Principles of Inheritance and Variation Mock Test – Class 12 Biology

1. Two inherited conditions are compared. Condition P results from alteration of a single gene and follows a recognisable inheritance pattern in families. Condition Q results from an abnormal chromosome complement visible in a karyotype. How should they be classified?

2. A genetically uniform lineage is maintained without sexual reproduction. After many generations, one descendant contains a heritable allele sequence not found in the original lineage. Which source of variation is necessary to explain the origin of that new allele?

3. Assess the statements listed below about ABO phenotypes.
I. Group AB has a unique genotype in the standard ABO model.
II. Group O has a unique genotype in the standard ABO model.
III. Group A always has a unique genotype.
IV. Group B may correspond to either of two genotypes.

4. An affected female with haemophilia is observed under the simple X-linked recessive model. Which parental combination can produce such a daughter?

5. Read the statements given below.
I. Segregation describes separation of alleles within one gene pair.
II. Independent assortment concerns the relationship between segregation events of different gene pairs.
III. A dihybrid can show normal segregation at each locus while the two loci fail to assort independently.
IV. Independent assortment and segregation are identical names for the same rule.

6. Two cells are analysed after genetic alterations.

Which comparison is most appropriate?

7. A diploid honey bee queen is , and a haploid male contributing sperm carries . Consider an egg from the queen that carries allele . Which pair of outcomes correctly describes that same maternal allele under the two possible developmental routes?

8. A honey bee pedigree shows individual P as a male and Q as P's mother. Q's parents are R, a female, and S, a male. Which relationship is necessarily supported by haplodiploidy?

9. Assertion: A disorder in which one mutated gene causes several distinct phenotypic abnormalities can be pleiotropic even if the gene is inherited in a simple Mendelian manner.
Reason: Pleiotropy describes the number of phenotypic effects influenced by one gene, whereas Mendelian inheritance describes how the allele is transmitted.

10. In a family, two phenotypically unaffected parents have an affected son and an affected daughter. Assuming a simple single-gene model with no new mutation, which inheritance pattern is most directly supported?

11. One disorder is caused by a point mutation in a single autosomal gene, another by loss of one X chromosome, and a third by gain of chromosome . Which classification is correct?

12. A homozygous individual producing surface marker P is crossed with a homozygous individual producing surface marker Q. Every individual displays both P and Q simultaneously. Selfing the gives three phenotypic classes in a ratio. Which explanation best fits both generations?

13. Which sequence correctly describes how a genuinely new allele can enter later patterns of inherited variation?

14. A child has a confirmed karyotype showing trisomy . Family members ask whether the condition should be classified as a dominant or recessive allele disorder. Which response best reflects the genetic evidence?

15. In the simplified additive pigmentation model, is self-crossed. An offspring is known to contain at least contributing dominant alleles among the six allele copies. What is the probability that it contains exactly contributing dominant alleles?

16. 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?

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

18. Four genotype descriptions are classified below. Which classification is biologically consistent with the ABO system?

19. Match each organismal system in Column I with the corresponding chromosomal principle in Column II. Each Column II entry is used once.

20. Two genetic changes are compared. Change P deletes one nucleotide from a gene and alters the reading frame beyond that point. Change Q removes a visible chromosome segment while total chromosome number remains unchanged. How should P and Q be classified?

21. Match each statement in Column I with the most appropriate biological level in Column II. A Column II entry may be reused.

22. Two anaemias are compared. Patient P has markedly reduced synthesis of beta-globin but no statement of an altered beta-globin amino-acid sequence. Patient Q produces beta-globin with the glutamic-acid-to-valine substitution associated with abnormal haemoglobin polymerisation. Which interpretation is most appropriate?

23. Assertion: An independently assorting two-gene cross can often be solved by analysing each locus separately and then combining the required probabilities.
Reason: Under independence, the outcome required at one locus does not change the probability of the specified outcome at the other locus.

24. Red Antirrhinum is crossed with pink . Under incomplete dominance, what fraction of the expected progeny will be pink?

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. Two parents both have blood group A and have already produced a blood group O child. Under the standard ABO model, what is the probability that their next child has blood group A?

27. A heterozygous individual produces gametes by normal segregation. Two gametes are selected independently from a very large pool produced by that individual. What is the probability that both carry ?

28. An sample from selfed heterozygous tall pea plants gives the following genotype counts.

Which interpretation is most consistent with the expected monohybrid pattern?

29. Genetic analysis of one individual reveals a beta-globin point mutation and, independently, a karyotype containing three copies of chromosome . Which interpretation best fits the evidence?

30. In the simplified additive pigmentation model, is self-crossed. Which probability relation follows from the symmetry of allele segregation across the three independently assorting loci?

31. Study the disorder information below.

Which matching is correct?

32. Two homologous chromosome pairs are described. Pair P carries alleles and on its homologues, while pair Q carries and . The orientation of pair P during gamete formation does not determine the orientation of pair Q. Which outcome is predicted under the simple model?

33. In normal human chromosomal sex determination, which symbolic relation correctly represents the two possible fertilisation outcomes?

34. A mutation first creates allele on a chromosome carrying . In a later generation, a recombinant gamete contains together with the unchanged allele. Which interpretation correctly assigns the two genetic events?

35. Review the statements below about thalassemia and sickle-cell anaemia.
I. Thalassemia principally involves reduced synthesis of globin chains.
II. Sickle-cell anaemia principally involves structurally altered beta-globin.
III. Both disorders are treated as autosomal recessive conditions.
IV. Both are defined by gain or loss of an entire chromosome.

36. 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?

37. 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:

38. Suppose two genes that were previously assumed to assort independently are found on the same chromosome and their parental allele combinations occur much more frequently than recombinant combinations. How should the original assumption be revised?

39. A researcher is given a tall pea plant but no information about its parents or progeny. Which conclusion can be made from the phenotype alone under complete dominance?

40. In the self-cross , a graph plots the number of contributing dominant alleles from to on the x-axis and expected offspring frequency on the y-axis. Which qualitative pattern is most consistent with the additive model?

41. A gene exists as alleles , and in a population. An individual simultaneously expresses the distinct effects of and . Which description is required to represent both observations?

42. A woman with blood group A and a man with blood group AB have a child with blood group B. Under the standard ABO model, what is the probability that their next child has blood group A?

43. Consider the statements presented below about incomplete dominance and co-dominance.
I. In incomplete dominance, the heterozygote shows an intermediate phenotype.
II. In co-dominance, both allelic expressions are represented in the heterozygote.
III. Both patterns require permanent blending of the two alleles.
IV. Both patterns differ from complete dominance in heterozygous expression.

44. A linked gene pair shows recombination in a test cross producing offspring. If the two reciprocal recombinant classes occur equally often, how many offspring are expected in each recombinant class?

45. Why does paternal Y transmission have two simultaneous consequences for a human son in an X-linked pedigree?

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

Which conclusion best integrates the observations?

47. A line initially labelled true-breeding for flower colour is self-pollinated repeatedly, but both violet-flowered and white-flowered progeny continue to appear. The most appropriate revision is to:

48. An -bearing sperm from a haemophilic man fertilises an -bearing ovum. What two conclusions can be made simultaneously under the simple human model?

49. Morgan's data showed about recombination for one linked gene pair and about for another. A student concludes that the pair must lie on different chromosome pairs because its recombination value is much higher. Which evaluation is most appropriate?

50. 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.