Principles of Inheritance and Variation Mock Test – Class 12 Biology

1. A diploid species has a normal haploid number of . Cell P contains chromosomes arranged as three complete sets of . Cell Q contains chromosomes because one chromosome type is present in an additional copy. How should P and Q be classified?

2. An inheritance investigation produces the following observations: a recessive phenotype reappears after being hidden in ; linked loci show parental excess with some recombinants; a descendant contains a newly altered allele; and another individual carries an extra chromosome . Which interpretation best integrates all four observations?

3. Parents with genotypes and have a child. Given that the child is not blood group O, what is the probability that the child is blood group AB?

4. A heterozygous monohybrid shows an intermediate phenotype, yet its two alleles segregate into gametes in equal expected proportions. Which classification best describes this situation?

5. Assertion: A colour-blind father cannot transmit his colour-blindness allele directly to his son.
Reason: A father contributes the Y chromosome, rather than his X chromosome, to a son.

6. A breeder begins with a sexually reproducing plant population that already varies in seed size. For several generations, only plants producing larger seeds are chosen as parents, and the average seed size of the selected line increases. No mutagenic treatment is used. Which interpretation is most appropriate?

7. Sturtevant compares recombination frequencies between several linked gene pairs rather than relying only on whether recombinant progeny are present. What additional inference does this approach make possible?

8. A carrier woman is considered in two crosses: first with a normal man , and then with a haemophilic man . Which probability remains unchanged between the two crosses?

9. In a monohybrid cross for pea stem height, true-breeding tall plants are represented as and true-breeding dwarf plants as . Under complete dominance, the expected relation is:

10. Assertion: Sickle-cell anaemia and beta-thalassemia can share an autosomal recessive inheritance pattern without having the same primary molecular defect.
Reason: Sickle-cell anaemia involves a qualitative alteration of beta-globin, whereas beta-thalassemia principally involves reduced synthesis of beta-globin.

11. A text pedigree states that female P and male Q are a couple. Their daughter R has a son S with male T. Which relationship is necessarily correct?

12. In one linkage experiment, only test-cross progeny are obtained and all belong to the two parental classes. A student concludes that recombination between the genes is absolutely impossible. Which interpretation is stronger?

13. Two pea plants are both tall. Genetic analysis shows that one is and the other is . This observation most directly demonstrates that:

14. In honey bees, which symbolic relation correctly represents the basic haplodiploid pattern?

15. Three heterozygous self-crosses involve the same genotype segregation but different heterozygous expression.

Which conclusion best integrates the observations?

16. A reciprocal version of the simple pea stem-height cross is made: first, a true-breeding tall plant provides ovules and a true-breeding dwarf plant provides pollen; then the parental sexes are reversed. Under the same Mendelian assumptions, the two crosses are expected to produce:

17. Match each genetic term in Column I with the most appropriate description in Column II. Each Column II entry is used once.

18. Examine the statements below.
I. A dominant phenotype does not always identify a unique genotype.
II. Under incomplete dominance, a heterozygote can often be recognised from its phenotype.
III. In co-dominance, both allelic effects may be expressed in a heterozygote.
IV. Multiple allelism means a diploid individual normally carries every allele that exists at that locus in the population.

19. A male has normal red-green colour vision despite having a father who is colour blind. Which statement about direct X-chromosome transmission is correct?

20. Arrange the events leading to a female honey bee in the correct order.
P. A queen produces a haploid egg.
Q. A sperm contributes a paternal haploid chromosome set.
R. Fertilisation restores diploidy.
S. The diploid individual develops as a female.

21. Choose the sequence that correctly relates a heterozygous parental genotype to formation of a diploid offspring genotype.

22. Three linked gene pairs show the following recombination percentages.

Which combined ordering is consistent with these data?

23. A carrier woman and a normal man have a child who is known to be colour blind. Under the simple X-linked recessive model, what is the probability that this affected child is male?

24. A haploid honey bee male carries allele . He mates with a diploid queen of genotype . Assuming ordinary segregation in the queen and no mutation, what is the probability that a daughter produced by fertilisation is ?

25. Consider the statements presented below about honey bee inheritance.
I. A male develops from an unfertilised egg.
II. A male can have a maternal grandfather but no father.
III. A diploid heterozygous female can segregate alternative alleles into eggs.
IV. A haploid male must reduce his chromosome number by half during ordinary sperm formation.

26. Assertion: The AB blood-group phenotype is an example of co-dominance.
Reason: In genotype , both and contribute to the expressed phenotype.

27. An population has three phenotypic classes in an approximate ratio. The heterozygous individuals are visibly intermediate between the two homozygotes. Which explanation best fits the observations?

28. Examine the statements given below about honey bee haplodiploidy.
I. Females arise from fertilised eggs.
II. Males arise from unfertilised eggs.
III. Males are haploid and females are diploid.
IV. Male bees produce sperm through the same ploidy-reduction requirement as ordinary diploid males.

29. Haemophilia is described as an X-linked recessive disorder in which:

30. A pink Antirrhinum plant is crossed with a white plant . What phenotypic relation is expected among the progeny?

31. In the additive pigmentation model, is crossed with . What is the probability that an offspring has exactly contributing dominant alleles?

32. Compare the sex-determination systems below.

Which conclusion is correct?

33. In Antirrhinum, is red, is pink and is white. Two pink plants are crossed. An offspring is selected only from the non-red progeny. What is the probability that the selected plant is white?

34. In an cross with independent assortment, what is the probability that an offspring is ?

35. Study the classifications below for pea stem height under complete dominance.

The correct entries for P and Q are:

36. Consider the following features associated with Down's syndrome .
I. Trisomy of chromosome
II. Broad palm with a characteristic crease
III. Delayed physical, psychomotor and mental development
IV. Loss of one X chromosome producing

37. Consider three chromosome abnormalities:
P. Trisomy
Q.
R.
Which classification is correct?

38. Match each chromosome-number condition in Column I with its defining relation in Column II. Each Column II entry is used once.

39. Morgan observed that different linked gene pairs showed different recombination frequencies. Sturtevant then used recombination values to arrange genes relative to one another on chromosomes. Which reasoning provides the critical bridge between the two findings?

40. Use the following arrangement. Homologue P carries alleles and at two different loci, while its partner Q carries and at the corresponding loci. Which conclusion is biologically justified by this arrangement alone?

41. A graph has gene pairs P, Q and R on the x-axis and recombination percentage on the y-axis. Their bars are , and , respectively. If comparable test crosses are performed, which parental-excess pattern is expected?

42. A heterozygous self-cross has genotype ratio . Under complete dominance, the phenotypic ratio is . If the same alleles instead show incomplete dominance while segregation remains unchanged, what phenotypic ratio is expected?

43. Two parents have blood groups A and B, and they produce a child with blood group O. What must be true of the parental genotypes?

44. Assertion: Incomplete dominance changes the phenotypic ratio compared with complete dominance.
Reason: In both cases, alleles of a heterozygote can still segregate normally into different gametes.

45. A honey bee queen has chromosome number . Under normal haplodiploid reproduction, how many chromosomes are expected in an unfertilised egg that develops into a male?

46. In the cross , complete dominance and independent assortment apply. An offspring is known to be round and yellow. What is the probability that its genotype is ?

47. Examine the statements given below about multiple alleles.
I. More than two allelic forms of one gene may exist in a population.
II. A diploid individual normally carries only two alleles at that locus.
III. Multiple allelism requires one person to carry every allele present in the population.
IV. The ABO system illustrates multiple alleles.

48. Study the classifications below.

Which row fails to keep both listed traits within the stated character?

49. Two linked gene pairs are studied in equal-sized test-cross populations. Pair P shows recombinant offspring, whereas pair Q shows . A graph plots parental percentage on the y-axis for the two pairs. Which pattern is expected?

50. If the seed-shape and seed-colour loci assort independently, an plant is expected to form which complete set of gamete types?