60+ Questions & Answers - NCERT PDF Based (Class 10)
Structured as Part A (1 mark, short answers), Part B (4 marks, ~6 lines answers), Part C (8 marks, detailed). 20 per part, based on PDF questions/exercises/content.
Part A: 1 Mark Questions (Short Answers)
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
1 Mark Answer: Trait B.
2. How does the creation of variations in a species promote survival?
1 Mark Answer: Advantages in environment.
3. How do Mendel’s experiments show that traits may be dominant or recessive?
1 Mark Answer: F1 all dominant.
4. How do Mendel’s experiments show that traits are inherited independently?
1 Mark Answer: New combinations F2.
5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
1 Mark Answer: No; needs more.
6. How is the sex of the child determined in human beings?
1 Mark Answer: Paternal X/Y.
7. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
1 Mark Answer: TtWW.
8. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
1 Mark Answer: Cannot say.
9. Outline a project which aims to find the dominant coat colour in dogs.
1 Mark Answer: Cross breeds.
10. How is the equal genetic contribution of male and female parents ensured in the progeny?
1 Mark Answer: One set each.
11. What is heredity?
1 Mark Answer: Trait inheritance.
12. What are dominant traits?
1 Mark Answer: Express if present.
13. What are recessive traits?
1 Mark Answer: Two copies needed.
14. What is a gene?
1 Mark Answer: Protein info unit.
15. What are chromosomes?
1 Mark Answer: DNA threads.
16. How many pairs of chromosomes in humans?
1 Mark Answer: 23.
17. What determines sex in humans?
1 Mark Answer: XY system.
18. What is F1 generation?
1 Mark Answer: First filial.
19. What ratio in monohybrid F2?
1 Mark Answer: 3:1.
20. What ratio in dihybrid F2?
1 Mark Answer: 9:3:3:1.
Part B: 4 Marks Questions (Answers in ~6 Lines)
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
4 Marks Answer: Trait B likely earlier. In asexual, variations arise slowly. Higher frequency means longer time to spread. Trait A recent, less spread. Example bacteria resistance. Survival selects.
2. How does the creation of variations in a species promote survival?
4 Marks Answer: Variations give advantages. Environment selects (heat wave). Some survive, reproduce. Species continues. Uniform population may die. Basis evolution.
3. How do Mendel’s experiments show that traits may be dominant or recessive?
4 Marks Answer: Cross tall/short peas. F1 all tall. F2 3 tall:1 short. Tall dominant. Short recessive, hidden F1. Two factors per trait.
4. How do Mendel’s experiments show that traits are inherited independently?
4 Marks Answer: Dihybrid round/yellow x wrinkled/green. F1 all round/yellow. F2 new combos (round/green). Traits separate. 9:3:3:1 ratio.
5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
4 Marks Answer: Not enough. Daughter O means both parents O allele. Father AO (A dominant). But needs confirmation. Could be other.
6. How is the sex of the child determined in human beings?
4 Marks Answer: 22 pairs + XY. Women XX, men XY. Child X from mother. X from father girl (XX); Y boy (XY). 50% chance.
7. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
4 Marks Answer: TtWW. Violet dominant (W), tall heterozygous (Tt). F1 violet; half short. Matches observation.
8. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
4 Marks Answer: Cannot say. Light from light parents. Could be recessive (both copies). Needs dark parents data.
9. Outline a project which aims to find the dominant coat colour in dogs.
4 Marks Answer: Cross black/white dogs. Observe F1. All black: black dominant. F2 ratios confirm. Ethical breeding.
10. How is the equal genetic contribution of male and female parents ensured in the progeny?
4 Marks Answer: Meiosis halves sets. Gametes one set. Fusion restores two. One from each parent. Chromosomes pair.
11. What is the role of genes in controlling traits?
4 Marks Answer: Genes code proteins. Proteins control (hormones). Example height enzyme. Alteration changes amount.
12. Explain monohybrid cross ratio.
4 Marks Answer: TT x tt: F1 Tt. F2 TT:Tt:tt 1:2:1 genotype. 3:1 phenotype. Dominant expresses.
13. What are sex chromosomes?
4 Marks Answer: Determine sex. X/Y unpaired. Women XX perfect. Men XY mismatched.
14. How do variations arise in asexual reproduction?
4 Marks Answer: DNA copying errors. Minor inaccuracies. Small differences. Not drastic.
15. Why are traits inherited independently?
4 Marks Answer: Genes on chromosomes. Separate in meiosis. Recombine randomly. New combos.
16. What is the significance of chromosomes in inheritance?
4 Marks Answer: Carry genes. Maternal/paternal copies. Meiosis one each. Restore in zygote.
17. Explain Gregor Mendel's contribution.
4 Marks Answer: Pea experiments. Counted traits. Laws: Dominance, segregation, independence.
18. What happens in F1 of contrasting traits cross?
4 Marks Answer: All dominant. No blend. Recessive hidden.
19. How does environment select variations?
4 Marks Answer: Advantages survive. Example heat wave. Basis evolution.
20. What is the basic outcome of reproduction?
4 Marks Answer: Similar design individuals. Heredity rules ensure.
Part C: 8 Marks Questions (Detailed Answers)
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of the same population, which trait is likely to have arisen earlier?
8 Marks Answer: In asexually reproducing species, variations arise from DNA copying errors and spread slowly over generations. A trait with higher frequency like B (60%) has had more time to accumulate and become common in the population. Trait A (10%) is likely more recent, as it hasn't spread as widely yet. For example, in bacteria, a resistance trait that arose earlier would be present in more individuals if it provides survival advantage. Environmental selection favors beneficial variations, but in stable conditions, frequency indicates age. This promotes species survival by maintaining diversity.
2. How does the creation of variations in a species promote survival?
8 Marks Answer: Variations create differences among individuals, providing advantages in changing environments. Depending on variations, some have better survival chances, like heat-resistant bacteria in a heat wave surviving while others die. Environmental factors select these variants, forming the basis for evolutionary processes. In uniform populations, changes can wipe out the species, but variations ensure some survive and reproduce. Asexual reproduction produces minor variations from DNA errors, while sexual maximizes diversity. This leads to increased survival and adaptation over time.
3. How do Mendel’s experiments show that traits may be dominant or recessive?
8 Marks Answer: Mendel crossed pea plants with contrasting traits like tall and short. The F1 progeny were all tall, showing no blending and that tallness was expressed over shortness. In F2 from self-pollination of F1, 3/4 were tall and 1/4 short, indicating shortness was inherited but not expressed in F1. He proposed two factors (genes) per trait; dominant (T) expresses with one copy, recessive (t) needs two. Genotypes: Parental TT x tt, F1 Tt (tall), F2 TT, Tt, tt (3 tall:1 short). This demonstrates dominance and recessiveness.
4. How do Mendel’s experiments show that traits are inherited independently?
8 Marks Answer: In dihybrid cross, Mendel used two traits: round/yellow vs wrinkled/green seeds. F1 all round/yellow (dominant). F2 showed new combinations: round/green and wrinkled/yellow, besides parental types. Ratio 9:3:3:1 indicates traits assort independently during gamete formation. Factors for shape and color separate and recombine freely. If linked, only parental types would appear. This law of independent assortment explains diversity in sexual reproduction and is due to genes on different chromosomes.
5. A man with blood group A marries a woman with blood group O and their daughter has blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?
8 Marks Answer: The information is not enough to determine dominance. Daughter O means she inherited O from both parents. Mother OO (group O). Father must be AO to contribute O, expressing A (if dominant). If O dominant, father OO, but he is A. Standard knowledge: A dominant over O. But based only on this, multiple possibilities; needs more family data or crosses. Illustrates Mendelian inheritance where phenotypes hide genotypes without tests.
6. How is the sex of the child determined in human beings?
8 Marks Answer: Humans have 22 autosome pairs + one sex chromosome pair. Females XX (perfect pair), males XY (mismatched). During meiosis, gametes get one set: Female eggs all X, male sperms half X/half Y. Zygote: XX (girl) if X sperm, XY (boy) if Y sperm. All children inherit X from mother; father determines sex. 50% chance each. Differs from environmental determination in some species like reptiles.
7. A Mendelian experiment consisted of breeding tall pea plants bearing violet flowers with short pea plants bearing white flowers. The progeny all bore violet flowers, but almost half of them were short. This suggests that the genetic make-up of the tall parent can be depicted as
8 Marks Answer: The tall parent is TtWW. Violet (W) dominant over white (w), so F1 violet means tall parent WW or Ww; but all violet suggests WW. Height: Half short means tall parent heterozygous Tt (T dominant). Cross: TtWW x ttww. F1: TtWw (tall violet), ttWw (short violet). Matches observation. Demonstrates independent assortment and dominance.
8. A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis, can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
8 Marks Answer: We cannot determine if light eye color is dominant or recessive from this alone. Light-eyed children from light-eyed parents could mean light is recessive (both parents homozygous recessive, children too). If dominant, possible but doesn't explain why not from dark parents. Needs data on dark-eyed parents producing light-eyed children (recessive) or vice versa. Similar to Mendel's peas where phenotypes need crosses to reveal dominance.
9. Outline a project which aims to find the dominant coat colour in dogs.
8 Marks Answer: Aim: Determine if black or white coat is dominant. Method: Select pure black and pure white dogs (homozygous from pedigree). Cross them (monohybrid). Observe F1: All black means black dominant. Self-cross F1 for F2: 3 black:1 white confirms. Ethical: Use small sample, veterinary care. Record ratios, genotypes. Conclude based on Mendel principles. Extensions: Multiple traits.
10. How is the equal genetic contribution of male and female parents ensured in the progeny?
8 Marks Answer: Cells have two gene sets, one from each parent. Germ-cells form by meiosis, halving to one set. Male and female gametes each contribute one set. Fusion in zygote restores two sets, equal from parents. Chromosomes as independent pieces ensure random maternal/paternal mix. This maintains species DNA stability and explains Mendel results where traits from both appear.
11. Explain how traits get expressed.
8 Marks Answer: Cellular DNA provides protein info; gene for one protein. Proteins control traits, e.g., plant hormone for height. Gene codes enzyme for hormone; efficient enzyme makes tall plant, altered less efficient makes short. Both parents contribute gene copy via gametes. Dominant expresses. Meiosis ensures one set per gamete. Explains inheritance patterns.
12. Describe Mendel's monohybrid experiment.
8 Marks Answer: Mendel crossed pure tall (TT) and short (tt) peas. F1 all tall (Tt), showing dominance. Self-pollinated F1: F2 TT, Tt, Tt, tt - 3 tall:1 short phenotype, 1:2:1 genotype. No blending. Proposed two factors segregate. Counted thousands for ratios. Basis law of dominance/segregation.
13. How do variations accumulate during reproduction?
8 Marks Answer: Inheritance gives basic design + subtle changes. Next generation adds new differences. Asexual: Minor from DNA errors. Sexual: Greater diversity. Single individual reproduction like bacteria: Similar with minor differences. Environment selects for survival. Leads to evolution over generations.
14. Explain independent inheritance with dihybrid example.
8 Marks Answer: Cross RRYY (round yellow) x rryy (wrinkled green). F1 RrYy all round yellow. F2: 9 round yellow, 3 round green, 3 wrinkled yellow, 1 wrinkled green. New combos show shape/color independent. Genes assort separately in gametes. Ratio 9:3:3:1. Mendel calculated percentages.
15. What is the mechanism of heredity?
8 Marks Answer: DNA copies during reproduction. Genes on chromosomes. Two copies per cell, one maternal/paternal. Meiosis: One chromosome per pair to gamete. Fusion: Restores pairs. Ensures equal contribution. Explains Mendel: Traits segregate, assort independently if on different chromosomes.
16. Describe sex determination strategies.
8 Marks Answer: Varies: Environmental (reptiles temperature for male/female), changeable (snails). Humans genetic: XX female, XY male. Some rely on cues, others genes. Humans: Father Y for boy. Not always paired like autosomes. Ensures 50% ratio.
17. How do genes control characteristics?
8 Marks Answer: Genes provide protein info. Example: Height hormone enzyme. Efficient gene: More hormone, tall. Altered: Less, short. Traits from protein function. Both parents contribute. Dominant/recessive determine expression. Links DNA to phenotype.
18. What are inherited traits?
8 Marks Answer: Traits passed from parents, like human features. Child resembles but not exact. Populations show variations. Example earlobes free/attached. Activity: Correlate with parents. Rules: Both contribute equal DNA. Basis heredity study.
19. Explain Mendel's pea experiments setup.
8 Marks Answer: Used contrasting visible: Round/wrinkled, tall/short. Pure lines by self-pollination. Crossed opposites. Counted F1, F2 ratios. Blended science/math. First to quantify inheritance. Laws from data. Peas easy, quick generations.
20. How does sexual reproduction create greater diversity?
8 Marks Answer: Combines variations from two individuals. Meiosis shuffles genes. Gametes unique. Fusion new combos. Asexual minor errors only. Greater diversity aids survival in changes. Mendel showed with independent assortment.
Practice Tip: Time yourself; use ratios for long Q.
