Q1. What is heredity?

Answer: Heredity is the transmission of characters or traits from parents to offspring.

Q2. What is genetics?

Answer: Genetics is the branch of biology that studies heredity and variation.

Q3. What is variation?

Answer: Variation means differences in traits among individuals of the same species.

Q4. What is a gene?

Answer: A gene is a segment of DNA that controls a specific trait.

Q5. What is an allele?

Answer: An allele is an alternative form of a gene that controls the same trait.

Q6. What is genotype?

Answer: Genotype is the genetic constitution of an organism for a particular trait. Example: TT, Tt or tt.

Q7. What is phenotype?

Answer: Phenotype is the visible expression of a trait. Example: tall plant or dwarf plant.

Q8. What is a dominant allele?

Answer: A dominant allele is an allele that expresses itself even in the presence of a recessive allele.

Q9. What is a recessive allele?

Answer: A recessive allele expresses itself only when both alleles are recessive.

Q10. What is a Punnett square?

Answer: A Punnett square is a diagram used to predict the possible genotypes of offspring from a genetic cross.

Q11. What is an inherited trait?

Answer: A trait passed from parents to offspring through genes is called an inherited trait.

Q12. What is an acquired trait?

Answer: A trait developed during the lifetime of an organism due to environment or use and disuse is called an acquired trait.

Q13. Who is known as the father of genetics?

Answer: Gregor Johann Mendel.

Q14. What is the chromosomal combination of a human male?

Answer: XY.

Q15. What is the chromosomal combination of a human female?

Answer: XX.

Q16. What is evolution?

Answer: Evolution is the gradual change in inherited traits of populations over many generations.

Q17. What are fossils?

Answer: Fossils are preserved remains, impressions or traces of ancient organisms.

Q18. What is speciation?

Answer: Speciation is the formation of new species from existing species.

Q19. Which blood group is called universal donor in school-level classification?

Answer: Blood group O negative is commonly called the universal donor.

Q20. Which blood group is called universal recipient in school-level classification?

Answer: Blood group AB positive is commonly called the universal recipient.

Q1. A child resembles both parents but is not exactly identical to either of them. Explain why.

Answer:

• The child receives half of its genetic material from the mother and half from the father.
• During sexual reproduction, genes from both parents combine in new ways.
• This creates variations in the offspring.
• Therefore, the child resembles both parents but is not exactly identical to either parent.

Q2. Why are variations important for the survival of a species?

Answer: Variations are important because:

• They help some individuals survive better in changing environmental conditions.
• They increase adaptability of a population.
• Useful variations may be passed to the next generation.
• They provide raw material for evolution.

Q3. A tall pea plant has genotype TT and another tall pea plant has genotype Tt. Are their phenotypes and genotypes same?

Answer: Their phenotype is same because both plants are tall. Their genotype is different because one is TT and the other is Tt.

Q4. Why is a recessive trait not visible in a heterozygous condition?

Answer: In a heterozygous condition, one dominant allele and one recessive allele are present. The dominant allele expresses itself and masks the effect of the recessive allele. Therefore, the recessive trait is not visible.

Q5. How can a tall pea plant have a dwarf offspring?

Answer: A tall pea plant can have a dwarf offspring if both parents are heterozygous tall, Tt. Each parent can pass the recessive allele t. When offspring receives t from both parents, genotype becomes tt and the plant becomes dwarf.

Q6. Differentiate between genotype and phenotype.

Q7. Differentiate between homozygous and heterozygous condition.

Q8. Why did Mendel select pea plant for his experiments?

Answer: Mendel selected pea plant because:

• Pea plants have many contrasting traits.
• They have a short life cycle.
• They produce many seeds.
• Self-pollination and cross-pollination can be easily controlled.
• Pure breeding varieties were available.

Q9. A student cuts the tail of mice for many generations. Will tailless mice be born? Give reason.

Answer: No. Cutting the tail is an acquired trait. It does not change the genes present in reproductive cells. Therefore, it is not inherited by the next generation.

Q10. How is the sex of a human child determined?

Answer: Human females have XX chromosomes and produce eggs with only X chromosome. Human males have XY chromosomes and produce sperm with either X or Y chromosome. If an X sperm fertilises the egg, the child is female. If a Y sperm fertilises the egg, the child is male.

Q11. Why is the father responsible for determining the sex of a child?

Answer: The mother produces only X-bearing eggs, while the father produces both X-bearing and Y-bearing sperm. Therefore, the type of sperm that fertilises the egg determines whether the child will be male or female.

Q12. Why is blood group AB called codominant?

Answer: In blood group AB, both I^A and I^B alleles express themselves equally. Neither allele masks the other. Therefore, they show codominance.

Q1. Explain Mendel’s monohybrid cross using tall and dwarf pea plants.

Answer: Mendel crossed a pure tall pea plant with a pure dwarf pea plant.

Parental generation:

TT × tt

Gametes:

T and t

F₁ generation:

All Tt plants are tall

This shows that tallness is dominant over dwarfness.

When F₁ plants were self-crossed:

Tt × Tt

F₂ genotypic ratio: 1 TT : 2 Tt : 1 tt

F₂ phenotypic ratio: 3 tall : 1 dwarf

Q2. Explain Mendel’s laws of inheritance with examples.

Answer:

• Law of Dominance: When two contrasting alleles are present together, only one expresses itself. Example: In Tt, tallness appears because T is dominant over t.
• Law of Segregation: The two alleles of a trait separate during gamete formation, so each gamete receives only one allele.
• Law of Independent Assortment: In a dihybrid cross, alleles of different traits are inherited independently of one another, if they are located on different chromosomes.

Q3. Explain Mendel’s dihybrid cross and its conclusion.

Answer: Mendel crossed pea plants having two pairs of contrasting traits: round yellow seeds and wrinkled green seeds.

Parental cross:

RRYY × rryy

F₁ generation:

All RrYy plants with round yellow seeds

When F₁ plants were self-crossed, four types of phenotypes appeared in F₂ generation:

• Round yellow
• Round green
• Wrinkled yellow
• Wrinkled green

F₂ phenotypic ratio:

9 : 3 : 3 : 1

Conclusion: Traits are inherited independently. This supports the law of independent assortment.

Q4. Explain the difference between acquired and inherited traits with examples.

Q5. Explain sex determination in human beings using a Punnett square.

Answer: In humans, females have XX chromosomes and males have XY chromosomes.

• Mother produces eggs carrying X chromosome only.
• Father produces sperm carrying either X or Y chromosome.
• If X sperm fertilises the egg, the child is XX, female.
• If Y sperm fertilises the egg, the child is XY, male.

Result: There is a 50% chance of a male child and 50% chance of a female child.

Q6. Explain ABO blood group inheritance.

Answer: Human ABO blood group is controlled by three alleles: I^A, I^B and i.

• I^A produces A antigen.
• I^B produces B antigen.
• i does not produce A or B antigen.
• I^A and I^B are codominant.
• Both I^A and I^B are dominant over i.

Q7. Explain evolution and how variation contributes to it.

Answer: Evolution is the gradual change in inherited traits of organisms over many generations.

• Variations arise due to sexual reproduction, mutation and errors in DNA copying.
• Some variations help organisms survive better in a particular environment.
• Organisms with useful variations reproduce more successfully.
• These useful traits become more common in the population.
• Over many generations, accumulation of such changes may lead to evolution.

Q8. Explain speciation and factors responsible for it.

Answer: Speciation is the formation of a new species from an existing species.

Factors responsible for speciation:

• Geographical isolation: A population may get separated by mountains, rivers or other barriers.
• Genetic drift: Random changes in gene frequency may occur in small populations.
• Natural selection: Nature selects organisms with useful variations.
• Mutation: Sudden changes in DNA may produce new variations.
• Reproductive isolation: Over time, separated groups may become unable to reproduce with each other.

Q9. Explain homologous and analogous organs with examples.

Q10. How do fossils provide evidence for evolution?

Answer: Fossils provide evidence for evolution because:

• They show the remains or impressions of organisms that lived in the past.
• They help compare ancient organisms with present organisms.
• Older fossils are usually found in deeper rock layers.
• Fossils show gradual changes in organisms over time.
• They help scientists understand evolutionary relationships.

Q1. If both parents are tall, can they have a dwarf child? Explain with genotype.

Answer: Yes. If both parents are heterozygous tall, Tt, they can produce a dwarf child with genotype tt. The cross Tt × Tt gives 25% chance of dwarf offspring.

Q2. Why is variation more common in sexually reproducing organisms than in asexually reproducing organisms?

Answer: Sexual reproduction involves fusion of gametes from two parents. This combines genes in new ways and produces more variation. Asexual reproduction involves only one parent, so variation is comparatively less.

Q3. A person learns swimming and becomes a strong swimmer. Will this skill be inherited by the child?

Answer: No. Swimming skill is an acquired trait. It does not change the DNA of reproductive cells, so it cannot be inherited.

Q4. Why are fossils found in upper layers generally more recent than fossils found in deeper layers?

Answer: Sedimentary rock layers form over time. Older layers are usually deeper, while newer layers are deposited above them. Therefore, fossils in upper layers are generally more recent.

Q5. A bird wing and bat wing are used for flying. Are they necessarily homologous? Explain carefully.

Answer: Bird wing and bat wing perform the same function of flying, but their detailed structure and evolutionary origin differ in many ways. They are often treated as analogous organs for flight. However, their forelimb bones also show common vertebrate ancestry, so students must answer according to the comparison being asked.

Q6. Why does natural selection act on phenotype but evolution depends on inherited genotype?

Answer: Nature selects visible traits that affect survival and reproduction. These visible traits are phenotypes. However, only traits controlled by genes can be passed to the next generation. Therefore, evolution depends on inherited genotypes.

Q7. Can two parents with blood groups A and B have a child with blood group AB?

Answer: Yes. If the child receives I^A allele from the A blood group parent and I^B allele from the B blood group parent, the child will have genotype I^AI^B and blood group AB.

Q8. Why does a small isolated population evolve differently from a large population?

Answer: In a small isolated population, random changes in gene frequency can have a strong effect. This is called genetic drift. Over time, such changes may make the population different from the original population.

Q9. Why is the appearance of a new trait not enough to prove evolution?

Answer: A new trait contributes to evolution only if it is inherited and affects the population over generations. Acquired traits may appear in an individual but do not cause evolution if they are not passed to offspring.

Q10. Why is classification linked with evolution?

Answer: Classification groups organisms based on similarities and differences. Organisms with more similarities are likely to have a more recent common ancestor. Therefore, classification helps in understanding evolutionary relationships.

Q1. How do Mendel’s experiments show that traits may be dominant or recessive?

Answer: Mendel crossed pure tall pea plants with pure dwarf pea plants. All F₁ plants were tall, showing that tallness is dominant. When F₁ plants were self-crossed, dwarf plants reappeared in F₂ generation, showing that dwarfness is recessive and was hidden in F₁.

Q2. A man with blood group A marries a woman with blood group O. Can they have a child with blood group O?

Answer: Yes, if the man has genotype I^Ai and the woman has genotype ii. The child can receive i from both parents and have genotype ii, giving blood group O.

Q3. What is the difference between inherited and acquired characters?

Answer: Inherited characters are controlled by genes and passed from parents to offspring. Acquired characters develop during the lifetime of an organism and are usually not inherited because they do not change DNA of reproductive cells.

Q4. Why are traits acquired during lifetime not inherited?

Answer: Acquired traits affect only body cells and do not cause changes in the DNA of germ cells. Since only germ cell DNA is passed to offspring, acquired traits are not inherited.

Q5. Explain how sex is determined in human beings.

Answer: Females have XX chromosomes and males have XY chromosomes. The egg always carries X chromosome. The sperm may carry X or Y chromosome. X sperm produces a female child, while Y sperm produces a male child. Therefore, the father determines the sex of the child.

Q6. What are homologous organs? Give one example.

Answer: Organs that have the same basic structure but perform different functions are called homologous organs. Example: forelimbs of humans and wings of bats.

Q7. What are analogous organs? Give one example.

Answer: Organs that have different basic structure but perform similar functions are called analogous organs. Example: wings of birds and wings of insects.

Q8. How does geographical isolation lead to speciation?

Answer: Geographical barriers separate populations. Over time, different variations, genetic drift and natural selection act on each population. Gradually, they become so different that they can no longer interbreed, leading to formation of new species.

Q1. In a cross between two heterozygous tall plants, what percentage of offspring will be pure tall?

Answer: Tt × Tt gives TT, Tt, Tt and tt. Pure tall plants have genotype TT. Therefore, 25% offspring will be pure tall.

Q2. In a monohybrid cross, the phenotype ratio is 3:1 but genotype ratio is 1:2:1. Explain why.

Answer: TT and Tt both show tall phenotype because T is dominant. Therefore, three plants appear tall and one appears dwarf. Genetically, they are TT, Tt, Tt and tt, so genotype ratio is 1:2:1.

Q3. A child has blood group AB. Can one parent have blood group O? Explain.

Answer: No. A child with blood group AB must receive I^A allele from one parent and I^B allele from the other. A person with blood group O has genotype ii and cannot provide I^A or I^B.

Q4. A population of beetles has green and red beetles. Birds can see red beetles easily. Which beetles are more likely to survive and why?

Answer: Green beetles are more likely to survive because they are better camouflaged. Natural selection favours the trait that gives survival advantage.

Q5. A mutation occurs in a skin cell. Will it be inherited by the next generation?

Answer: No. A mutation in a skin cell affects only body cells. It will be inherited only if it occurs in germ cells or reproductive cells.

Q6. Why does a recessive allele remain in a population even when it is not visible?

Answer: A recessive allele can remain hidden in heterozygous individuals. These carriers show the dominant phenotype but can pass the recessive allele to offspring.

Q7. If a population gets separated by a river, will speciation happen immediately?

Answer: No. Speciation takes many generations. The separated populations must accumulate genetic differences and become reproductively isolated before they become different species.

Q8. If two organisms look similar externally, are they always closely related?

Answer: Not always. Similar appearance may be due to similar adaptation. To know evolutionary relationship, scientists compare internal structure, DNA, development and fossils.

Q1. Assertion: Variation is important for evolution. Reason: Useful variations may help organisms survive and reproduce.

Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.

Q2. Assertion: A recessive trait may disappear in F₁ generation and reappear in F₂. Reason: Recessive allele is destroyed in F₁ generation.

Answer: C. Assertion is true but Reason is false. The recessive allele is not destroyed; it remains hidden in heterozygous condition.

Q3. Assertion: The father determines the sex of a human child. Reason: The father produces both X-bearing and Y-bearing sperm.

Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.

Q4. Assertion: Acquired traits are usually not inherited. Reason: Acquired traits do not change DNA of germ cells.

Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.

Q5. Assertion: Homologous organs show common ancestry. Reason: They have similar basic structure but may perform different functions.

Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.

Q6. Assertion: Blood group AB shows codominance. Reason: Both I^A and I^B alleles express themselves together.

Answer: A. Both Assertion and Reason are true and Reason is the correct explanation.