Inheritance

Biology, HSSC-KPK Second Year. This chapter is split into 30 topics and has 700 practice questions. The topics covered are listed below, followed by 10 free sample questions from the chapter.

Topics in this chapter

1. Mendel's Laws of Inheritance 30 questions
2. Independent Assortment and Probability 20 questions
3. Exceptions to Mendelian Inheritance 20 questions
4. ABO Blood Group System 30 questions
5. Rh Blood Group System 20 questions
6. Gene Interactions and Epistasis 20 questions
7. Polygenic Inheritance 20 questions
8. Gene Linkage and Crossing Over 20 questions
9. Sex Determination 20 questions
10. Sex Linkage in Drosophila 20 questions
11. Sex Linkage in Humans 20 questions
12. Sex-Related Traits and Comprehensive Review 20 questions
13. Mendel Pea Traits and Historical Facts 25 questions
14. Monohybrid Cross Calculations 24 questions
15. Dihybrid Cross Calculations 28 questions
16. Probability Rules Applied to Genetics 23 questions
17. Dominance Relations and Cross Outcomes 21 questions
18. ABO Crosses and Transfusion Cases 30 questions
19. Rh Crosses and Erythroblastosis Cases 24 questions
20. Epistasis and Bombay Phenotype Cases 22 questions
21. Polygenic Inheritance Computations 29 questions
22. Linkage and Recombination Calculations 28 questions
23. Sex Determination and Sex Ratio Cases 23 questions
24. Drosophila Sex-Linked Crosses and Morgan Data 27 questions
25. Human X-Linked Crosses and Pedigrees 28 questions
26. Sex-Limited and Sex-Influenced Trait Crosses 20 questions
27. Genetics Terms Practical Tests and Exercise Items 20 questions
28. Multi-Gene Probability Problems 26 questions
29. Recessive Trait Carrier Probability Problems 21 questions
30. Blood Group Inheritance Possibilities and Exclusions 21 questions

Sample questions: Inheritance

10 sample questions with the correct answer and an explanation. Try to answer each one before reading the explanation.

Q1. How does incomplete dominance differ from co-dominance?

• A. Co-dominance always produces a blended intermediate phenotype
• B. Both terms describe exactly the same phenomenon
• C. Incomplete dominance produces a blended intermediate phenotype, while co-dominance produces distinct simultaneous expression of both alleles without blending(correct answer)
• D. Incomplete dominance never occurs in nature; only co-dominance is real

Answer: C.Incomplete dominance blends phenotypes (e.g., pink), while co-dominance expresses both alleles distinctly and simultaneously (e.g., AB blood type).

Q2. In a cross showing complete dominance, is there a need for a test cross to distinguish heterozygotes from dominant homozygotes by phenotype alone?

• A. No, because complete dominance never produces heterozygotes
• B. No, because heterozygotes always look different from dominant homozygotes in complete dominance
• C. Yes, because heterozygotes and dominant homozygotes look identical in complete dominance(correct answer)
• D. A test cross is irrelevant to dominance relations

Answer: C.Since heterozygotes and dominant homozygotes are phenotypically identical in complete dominance, a test cross is needed to distinguish them; incomplete dominance avoids this need.

Q3. Why does the real danger of Rh incompatibility occur mainly in subsequent (not first) pregnancies?

• A. Because antibodies are only produced during the second pregnancy, never the first
• B. Because Rh-positive fetuses can only occur in second pregnancies
• C. Because the mother's immune response has already been sensitized from the first exposure, so her antibodies can cross the placenta in later pregnancies and destroy the fetal red blood cells(correct answer)
• D. Because the placenta only forms during the second pregnancy

Answer: C.The first exposure sensitizes the mother's immune system; subsequent pregnancies trigger a stronger antibody response that crosses the placenta.

Q4. How can erythroblastosis foetalis be prevented in a subsequent pregnancy?

• A. The foetus must be delivered prematurely in every pregnancy
• B. The mother must avoid all future pregnancies
• C. The father must be given a blood transfusion
• D. The mother may be injected with anti-Rh antibodies after delivering her first Rh-positive baby(correct answer)

Answer: D.Injecting the mother with anti-Rh antibodies after her first Rh-positive delivery can prevent sensitization and future erythroblastosis foetalis.

Q5. When F1 wheat plants were crossed with each other, F2 grains showed seven shades in a specific ratio. What did this suggest about the initial appearance of incomplete dominance in F1?

• A. It proved the trait was controlled by epistasis alone
• B. It proved the trait was sex-linked
• C. It seemed like incomplete dominance at first, but the F2 ratio revealed multiple genes were involved (polygenic inheritance), not simple single-gene inheritance(correct answer)
• D. It confirmed that only one gene was responsible for the trait

Answer: C.The F1 intermediate colour initially resembled incomplete dominance, but the seven-shade F2 ratio revealed polygenic control by multiple gene pairs.

Q6. Why did Morgan's discovery of eye colour inheritance in Drosophila prove to be 'a most informative trait'?

• A. Because it was the only trait ever studied in Drosophila
• B. Because it clearly demonstrated the association between a specific gene and the X chromosome, establishing the chromosomal theory of inheritance(correct answer)
• C. Because it disproved Mendel's laws entirely
• D. Because eye colour has no connection to genetics at all

Answer: B.The eye colour experiments provided strong evidence linking specific genes to specific chromosomes, supporting chromosomal inheritance theory.

Q7. According to the exercise, a woman with normal colour vision, whose father was red-green colour blind, married a red-green colour-blind man. What is the probability that her first-born child will be red-green colour blind?

• A. 0.50(correct answer)
• B. 0.25
• C. 1.0
• D. 0.025

Answer: A.The woman must be a carrier (X^CX^c, since her father was colour blind); crossed with a colour-blind man (X^cY), offspring have a 0.50 probability of being colour blind.

Q8. In the modified method of symbols, how is the letter for an allele chosen?

• A. From the dominant allele in every case
• B. At random from the whole alphabet
• C. From the name of the scientist
• D. From the abnormal recessive allele, as a for albinism(correct answer)

Answer: D.In the modified method the symbol is chosen according to the abnormal recessive allele, for example a for albinism and A for the normal allele.

Q9. How does anti-Rh injection after the first delivery protect the next baby?

• A. It turns the blood of the baby into Rh-negative blood
• B. It increases the amount of the mother's own anti-Rh antibody
• C. It destroys Rh-positive foetal cells in her blood before she responds(correct answer)
• D. It stops the mother from making any new red blood cells

Answer: C.The injected antibodies destroy the Rh-positive red cells that entered the mother's circulation before her own immune system has been stimulated.

Q10. Which row correctly separates the three terms?

• A. All three terms mean the same thing
• B. Sex-linked: gene on the X; sex-limited: only one sex shows it; sex-influenced: both sexes show it unequally(correct answer)
• C. Sex-linked: both sexes show it unequally; sex-limited: gene on the Y; sex-influenced: gene on the X
• D. Sex-linked: only one sex shows it; sex-limited: gene on the X; sex-influenced: both equal

Answer: B.Sex-linked traits are tied to the X; sex-limited traits appear in only one sex; sex-influenced traits appear in both with different frequency.