays short. A trait changes only when the gene changes.
Both parents put an equal share into the DNA of the offspring, so each gene has two copies. A germ cell takes one copy from each pair. Two germ cells together restore the full pair. Chromosomes are separate pieces, not one unbreakable thread. That is why two traits can stay independent.
Worked exampleExample
Question: A blacksmith swings a hammer every day and the muscles of his arm grow large. Will his child be born with an equally large arm?
Answer: No. Growth of muscle by work is an acquired change of the body. It is not written into the DNA of the germ cell. The child receives the gene for an arm, not the muscle the father built.
The straight argument of the mouse tail
Keep cutting the tails of mice for many generations. The young are still born with tails. Cutting does not change the DNA. Only an altered copy of a gene in the germ cell can change a trait in the next generation.
10-second revision
- A gene is the part of DNA that has the information for one protein
- An acquired muscle or a cut tail does not enter the DNA of the next generation
- A germ cell takes one copy from the pair
Board tip · BSEBBoard tip
Write the definition in two parts: gene = a stretch of DNA, job = the information for one protein.
Board tip · CBSEBoard tip
CBSE asks about equal contribution. Answer: each germ cell carries one set, and together the two sets are complete.
Check your understandingall correct = mastery ★
1
A muscle enlarged by exercise becomes part of the child’s DNA.
Explanation:
False — this is an acquired trait. The DNA of the germ cell does not change because of it.
2
The stretch of DNA that holds the information for one protein is called —
💡 Hint:
The protein carries the effect to the trait.
Explanation:
That stretch is a gene. An enzyme is itself a protein, and it can change height by changing the amount of hormone.
3
A germ cell takes ______ copy of a chromosome from each pair.
💡 Hint:
Two cells together complete the pair.
Explanation:
One copy goes, so that the offspring again has two copies — one from the mother and one from the father.
4
How does a plant become tall or short, if the matter is not exercise?
Model answer (board format)
Height can depend on the efficiency of a protein enzyme that helps make growth hormone. If the gene is unaltered, the enzyme works well, more hormone is made and the plant is tall. If the gene changes and the enzyme is weaker, less hormone is made and the plant stays short. Using the body does not change this DNA.
Check your answer:
BSEB extra — evolution (not an NCERT 2026-27 activity)
BSEB अतिरिक्त — जैव विकास (NCERT 2026-27 का क्रियाकलाप नहीं) · BSEB extra · evolution section of the older book · no NCERT activity
This lesson is not an NCERT 2026-27 activityNotes
Clear label: In NCERT 2026-27, chapter 8 is only heredity. Its activities 8.1 and 8.2 end there. This lesson is not one of those activities.
In the older 16-chapter Bihar book, heredity and evolution were printed together, and that chapter was number 9. The same school-level idea is kept here, separately, for board preparation.
An acquired trait is gained during life — a muscle from exercise, a cut tail, a language that was learned. It does not enter the DNA of the germ cell, so the offspring is not born with it. An inherited trait sits in a gene and travels with reproduction. Evolution runs on these inherited variations, not on the acquired list.
The school-level idea of a new species
If a population is split down the middle — a mountain, a river or a sea comes between — the living things on the two sides can no longer reproduce with each other. Inherited variations collect differently on each side. The form that survives better in that place leaves more offspring.
After many generations the two groups can be so different that they cannot reproduce together. That is speciation at school level — two species from one. It is not a story of one individual changing suddenly.
Worked exampleExample
Question: A beetle population is split in two by a new river. On one side predator birds see the red beetles, while green ones stay hidden in the grass. On the other side there is no such predator. What is possible later?
Answer: On the first side the green colour can increase by inheritance, because more red ones are eaten. On the other side there is no such selection on colour. Over a vast number of generations the two groups can become separate species, if they can no longer reproduce together. A colour painted on a beetle during its life does not pass to the offspring.
10-second revision
- This lesson is not an NCERT 2026-27 activity
- An acquired trait is not passed on; an inherited variation is
- Separate selection in a split population gives the idea of a new species
Board tip · BSEBBoard tip
In the first line of the answer write that the evolution part belongs to the older Bihar book. Then give one example each of acquired and inherited.
Board tip · CBSEBoard tip
In a CBSE-style answer do not write a species as “one individual changing suddenly”. Write: exchange stops and inherited differences collect.
Check your understandingall correct = mastery ★
1
The correct sentence about this extra lesson is —
💡 Hint:
The label is BSEB extra.
Explanation:
The NCERT 2026-27 activities are only 8.1 and 8.2. The evolution lesson is an extra.
2
A language learned during life is written into the child’s DNA.
Explanation:
False — a learned language is acquired. The child learns the language afresh.
3
At school level, the idea of a new species rests on what?
💡 Hint:
Exchange of reproduction has to stop.
Explanation:
Inherited differences collect in a split population. When the groups can no longer reproduce together, the idea of a new species is formed.
4
A trait gained during life and not entered in the DNA is called an ______ trait.
💡 Hint:
Inherited is the opposite.
Explanation:
An acquired trait does not reach the next generation. An inherited trait is in a gene.
5
Write the difference between an acquired and an inherited trait, and say what speciation depends on.
Model answer (board format)
An acquired trait is an event of life, such as a muscle from exercise. It does not enter the DNA of the germ cell, so the offspring does not receive it. An inherited trait is in a gene and travels with reproduction. In the school-level idea of speciation a population splits, inherited variations collect differently on the two sides, and at last the groups cannot reproduce together. This is not an NCERT 2026-27 activity.
Check your answer:
❓ Full question bank — with answers and explanations — 66 questions
Pick a type. The 34 lesson checks are separate — each lesson has as many as its topic needs. All correct earns mastery ★.
BSEB modelpractice · not annual60 tried · 0 correctMultiple choiceMCQ140 tried · 0 correctTrue / falseTrue / false80 tried · 0 correctFill in the blanksFill80 tried · 0 correctMatchMatch20 tried · 0 correctAssertion–reasonAssertion–reason40 tried · 0 correctBalancingBalancing40 tried · 0 correctIdentifyIdentify20 tried · 0 correctShort and longVSA, SA, LA120 tried · 0 correctCBSE-stylenot a PYQ60 tried · 0 correct
No question is marked as a verified past paper. The BSEB set is a model for practice. CBSE items are CBSE-style, not a copy of any year’s paper.
Multiple choice
0/14Pick one option. A wrong try brings a hint.
1
In an asexual species, the trait with the higher percentage usually —
💡 Hint:
It had more time to spread.
Explanation:
The trait at 60 percent is taken to have arisen before the one at 10 percent.
2
The gene combination of the F1 of TT × tt is —
💡 Hint:
All the plants look tall.
Explanation:
F1 is all Tt. Because T is dominant, all are tall.
3
The visible ratio in the F2 of a monohybrid cross is —
💡 Hint:
Both TT and Tt are tall.
Explanation:
Visibly 3 tall : 1 short. The gene combination is separately 1:2:1.
4
In the Punnett square of Tt × Tt the number of tt is —
💡 Hint:
The amber cell in the figure.
Explanation:
One offspring in four is tt. Two are Tt and one is TT.
5
In a cross of tall violet with short white, all progeny are violet but about half are short. The tall parent can be —
💡 Hint:
Half short progeny means T is heterozygous. All violet means the flower is pure dominant.
Explanation:
The tall parent is TtWW. Half the progeny are short because of Tt, and all are violet because of WW.
6
The correct way to get the percentage in Activity 8.1 is —
💡 Hint:
The total number of students goes in the denominator.
Explanation:
The percentage is (number of that form ÷ class total) × 100.
7
If a tall F2 plant gives some short offspring, that plant is —
💡 Hint:
A pure tall plant will not give a short one.
Explanation:
A short offspring comes only when the parent is Tt and tt can be formed.
8
The sex chromosomes of a human girl are —
💡 Hint:
Y goes from the father to a son.
Explanation:
A girl is XX. XY is a son.
9
From whom does a child always receive an X chromosome?
💡 Hint:
The mother is XX.
Explanation:
Every egg carries X, so every child receives X from the mother.
10
The part of DNA that holds the information for one protein is called —
💡 Hint:
An enzyme is made from that information.
Explanation:
That stretch is called a gene.
11
The correct statement about the blacksmith’s large arm is —
💡 Hint:
Exercise does not change the germ cell.
Explanation:
A muscle that was built is an acquired trait. It is not written into the DNA of the next generation.
12
The visible F2 ratio of two traits is usually —
💡 Hint:
New pairs are also formed.
Explanation:
With independent inheritance the F2 is about 9:3:3:1.
13
If children with light eyes usually have parents with light eyes, then —
💡 Hint:
One correlation can fit both ways.
Explanation:
Parents and child showing one form still does not, by itself, prove dominant or recessive.
14
At school level, speciation begins when —
💡 Hint:
This is the BSEB extra idea.
Explanation:
After the split, exchange of reproduction stops and inherited differences collect.
True or false
0/81
The tall F1 peas are actually medium.
Explanation:
False — Mendel found no middle height. All were tall.
2
A tt pea plant is short.
Explanation:
True — shortness needs both copies of t.
3
In Activity 8.2, TT and Tt separate just by looking, without any progeny.
Explanation:
False — both look tall. The difference comes from the progeny of self-pollination.
4
In humans the mother decides the sex of the child because she is XY.
Explanation:
False — the mother is XX. Sex is decided by the father’s X or Y sperm.
5
Every human child receives one X from the mother.
Explanation:
True — the egg carries X.
6
Cutting tails for generations gives the mouse offspring a tailless gene.
Explanation:
False — cutting does not change the DNA. The offspring is born with a tail.
7
A germ cell receives one copy of each chromosome pair.
Explanation:
True — two germ cells together restore two copies.
8
The last lesson on evolution is NCERT 2026-27 Activity 8.3.
Explanation:
False — it is a BSEB extra. The NCERT 2026-27 activities are only 8.1 and 8.2.
Fill in the blanks
0/81
The gene combination of a recessive short plant is ______.
💡 Hint:
A short plant is tt.
Explanation:
One t is not enough.
2
The F2 gene ratio is 1 TT : 2 Tt : ______.
💡 Hint:
The ratio is 1:2:1, and the last term is 1 tt.
Explanation:
The fourth cell of the Punnett square.
3
The sex chromosomes of a man are ______.
💡 Hint:
A man is XY.
Explanation:
One large X and one short Y.
4
The father’s ______ chromosome makes a son.
💡 Hint:
A Y sperm makes an XY son.
Explanation:
An X gives a daughter.
5
The DNA stretch with the information for a protein is called a ______.
💡 Hint:
It is called a gene.
Explanation:
An enzyme is made from it.
6
A trait gained in life, and absent from the DNA, is called ______.
💡 Hint:
Such a trait is called acquired.
Explanation:
The muscle from exercise.
7
The F2 ratio of two independent traits is ______.
💡 Hint:
The ratio is 9:3:3:1.
Explanation:
New pairs are also formed.
8
To find the earlobe percentage, the number is divided by the ______.
💡 Hint:
Divide by the total number of students, then multiply by 100.
Explanation:
Then multiply by 100.
Match
0/21
Match the gene combination with its form.
Column B: A. Pure tall · B. Tall, hidden short · C. Short · D. Son
1. TT
2. Tt
3. tt
4. XY
Explanation:
TT is pure tall, Tt is tall but heterozygous, tt is short, XY is a son.
2
Match the word with its meaning.
Column B: A. Shows with one copy · B. Carries one copy of the pair · C. Gained in life, not in DNA · D. The idea of a new species from a split population
1. Dominant
2. Germ cell
3. Acquired
4. Speciation
Explanation:
Dominant shows with one copy. A germ cell carries one copy. Acquired does not enter the DNA. Speciation is the split-population idea and is not an NCERT activity.
Assertion–reason
0/4Check both statements, then see whether the reason explains the assertion.
1
Assertion (A): Short plants appear in F2 even after F1 was all tall.
Reason (R): In the Tt of F1, t stays hidden and shows again in tt.
Explanation:
Both are true and R is the correct explanation of A.
2
Assertion (A): In humans the sex is decided by the father’s sperm.
Reason (R): The mother is YY and gives only Y.
Explanation:
A is true. R is false — the mother is XX and gives X.
3
Assertion (A): A wrestler’s child is born with a wrestler’s muscle.
Reason (R): An acquired trait is not written into the DNA of the germ cell.
Explanation:
A is false. R is true — the muscle from exercise does not pass to the next generation.
4
Assertion (A): New pairs can form in the F2 of two traits.
Reason (R): The visible ratio of a monohybrid cross is 3:1.
Explanation:
Both are true, but R does not explain A. New pairs form because chromosomes are separate pieces.
Balance the equation
0/4This chapter has no chemical equation. The tray below is only coefficient practice, not a result of this chapter.
1
This is coefficient practice 1, not a result of this chapter. Heredity has no chemical equation.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for making water. Do not treat it as a heredity fact.
2
This is coefficient practice 2, not a result of this chapter. Heredity has no chemical equation.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for making water. Do not treat it as a heredity fact.
3
This is coefficient practice 3, not a result of this chapter. Heredity has no chemical equation.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for making water. Do not treat it as a heredity fact.
4
This is coefficient practice 4, not a result of this chapter. Heredity has no chemical equation.
H2 + O2 → H2O
Explanation: 2H2 + O2 → 2H2O — coefficient practice for making water. Do not treat it as a heredity fact.
Classify
0/21
Place each name as pure dominant, heterozygous, or pure recessive.
TT
Tt
tt
Explanation:
TT is pure dominant tall, Tt is heterozygous tall, tt is pure recessive short.
2
Place each item as inherited, acquired, or the extra evolution idea.
Tall plant from Tt
The blacksmith’s muscle
A population split by a river
Explanation:
Tt is inherited. The muscle is acquired. A split population is the school-level species idea and is not an NCERT activity.
Very short answer
0/51
Write a one-line definition of a dominant trait.
Model answer (board format)
A trait that shows even with one copy of the gene is dominant.
Check your answer:
2
Write the sex chromosomes of a woman and a man.
Model answer (board format)
Woman XX. Man XY.
Check your answer:
3
What is a gene?
Model answer (board format)
A gene is the stretch of DNA that has the information for making one protein.
Check your answer:
4
Write the formula for the percentage in Activity 8.1.
Model answer (board format)
Percentage = (number of students with that earlobe ÷ total students) × 100.
Check your answer:
5
Give one example of an acquired trait.
Model answer (board format)
A muscle enlarged by daily exercise is acquired. It does not enter the child’s DNA.
Check your answer:
Short answer
0/41
How does Mendel’s monohybrid experiment give 3:1?
Model answer (board format)
The F1 of TT × tt is all Tt and tall. The F2 of Tt × Tt makes TT, Tt, Tt and tt. Three of them have T so they are tall, and only tt is short. The visible ratio is 3:1 and the gene combination is 1:2:1.
Check your answer:
2
Write the experiment of Activity 8.2 in your own words.
Model answer (board format)
Each F2 plant is self-pollinated. A tall plant that gives only tall offspring is TT. One that gives both tall and short is Tt. One that gives only short is tt. The count comes to 1:2:1.
Check your answer:
3
How is the sex of a child determined in humans?
Model answer (board format)
The mother is XX and every egg gives X. The father is XY. An X sperm makes an XX daughter and a Y sperm an XY son. So the decision comes from the father.
Check your answer:
4
A man of blood group A and a woman of blood group O have a daughter of group O. Can we say from this alone which of A or O is dominant?
Model answer (board format)
No. This information is not enough. The blood groups of all the progeny are not known. A person of group A can be AA or AO. One daughter does not settle dominant and recessive.
Check your answer:
Long answer
0/31
From Mendel’s experiments, show that traits can be dominant or recessive, and also independent.
Model answer (board format)
The F1 of pure tall and pure short is all tall, so tall is dominant and short is recessive. In F2 the short plant returns as 3:1, and the genes are 1:2:1. In a cross of two traits, F1 is all tall-round, but F2 also forms new pairs such as tall-wrinkled and short-round. The ratio is about 9:3:3:1. So the two traits are inherited independently.
Check your answer:
2
How does the genetic contribution of the mother and the father stay equal? Add the rule of sex as well.
Model answer (board format)
The body cell has chromosomes in pairs. A germ cell takes one copy from each pair. Two germ cells together bring two full sets back to the offspring, one from the mother and one from the father. A woman is XX and a man is XY. The mother always gives X. If the father gives X the child is a daughter, and if he gives Y the child is a son. In the remaining 22 pairs the contribution stays equal.
Check your answer:
3
Write the difference between acquired and inherited. Also write why the last lesson is evolution.
Model answer (board format)
An inherited trait is in a gene and travels with the germ cell, such as TT or tt in peas. An acquired trait is an event of life, such as a muscle from exercise or a cut tail, and it does not change the DNA of the next generation. NCERT 2026-27 chapter 8 is only heredity. The older Bihar book had evolution with this topic. The last lesson is for that, with a clear BSEB extra label, and it is not an NCERT 2026-27 activity.
Check your answer:
BSEB model paper · practice
0/6This model set is for practice. It is not an annual paper of any year.
1
Mendel kept a count of the peas because —
💡 Hint:
Without the count, 3:1 does not appear.
Explanation:
The count itself gave dominant, recessive and the ratio.
2
The recessive combination among these is —
💡 Hint:
Both small copies.
Explanation:
tt is short and recessive.
3
The visible tall : short ratio in F2 is ______.
💡 Hint:
The visible ratio is 3:1.
Explanation:
The gene ratio is different.
4
What is common to free and attached earlobes?
Model answer (board format)
Both are forms of one human trait. Activity 8.1 counts them, finds the percentage and matches them with the parents.
Check your answer:
5
In a few lines, say how variation increases survival.
Model answer (board format)
All individuals of a population are not alike. If the surroundings change, as in a heat wave, some variations survive. So the whole species does not vanish together.
Check your answer:
6
Explain Tt × Tt with the help of a Punnett square. Write both 3:1 and 1:2:1.
Model answer (board format)
The gametes of both parents are T and t. The four pairs are TT, Tt, Tt and tt. The gene combination is 1:2:1. TT and both Tt are tall, and only tt is short, so the visible ratio is 3:1. Activity 8.2 identifies TT and Tt separately by self-pollination.
Check your answer:
CBSE-style questions
0/6These are competency-based practice questions. This is not a past paper.
1
A student counted 15 tall and 5 short among 20 peas. This ratio is close to which?
💡 Hint:
15:5 = 3:1.
Explanation:
This is the visible 3:1. The inner 1:2:1 does not show without the next progeny.
2
A fifth child arrives after four daughters. The most reasonable statement about sex is —
💡 Hint:
An earlier child does not change the next sperm.
Explanation:
In every pregnancy the chance of X and Y is about equal again.
3
Assertion (A): A germ cell has one set of genes.
Reason (R): Two sets together bring the chromosome number back in the offspring.
Explanation:
Both are true and R is linked as the correct reason.
4
Assertion (A): Cutting mouse tails for many generations erases the tail gene.
Reason (R): An acquired change does not enter the DNA of the germ cell.
Explanation:
A is false. R is true. The offspring continues to be born with a tail.
5
10 students out of 25 in a class have attached earlobes. Find the percentage and say why this count does not become a dominant-recessive rule.
Model answer (board format)
(10 ÷ 25) × 100 = 40 percent attached earlobes. The count of one class is small and the parents’ gene combinations can differ. For a rule the children have to be matched with the parents, as Activity 8.1 says.
Check your answer:
6
There are two brothers. The elder has broad shoulders from exercise. The younger did not exercise. Will the elder pass a gene for broad shoulders to his child? Give a reason.
Model answer (board format)
No. Broad shoulders are an acquired result of exercise. The DNA of the germ cell does not change because of it. The child receives the father’s genes, not the muscle that was built. This is the NCERT rule of inheritance; the extra evolution lesson rests on the same point.
Check your answer:
🏛️ Board exam corner — Bihar Board (BSEB)— CBSE
Switch board with BSEB | CBSE above. The lessons follow the same NCERT chapter.
BSEB model · practiceBoard tip
This page has no verified annual-exam question, because no source page has been added. The model set below is practice in the board pattern.
🏛️ Model questions on one page →
The verified label will be used only when a source page for the question is available.
CBSE-style · competency-based
These are case and assertion-reason practice items. Do not treat them as past CBSE questions.
🔁 Spaced review — today’s questions
Wrong questions return soon; correct ones return after a few days.
🧠 What you learned + equation sheet
What you learned
- Sexual reproduction makes more variation; in asexual reproduction only small errors of DNA copying make a difference.
- The F1 of TT × tt is all Tt and all tall. T is dominant and t is recessive.
- In the F2 of Tt × Tt the visible ratio is 3 tall : 1 short, and the gene combinations are 1 TT : 2 Tt : 1 tt.
- Activity 8.1 counts earlobes. Activity 8.2 self-pollinates the F2 plants to check 1:2:1.
- In humans the sex depends on the father’s sperm: X gives a daughter, Y a son. The mother always gives X.
- Using a body part does not change the DNA of the next generation. An acquired trait is not inherited.
| What | Keep this |
|---|---|
| F2 phenotype | 3 tall : 1 short |
| F2 genotype | 1 TT : 2 Tt : 1 tt |
| Dominant / recessive | one T makes tall; short needs tt |
| Sex chromosomes | XX girl, XY boy |
| Germ cell | one copy from each pair |
| Acquired trait | not passed in the DNA |
The notes are original writing. The textbook was used only for activity order and numbers. “Verified” will be used only on a question that has a source page.