Heredity · Class 10 Science: 162 MCQs with answers

Q1. A pea plant showing the recessive trait has a genotype that is:

Q2. Why did Mendel select garden pea plants for his experiments?

Q3. Describe Mendel's monohybrid cross up to the F2 generation.

Q4. Define dominant and recessive traits with the pea-height example.

Q5. Distinguish between genotype and phenotype with examples.

Q6. How does a Punnett square predict the outcome of Tt × Tt?

Q7. The smallest F2 class (1/16) is:

Q8. Describe Mendel's dihybrid cross up to F2 with its ratio.

Q9. List the gametes formed by an RrYy plant and explain the number.

Q10. Why is the progeny's chromosome number the same as the parents'?

Q11. How is it established that both parents contribute equally to the child's inheritance?

Q12. Every egg cell carries the sex chromosome:

Q13. An XY zygote develops into a:

Q14. The child's sex is decided by the gamete of the:

Q15. A daughter's two X chromosomes come from:

Q16. A son's Y chromosome came from his:

Q17. How is the sex of a child determined in human beings?

Q18. Why does the mother's gamete play no role in deciding the child's sex?

Q19. Show the cross between human parents for sex determination and give the ratio.

Q20. Describe sex determination in animals where it is not chromosomal.

Q21. What is special about the human male's sex-chromosome pair?

Q22. What is a Punnett square used for?

Q23. Mendel's 'factors' are known today as:

Q24. A cross in which only ONE pair of contrasting traits is followed is called a:

Q25. TT and Tt plants look identical because:

Q26. The F2 short plants prove that F1 tall plants:

Q27. A Tt × tt cross gives offspring in the ratio:

Q28. A tall plant selfed gives ONLY tall offspring. Its genotype is:

Q29. A tall plant selfed produces some short offspring. It must be:

Q30. What fraction of F2 offspring are Tt?

Q31. What fraction of F2 plants breed true for tallness?

Q32. Mendel kept his starting lines pure by exploiting peas':

Q33. In Mendel's notation the parents, their offspring and the next generation are labelled respectively:

Q34. In pea seed colour, yellow is dominant. A yy plant's seeds are:

Q35. Yy × Yy gives green-seeded offspring with probability:

Q36. What did the reappearance of the short trait in F2 prove?

Q37. State the F2 ratios of a monohybrid cross and explain why they differ.

Q38. How would you determine whether a tall pea plant is TT or Tt?

Q39. Why are Mendel's ratios approximate rather than exact in any single experiment?

Q40. How do Mendel's experiments show that traits may be inherited but not expressed?

Q41. Round-green offspring from round-yellow × wrinkled-green parents prove:

Q42. The genotype of a round-green F2 plant could be:

Q43. A wrinkled-yellow F2 plant's genotype could be:

Q44. In the height-gene story, the tall plant's enzyme:

Q45. The short (tt) plant is short because:

Q46. In Tt, why is the plant NOT semi-tall?

Q47. Mendel's factor pairs correspond physically to:

Q48. Independent assortment happens because:

Q49. What fraction of dihybrid F2 offspring show at least one recessive trait?

Q50. The fraction of F2 that is wrinkled-green (rryy):

Q51. What do the new combinations in the dihybrid F2 prove?

Q52. Show that the monohybrid ratio survives inside the dihybrid F2.

Q53. How do genes control characteristics? Explain with the plant-height example.

Q54. Explain dominance in terms of the protein a gene makes.

Q55. How does the behaviour of chromosomes explain Mendel's rules?

Q56. A round-yellow F2 pea is selfed and some offspring are wrinkled-green. What was the parent's genotype and why?

Q57. A zygote is found to be XX. It will develop into a:

Q58. The Y chromosome functions mainly as:

Q59. Sex determination in humans is called CHROMOSOMAL because:

Q60. Which is an example of NON-genetic sex determination?

Q61. Warm beaches producing mostly female turtle hatchlings illustrates:

Q62. The egg and the sperm each contribute how many chromosomes to a human zygote?

Q63. The X chromosome differs from Y chiefly in:

Q64. A region reporting 850 girls per 1000 boys most likely reflects:

Q65. The arithmetic parallel between Tt × Tt and XX × XY is that both:

Q66. Why do the statistics of a single family not always show the 1:1 ratio?

Q67. Explain why blaming women for the birth of daughters is unscientific and harmful.

Q68. How does sex determination demonstrate Mendel's rules of inheritance?

Q69. Why is a strongly skewed child sex ratio in a region a warning sign?

Q70. Why does climate change threaten species with temperature-dependent sex determination?

Q71. Consider these statements about heredity and variation. I. Heredity is the passing of traits from parents to offspring. II. It is why children resemble their parents. III. Variation arises from copying errors and from the mixing of two parents' DNA. IV. Reproduction produces similarity only, never difference. Which statements are correct?

Q72. Which feature of the garden pea was essential to Mendel's method and could not have been replaced?

Q73. Which statement best explains why Mendel succeeded where earlier plant breeders had not?

Q74. Assertion (A): Mendel's ratios only became clear because he counted hundreds of offspring rather than a handful. Reason (R): Inheritance works by chance at each fertilisation, so the expected proportions emerge only over large numbers.

Q75. A pure tall pea plant is crossed with a pure short one and every plant of the next generation is tall. What does this show?

Q76. Which statement correctly defines a DOMINANT and a RECESSIVE trait?

Q77. Which statement best explains why the reappearance of short plants in the F2 generation was the decisive result of Mendel's monohybrid cross?

Q78. Which statement correctly distinguishes an organism's GENOTYPE from its PHENOTYPE?

Q79. Why must a short pea plant always be tt, while a tall one may be either TT or Tt?

Q80. Consider these statements about factors, now called genes. I. Each trait is controlled by a pair of factors. II. One factor of the pair comes from each parent. III. Each gamete carries only one factor of the pair. IV. The two factors of a pair blend together in the offspring. Which statements are correct?

Q81. Which statement best explains why each gamete must carry only ONE factor of a trait pair?

Q82. Which statement best explains why the same rules of inheritance were found to govern peas, fruit flies and human beings alike?

Q83. Which statement best explains why Mendel could be sure his starting plants were pure-breeding before any cross was made?

Q84. In pea seeds, yellow is dominant over green. Two yellow-seeded plants are crossed and about a quarter of their offspring bear green seeds. The parents must be:

Q85. What fraction of the F2 plants of a monohybrid cross are expected to be heterozygous?

Q86. Two pea plants of unknown genotype are crossed and the offspring come out roughly half tall and half short. The parents must have been:

Q87. A gardener has a tall pea plant of unknown genotype and wants to find out whether it is TT or Tt. Which cross settles it, and how?

Q88. Two Tt parents already have three tall children. The fourth child's chance of tt is:

Q89. Assertion: The recessive trait skips the F1 generation. Reason: Its factor is absent from F1 plants.

Q90. Assertion: Mendel's ratios required counting many offspring. Reason: Inheritance ratios are probabilities that emerge over large numbers.

Q91. A geneticist crosses an unknown tall pea with tt and gets 50% short offspring. The unknown is:

Q92. Which conclusion does the monohybrid cross NOT support?

Q93. Mendel's laws applied to humans suggest a child CAN show a trait neither parent displays if:

Q94. The deepest reason the SAME rules govern peas and humans is that both:

Q95. In the F2 of a monohybrid cross, picking one TALL plant at random, the chance it is pure TT is:

Q96. Give a complete account of Mendel's monohybrid experiment: the choice of material, the cross through F1 and F2 with a Punnett square, both F2 ratios, and the three conclusions about inheritance that follow.

Q97. Explain how Mendel's model accounts for: (a) a trait skipping a generation, (b) two tall parents producing a short child (in pea terms), (c) why a recessive trait is not gradually diluted out of a population, and (d) how a test cross reads hidden genotypes.

Q98. 'Inheritance is particulate, paired and probabilistic.' Justify each of the three adjectives from the monohybrid evidence, and explain what each implies for predicting offspring in practice.

Q99. Design and interpret a full breeding investigation: a gardener has tall pea plants of unknown purity and wants a guaranteed pure-breeding tall line. Lay out the crosses, expected results in every case, the reasoning at each step, and the final verification — with the Mendelian principle used at each stage.

Q100. Which question could the dihybrid cross answer that the monohybrid cross could not?

Q101. Consider these statements about Mendel's dihybrid cross of RRYY with rryy. I. All the F1 plants are RrYy and bear round yellow seeds. II. The F2 shows four phenotypes in the ratio 9 : 3 : 3 : 1. III. Round-green and wrinkled-yellow seeds appear in the F2. IV. Those two combinations were present in one of the original parents. Which statements are correct?

Q102. Which statement best explains what INDEPENDENT INHERITANCE means?

Q103. The dihybrid ratio 9 : 3 : 3 : 1 can be understood as two separate 3 : 1 ratios multiplied together. Within the F2, seed SHAPE alone appears in the ratio:

Q104. How many different kinds of gamete can an RrYy plant produce?

Q105. Assertion (A): New combinations of traits appear in the F2 of a dihybrid cross. Reason (R): The factor pairs separate independently when gametes are formed, so a factor from one parent can be paired with a factor from the other.

Q106. Which sequence correctly describes how a gene produces a trait?

Q107. Which statement best explains, in terms of proteins, why a single dominant factor is enough to produce the dominant trait?

Q108. Consider these statements about chromosomes and genes. I. Genes are located on chromosomes. II. Body cells carry chromosomes in pairs. III. A gamete receives one chromosome of each pair. IV. Fertilisation restores the paired condition. Which statements are correct?

Q109. Why does a dihybrid Punnett square have sixteen cells while a monohybrid one has only four?

Q110. A round green pea plant (RRyy) is crossed with a wrinkled yellow one (rrYY). The F1 plants will be:

Q111. In the height story of pea plants, the tall version of the gene directs the making of an enzyme that produces a growth hormone. A tt plant is short because:

Q112. A plant with the genotype RrYy is described as heterozygous for both traits. This means that:

Q113. Out of 160 plants in a dihybrid F2 generation, the number expected to bear wrinkled yellow seeds is about:

Q114. Why is it more accurate to call a FACTOR dominant than to call an organism dominant?

Q115. Consider what Mendel's dihybrid F2 generation established. I. Each trait pair separates independently of the other. II. New combinations of traits can appear that neither parent showed. III. Each trait on its own still gives a 3 : 1 ratio. IV. Two traits studied together always stay linked. Which statements are correct?

Q116. An RrYy plant is crossed with an rryy plant. The offspring appear in the ratio:

Q117. Which statement best explains why following two traits at once required Mendel to raise far more plants than following one?

Q118. Which statement best explains why a change in a visible trait must ultimately reflect a change in a protein?

Q119. Which statement best explains why genes lying on the SAME chromosome tend to be inherited together?

Q120. An RrYy × rryy test cross yields phenotypes in ratio:

Q121. A breeder wants round-green peas breeding true. The genotype to fix is:

Q122. Assertion: New trait combinations appear in the dihybrid F2. Reason: Factor pairs for different traits segregate independently during gamete formation.

Q123. Assertion: Both parents determine a child's traits equally. Reason: Each parent's gamete delivers one complete chromosome set.

Q124. If Mendel's shape and colour genes had shared one chromosome, F2 would show:

Q125. A round-yellow F2 plant is selfed and yields some wrinkled-green offspring. Its genotype was:

Q126. The gene→protein→trait chain implies a changed trait ultimately reflects:

Q127. How many DISTINCT genotypes exist in the dihybrid F2?

Q128. The deepest unification this topic offers is:

Q129. Present the dihybrid cross as an argument: the setup, the F1, the F2 counts, the logical deduction of independent inheritance from the new combinations, and the confirmation that each trait separately still follows the 3:1 law.

Q130. Explain the complete chain from DNA to a visible trait using the plant-height example, and use it to give chemical meaning to: dominant allele, recessive allele, heterozygote's appearance, and why 'recessive' does not mean 'defective organism'.

Q131. Describe how the behaviour of chromosomes during germ-cell formation and fertilisation provides the physical mechanism for BOTH of Mendel's laws, maintains the species' chromosome number, and guarantees equal parental contribution — with the pea genes as illustration.

Q132. A breeder self-pollinates an F1 round-yellow (RrYy) pea and harvests 320 F2 seeds. Predict the expected number of each phenotype; explain which classes are new combinations and their breeding value; determine which F2 phenotype(s) breed true immediately; and describe how to obtain a true-breeding round-green line.

Q133. Consider these statements about human chromosomes. I. There are 23 pairs in all. II. Twenty-two pairs are matched alike in both sexes. III. The twenty-third pair is the sex chromosomes. IV. All 23 pairs are matched alike in both sexes. Which statements are correct?

Q134. Which statement explains why every egg cell carries an X chromosome, while a sperm may carry either an X or a Y?

Q135. Which statement best explains why the sex of a human child is decided by the father rather than the mother?

Q136. Assertion (A): The Y chromosome is much smaller than the X and carries far fewer genes. Reason (R): Human beings carry twenty-three pairs of chromosomes in each body cell.

Q137. Which statement best explains why about half of all babies born are boys and half girls?

Q138. Why does the cross XX × XY give a 1 : 1 ratio when Tt × Tt gives 3 : 1, though both are crosses of two factors?

Q139. Consider these statements about the sex chromosomes of a child. I. A daughter receives one X from her mother and one X from her father. II. A son receives his X from his mother and his Y from his father. III. The 22 autosome pairs come one from each parent in both cases. IV. A son receives his Y from his mother. Which statements are correct?

Q140. In many turtles and crocodiles, the sex of the hatchlings depends on the temperature at which the eggs were incubated. This shows that:

Q141. A conservationist shades the beaches where turtles nest. The most likely purpose is to:

Q142. Which statement best explains why the biology of sex determination has real social importance?

Q143. A district reports 850 girls for every 1000 boys among young children. Since the biology predicts about 1000 to 1000, this figure most likely reflects:

Q144. In birds, the mismatched pair of sex chromosomes belongs to the female rather than the male. It follows that in birds the sex of the offspring is decided by:

Q145. What do the different sex-determining strategies across species — chromosomes in mammals, the opposite arrangement in birds, temperature in turtles — together suggest?

Q146. The cross XX × XY, written as a Punnett square, gives offspring genotypes in the ratio:

Q147. Assertion (A): A family may have five daughters in succession entirely by chance. Reason (R): Each conception is an independent event with about an even chance of either outcome, and a run of five has a probability of about one in thirty-two.

Q148. A couple has three sons. The probability that their next child will be a daughter is:

Q149. Consider these statements about sex determination in human beings. I. It is settled at fertilisation. II. It is settled by which kind of sperm reaches the egg. III. It cannot be altered by diet, timing or any ritual. IV. It can be influenced by the temperature of the mother's surroundings. Which statements are correct?

Q150. Which statement about sex determination in human beings is TRUE?

Q151. Why is the human sex ratio 1:1 rather than 3:1?

Q152. Assertion: The father's gamete decides the baby's sex. Reason: Eggs all carry X while sperm carry either X or Y.

Q153. Assertion: A family can have five daughters in a row naturally. Reason: Each conception is an independent 50:50 event.

Q154. If Y-bearing sperm were to swim faster than X-bearing sperm in some species, the effect on the sex ratio at birth would be:

Q155. A conservationist shading turtle nests aims to:

Q156. Which chromosome can a son NEVER inherit from his mother?

Q157. The deepest social lesson of this biology is:

Q158. Which statement best explains why the X chromosome carries many genes that have nothing to do with sex?

Q159. Give a full account of human sex determination: the chromosome inventory, gamete formation for each parent, the fertilisation cross with ratio, the identification of the deciding gamete, and the social conclusions this biology enforces.

Q160. Compare the strategies of sex determination across species — human chromosomal XY, bird ZW, reptilian temperature-dependence, and changeable sex in snails — and discuss what this diversity implies about the 'purpose' and flexibility of sex-determining mechanisms.

Q161. 'The 1:1 sex ratio is one of biology's most reliable predictions, yet individual families and some regions deviate from it.' Reconcile this statement fully: the mechanism guaranteeing 1:1, why family-level deviation is normal, why regional deviation is alarming, and the reasoning a science student should deploy against sex-selection myths.

Q162. Trace the sex chromosomes across three generations: maternal grandmother, maternal grandfather, paternal grandmother, paternal grandfather → parents → a grandson and a granddaughter. Identify every possible origin of each grandchild's sex chromosomes and state which ancestors could NOT have contributed them.