Genetics - Competency-Based Question Bank (with Answers)

Section A: Case-Based Questions

Case Study 1: Gregor Mendel crossed a tall pea plant with a dwarf pea plant. F1 were all tall. F2 had both tall and dwarf.

1. Identify the dominant and recessive traits.
   • Answer: Dominant: Tall (T). Recessive: Dwarf (t).
2. Why did the dwarf trait disappear in F1 and reappear in F2?
   • Answer: It was masked by the dominant 'T' allele in F1 (Tt). It reappeared in F2 when two recessive alleles came together (tt).
3. Designing: F2 Punnett square and ratios.
   • Answer: (T, t) x (T, t) -> TT, Tt, Tt, tt. Phenotypic Ratio: 3 Tall : 1 Dwarf. Genotypic Ratio: 1 TT : 2 Tt : 1 tt.
4. If Mendel chose Snapdragon (Incomplete dominance)?
   • Answer: F1 would have an intermediate phenotype (e.g., Pink if parents were Red and White).
5. Why choose the pea plant?
   • Answer: Short life cycle, many contrasting traits, easy to cross-pollinate, produces many offspring.

Case Study 2: Husband is color-blind, Wife has normal vision (father was color-blind). 6. Is color blindness autosomal or sex-linked?

• Answer: Sex-linked (X-linked) recessive.

7. Genotype of the wife.
   • Answer: $X^C X^c$ (Carrier). Since her father was color-blind ($X^c Y$), he must have passed the $X^c$ to her.
8. Creating: Pedigree chart.
   • Answer: [Description: Circle-Square connecting. Husband shaded, Wife half-shaded/dot].
9. Analysis: % chance son will be color-blind.
   • Answer: 50%. The son receives Y from father and either $X^C$ (Normal) or $X^c$ (Color-blind) from mother.
10. Why more common in males?
    • Answer: Males have only one X chromosome. A single recessive allele on the X chromosome is enough to cause the condition.

Section B: Assertion-Reasoning Questions

Directions: (a) Both A/R true, R explains A; (b) Both true, R doesn't explain A; (c) A true, R false; (d) A false, R true.

11. Assertion (A): A heterozygous individual expresses the dominant trait. Reason (R): The dominant allele masks the expression of the recessive allele.
    • Answer: (a) Both A and R are true and R is the correct explanation.
12. Assertion (A): The Law of Independent Assortment holds true for all pairs of characters. Reason (R): Linked genes do not assort independently.
    • Answer: (d) A is false but R is true. (Linked genes are an exception).
13. Assertion (A): Haemophilia is known as "Bleeder's disease". Reason (R): It is an X-linked recessive disorder where blood fails to clot.
    • Answer: (a) Both A and R are true and R is the correct explanation.
14. Assertion (A): Mutation is a sudden change in genes. Reason (R): Changes in gene structure can lead to variations.
    • Answer: (b) Both A and R are true but R doesn't explain the "sudden" nature.
15. Assertion (A): In humans, the father determines the sex of the child. Reason (R): The egg contains X, sperm can carry X or Y.
    • Answer: (a) Both A and R are true and R is the correct explanation.

Section C: Creating and Designing (Application & Analysis)

16. Designing: Dihybrid cross RRYY x rryy.
    • Answer: Gametes: RY and ry. F1: RrYy (Round-Yellow).
17. Creating: Genetic Profile Bbtt.
    • Answer: Genotype: Bb (Heterozygous), tt (Homozygous recessive). Phenotype: Brown eyes (Dominant B), Straight hair (Recessive t).
18. Analysis: 25 short, 75 tall. Can you tell TT from Tt?
    • Answer: No. Both TT and Tt look identical (Tall) due to dominance.
19. Designing: Law of Segregation flowchart.
    • Answer: Parent (Tt) -> Meiosis -> Gamete 1 (T) and Gamete 2 (t) separate.
20. Visualisation: Locus and Alleles.
    • Answer: [Diagram: Two bars. Same spot marked A on one and a on the other].
21. Application: Blood Group AB.
    • Answer: Co-dominance. Both $I^A$ and $I^B$ alleles are expressed equally.
22. Creating: Two sparkling cats have a non-sparkling kitten.
    • Answer: Parents must be heterozygous (Ss). Cross: Ss x Ss -> 25% ss (non-sparkling).
23. Analysis: "Criss-cross inheritance".
    • Answer: Father passes the trait to daughter (carrier), who passes it to her son.
24. Designing: Pedigree checklist.
    • Answer: 1. Do unaffected parents have an affected child? (Recessive). 2. Does every affected child have an affected parent? (Dominant).
25. Creating: Dialogue.
    • Answer: Dominant: "I'm in charge here!" Recessive: "Fine, I'll wait until I meet someone just like me."

Section D: Competency & Critical Thinking

26. Genotype vs Genome.
    • Answer: Genotype: Genetic makeup of an individual for a specific trait. Genome: Total genetic material (all genes) of an organism.
27. Scenario: Test Cross.
    • Answer: Cross with 'tt'. If all offspring tall -> Parent is TT. If 50% tall, 50% dwarf -> Parent is Tt.
28. Critical Thinking: Two blue-eyed parents have a brown-eyed child?
    • Answer: Impossible if blue is recessive and brown is dominant.
29. Application: Sickle Cell Anemia.
    • Answer: Point mutation -> Valine instead of Glutamic acid -> Hb molecules clump -> RBCs become sickle-shaped.
30. Monogenic vs Polygenic.
    • Answer: Monogenic: Controlled by one gene (e.g., Pea height). Polygenic: Controlled by multiple genes (e.g., Human skin color).
31. Diagram Based: Punnett square fill-in.
    • Answer: (Standard 2x2 grid results).
32. Importance of Variation.
    • Answer: Helps species adapt to changing environments, reducing extinction risk.
33. Analysis: Why X-linked recessive rare in females?
    • Answer: Female needs two recessive alleles ($X^h X^h$), requiring an affected father and at least a carrier mother.
34. Competency: 9:3:3:1 ratio.
    • Answer: F2 Phenotypic ratio of a Dihybrid cross. 9 (both dominant), 3 (1st dom), 3 (2nd dom), 1 (both rec).
35. Case: Epigenetics.
    • Answer: Environment affects gene expression without changing the DNA sequence.
36. Creating: "Mendel and Linkage".
    • Answer: True. Linked genes do not separate, so he wouldn't have seen the independent combinations.
37. Designing: Mutation visual aid.
    • Answer: Normal: BEAST. Deletion: BEST. Substitution: FEAST. Duplication: BEEAST.
38. Application: DNA Fingerprinting.
    • Answer: Uses VNTRs (Variable Number Tandem Repeats) which are unique to individuals.
39. Critical Thinking: Blood group different from parents.
    • Answer: Parents A ($I^A i$) and B ($I^B i$) can produce O ($ii$) or AB ($I^A I^B$).
40. Analysis: "Law of Purity of Gametes".
    • Answer: Gametes receive only one allele for each trait during meiosis.

Section E: Advanced Competency

41. Scenario: Pure line of white (recessive).
    • Answer: Just one generation. If the plant is white (tt), it is already pure.
42. Designing: Tongue Rolling study.
    • Answer: Survey classmates, tally "Rollers" vs "Non-rollers", use Punnett square to estimate gene frequencies.
43. Application: Genetic Counseling.
    • Answer: Advice for couples with family history of genetic disorders to understand risks.
44. Creating: Comic strip.
    • Answer: [Description: Alleles T and t moving away during Anaphase I].
45. Case Study: Thalassemia (Carrier x Carrier).
    • Answer: 25% risk of affected child (Major).
46. Multiple Alleles (ABO).
    • Answer: Three alleles ($I^A, I^B, i$) exist in the population for one gene.
47. Critical Thinking: Inbreeding risk.
    • Answer: Increases the probability of harmful recessive alleles coming together in homozygous form.
48. Analysis: Y-linked vs X-linked.
    • Answer: Y-linked (Holandric) passes from father to all sons. X-linked can skip generations via females.
49. Designing: Table of disorders.
    • Answer: Haemophilia (X-linked rec, bleeding), Color-blindness (X-linked rec, vision), Thalassemia (Autosomal rec, anemia).
50. Creating: Mendel's conclusion.
    • Answer: "Heredity is governed by discrete factors that segregate, assort independently, and follow rules of dominance."