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O Level Biology Genetics Inheritance Quiz

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Questions

O-Level Biology Quiz - Genetics Inheritance

Name: __________________________
Class: __________________________
Date: __________________________
Score: ______ / 40

Duration: 45 minutes
Total Marks: 40

Instructions:

Answer all questions.
Write your answers in the spaces provided.
For genetic diagrams, clearly show parental genotypes, gametes, and offspring genotypes/phenotypes.
Use standard genetic notation (e.g., capital letters for dominant alleles).

Section A: Multiple Choice (Questions 1–5)

Choose the correct answer for each question. Each question carries 1 mark.

1. Which of the following best defines the term allele?
A. A section of DNA that codes for a protein
B. A pair of genes controlling a characteristic
C. An alternative form of a gene
D. The physical appearance of an organism

Answer: ______

2. In humans, the allele for dimples (D) is dominant to the allele for no dimples (d). A heterozygous man marries a woman with no dimples. What is the probability that their first child will have dimples?
A. 0%
B. 25%
C. 50%
D. 100%

Answer: ______

3. Which of the following statements about mitosis and meiosis is correct?
A. Mitosis produces four genetically different cells.
B. Meiosis produces two genetically identical cells.
C. Mitosis maintains the diploid chromosome number.
D. Meiosis occurs in somatic cells for growth and repair.

Answer: ______

4. A couple has three sons. What is the probability that their next child will be a daughter?
A. 0%
B. 25%
C. 50%
D. 100%

Answer: ______

5. In a certain species of flower, red petals (R) and white petals (W) are codominant. The heterozygous condition results in pink petals. If two pink-flowered plants are crossed, what is the expected phenotypic ratio of the offspring?
A. 1 Red : 2 Pink : 1 White
B. 3 Red : 1 White
C. 1 Red : 1 White
D. All Pink

Answer: ______

Section B: Structured Questions (Questions 6–15)

6. Define the following terms:
(a) Genotype:

_________________________________________________________________________ [1]

(b) Phenotype:

_________________________________________________________________________ [1]

7. Explain the difference between homozygous and heterozygous genotypes, using an example of a gene with alleles B and b.

_________________________________________________________________________ [2]

8. The diagram below represents a pair of homologous chromosomes.

Image pending generation for this question.

(a) State one feature that shows these chromosomes are homologous.
_________________________________________________________________________ [1]

(b) During meiosis, these chromosomes pair up. What is the significance of this pairing?

_________________________________________________________________________ [1]

9. Cystic fibrosis is a genetic disorder caused by a recessive allele (f). The normal allele is dominant (F).
Two parents who do not have cystic fibrosis have a child with the disorder.

(a) State the genotype of the child.
_________________________________________________________________________ [1]

(b) Deduce the genotypes of the parents.
Parent 1: _______________ Parent 2: _______________ [1]

_________________________________________________________________________ [2]

10. Describe the process of mutation.

_________________________________________________________________________ [2]

11. Sickle cell anaemia is caused by a mutation in the gene for haemoglobin.
(a) State one environmental factor that can increase the rate of mutation.
_________________________________________________________________________ [1]

(b) Explain why individuals who are heterozygous for the sickle cell allele have an advantage in areas where malaria is common.

_________________________________________________________________________ [2]

12. The ABO blood group system in humans is controlled by three alleles: $I^A$ , $I^B$ , and $I^O$ .
$I^A$ and $I^B$ are codominant, and both are dominant to $I^O$ .

(a) State the genotype(s) of a person with Blood Group O.
_________________________________________________________________________ [1]

(b) A man with Blood Group AB marries a woman with Blood Group O.
Construct a genetic diagram to show the possible blood groups of their children.


Parental Phenotypes:	AB $\times$ O
Parental Genotypes:	_______________ $\times$ _______________
Gametes:	_______________ $\times$ _______________
Offspring Genotypes:
Offspring Phenotypes:
Ratio:

[4]

13. Variation in humans can be classified as continuous or discontinuous.

(a) Give one example of continuous variation.
_________________________________________________________________________ [1]

(b) Give one example of discontinuous variation.
_________________________________________________________________________ [1]

_________________________________________________________________________ [1]

14. Natural selection is the mechanism for evolution.
Describe the four main stages of natural selection.

[4]

15. Explain why sexual reproduction leads to greater genetic variation in a population compared to asexual reproduction.

_________________________________________________________________________ [2]

Section C: Free Response Questions (Questions 16–20)

16. Haemophilia is a sex-linked condition caused by a recessive allele ( $X^h$ ). The normal allele is dominant ( $X^H$ ).
(a) Explain why haemophilia is more common in males than in females.

_________________________________________________________________________ [2]

(b) A carrier female ( $X^H X^h$ ) marries a normal male ( $X^H Y$ ).
Calculate the probability that they will have a son with haemophilia. Show your working.

_________________________________________________________________________ [2]

17. A farmer wants to breed cows that produce high yields of milk.
(a) Describe how artificial selection (selective breeding) can be used to achieve this.

_________________________________________________________________________ [2]

(b) Suggest one disadvantage of artificial selection compared to natural selection.

_________________________________________________________________________ [1]

18. Down syndrome is a condition caused by a chromosome mutation.
(a) Describe the chromosomal abnormality found in individuals with Down syndrome.

_________________________________________________________________________ [1]

(b) Explain how this abnormality arises during meiosis.

_________________________________________________________________________ [2]

19. Genetic engineering involves transferring genes from one organism to another.
(a) Name the enzyme used to cut DNA at specific sequences.
_________________________________________________________________________ [1]

(b) Name the enzyme used to join DNA fragments together.
_________________________________________________________________________ [1]

_________________________________________________________________________ [1]

20. In a population of beetles, green colour (G) is dominant to brown colour (g).
A sample of the population contains 100 beetles. 16 of them are brown.
Assuming the population is in Hardy-Weinberg equilibrium (note: for O-Level, use simple logic):

(a) What is the genotype of the brown beetles?
_________________________________________________________________________ [1]

(b) If two heterozygous green beetles are crossed, what percentage of the offspring is expected to be brown?
_________________________________________________________________________ [1]

(c) In nature, the number of brown beetles might be higher than expected if they live on tree bark. Explain this using the concept of natural selection.

_________________________________________________________________________ [2]

End of Quiz

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Answers

O-Level Biology Quiz - Genetics Inheritance (Answer Key)

Total Marks: 40

Section A: Multiple Choice

1. C
Explanation: An allele is an alternative form of a gene found at the same locus on a chromosome.

2. C
Explanation: Heterozygous man (Dd) x Woman with no dimples (dd). Offspring: Dd, Dd, dd, dd. 50% have dimples (Dd).

3. C
Explanation: Mitosis produces two genetically identical diploid cells. Meiosis produces four genetically different haploid cells.

4. C
Explanation: The sex of each child is an independent event. The probability of having a boy or girl is always 50% (assuming XY sex determination).

5. A
Explanation: Codominance cross: $R W \times R W$ . Offspring: $RR$ (Red), $RW$ (Pink), $RW$ (Pink), $WW$ (White). Ratio 1:2:1.

Section B: Structured Questions

6.
(a) Genotype: The genetic makeup of an organism (the specific alleles it possesses). [1]
(b) Phenotype: The physical or observable characteristics of an organism (result of genotype and environment). [1]

7.
Homozygous: Having two identical alleles for a trait (e.g., BB or bb). [1]
Heterozygous: Having two different alleles for a trait (e.g., Bb). [1]

8.
(a) They are the same length/shape and carry genes for the same traits at the same loci. [1]
(b) It allows for the exchange of genetic material (crossing over) or ensures that each gamete receives one chromosome from each pair. [1]

9.
(a) ff [1]
(b) Parent 1: Ff, Parent 2: Ff [1]
(c) Both parents are carriers (heterozygous). They each possess one recessive allele (f) which they passed to the child. The child inherited two recessive alleles (ff), expressing the disorder. [2]

10.
A mutation is a random change in the DNA sequence (gene mutation) or chromosome structure/number (chromosome mutation). [2]
(1 mark for "random change", 1 mark for "DNA/chromosome")

11.
(a) Ionising radiation (e.g., X-rays, UV light) or certain chemicals (mutagens). [1]
(b) Heterozygotes have some resistance to malaria. They are less likely to die from malaria than homozygous normal individuals, but do not suffer severe sickle cell anaemia like homozygous recessive individuals. [2]

12.
(a) $I^O I^O$ [1]
(b) Genetic Diagram: [4]

Parental Genotypes: $I^A I^B$ $\times$ $I^O I^O$
Gametes: $I^A, I^B$ $\times$ $I^O$
Offspring Genotypes: $I^A I^O$ , $I^B I^O$
Offspring Phenotypes: Blood Group A, Blood Group B
Ratio: 1:1 (or 50% A, 50% B)
(1 mark for correct parental genotypes, 1 for gametes, 1 for offspring genotypes, 1 for phenotypes/ratio)

13.
(a) Height, weight, skin colour. [1]
(b) Blood group, eye colour, gender. [1]
(c) Continuous variation shows a range of phenotypes (no distinct categories), while discontinuous variation shows distinct categories (few phenotypes). [1]

14.

Variation exists in the population. [1]
Competition for resources / Struggle for survival. [1]
Individuals with advantageous traits survive and reproduce (Survival of the fittest). [1]
Advantageous alleles are passed to offspring, increasing in frequency over generations. [1]

15.
Sexual reproduction involves meiosis (which creates genetic variation via crossing over/independent assortment) and fertilisation (random fusion of gametes). Asexual reproduction involves mitosis, producing genetically identical clones. [2]

Section C: Free Response Questions

16.
(a) Males have only one X chromosome (XY). If they inherit the recessive allele ( $X^h$ ), they express the trait because there is no corresponding allele on the Y chromosome to mask it. Females (XX) need two recessive alleles to express the trait. [2]
(b) Working:
Carrier Female: $X^H X^h$
Normal Male: $X^H Y$
Gametes: $X^H, X^h$ and $X^H, Y$
Offspring: $X^H X^H$ (Normal Female), $X^H X^h$ (Carrier Female), $X^H Y$ (Normal Male), $X^h Y$ (Haemophiliac Male).
Probability of son with haemophilia: 1 out of 4 total offspring, OR 1 out of 2 sons.
Question asks for probability of having a son with haemophilia.
If interpreting "among all children": 25%. If interpreting "among sons": 50%.
Standard O-Level convention: "Probability that they will have a son with haemophilia" usually refers to the specific outcome of a child being both male and affected.
Answer: 25% (or 1/4). [2]
(1 mark for correct diagram/logic, 1 mark for correct probability)

17.
(a) Select cows with high milk yield and bulls from high-yield lines. Breed them. Select the best offspring from the next generation and repeat the process over many generations. [2]
(b) Reduces genetic diversity / Increases susceptibility to disease / Inbreeding depression. [1]

18.
(a) Presence of three copies of chromosome 21 (Trisomy 21). [1]
(b) Non-disjunction during meiosis. Homologous chromosomes (or sister chromatids) fail to separate, resulting in a gamete with an extra chromosome. Fertilisation with a normal gamete results in a zygote with 47 chromosomes. [2]

19.
(a) Restriction enzyme. [1]
(b) DNA ligase. [1]
(c) Concerns about "designer babies" / Unknown long-term health effects / Equity of access / Playing God. [1]

20.
(a) gg [1]
(b) 25% [1]
(c) Brown beetles are better camouflaged on tree bark. Predators (e.g., birds) are less likely to see and eat them. Brown beetles survive and reproduce more often, passing the 'g' allele to offspring. [2]