IGCSE Biology: Inheritance — Practice Questions (Cambridge 0610)

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs — Cambridge International holds copyright in its own papers. Use these alongside the official past papers available from your board.

Each question practises a skill tested in the June 2024 Paper 42. After each answer there is an examiner insight, a mark-scheme insight or a tip, and (where a close match exists) the real question to try next. Questions marked (Extended) test Supplement content.

Tier note: questions marked (Extended) go beyond 0610 Core: sex linkage (17.4), mitosis and meiosis (17.2 and 17.3 are Supplement only), and stem cells and gene expression (17.2, 17.1). All other questions are answerable by a 0610 Core candidate.

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Questions

1. Define the terms gene and allele. [2]

2. A couple already have two daughters and are expecting a third child.

(a) State the sex chromosomes found in the body cells of a male and of a female.

(b) Explain why the chance that the third child is a boy is 50%, whatever the sex of the older children. [3]

3. (Extended) Haemophilia is a sex-linked condition in which blood clots very slowly. The dominant allele Xᴴ gives normal clotting; the recessive allele Xʰ causes haemophilia.

(a) Give the genotype of a man who has haemophilia.

(b) A woman who carries the haemophilia allele but clots normally has children with a man who does not have haemophilia. Calculate the probability that any one of their children will have haemophilia.

(c) Explain why haemophilia is more common in males than in females. [4]

4. In guinea pigs, the allele for black fur (B) is dominant to the allele for white fur (b). Two guinea pigs that are both heterozygous for fur colour are crossed.

(a) State the phenotype of the parents.

(b) State the expected ratio of black to white offspring.

(c) The parents have 12 offspring. Calculate how many of these would be expected to have white fur. [4]

5. (Extended) For each of the following, state whether the nuclear division involved is mitosis or meiosis.

(a) Cells dividing at the tip of a growing root.

(b) Cells in the anther of a flower producing pollen grains.

(c) A zygote dividing to form an embryo.

(d) Cells in the ovary producing egg cells.

(e) A haploid moss plant producing sperm cells. [5]

6. (Extended) An early embryo contains stem cells. Explain how stem cells give rise to specialised cells, and why a nerve cell and a muscle cell from the same person are so different even though they contain the same genes. [4]

7. Define the following terms:

(a) genotype

(b) phenotype

(c) heterozygous. [3]

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Answers

1. Gene: a length of DNA that codes for a protein [1]. Allele: an alternative form of a gene [1].

Examiner insight (Cambridge 0610 June 2024 examiner report, Paper 42, Question 2(d)(i)): Almost all candidates knew the term allele; the most common wrong answer was “genotype”.

Source for the examiner insights on this page: Cambridge IGCSE Biology 0610 June 2024 Principal Examiner Report for Teachers, Paper 0610/42 section, paraphrased.

Try the real question next: Cambridge IGCSE Biology 0610, June 2024, Paper 42, Question 2(d)(i).

2. (a) Male: XY; female: XX [1].

(b) All the mother’s eggs contain an X chromosome [1]. Half the father’s sperm carry an X and half carry a Y, and each fertilisation is a separate chance event, so there is a 1 in 2 (50%) chance of an XY zygote each time [1].

Tip: Each pregnancy is independent: earlier children do not change the odds. A quick genetic diagram (XX × XY) makes the 50% obvious.

Try the real question next: Cambridge IGCSE Biology 0610, June 2024, Paper 42, Question 2(d).

3. (Extended) (a) XʰY [1].

(b) Parents: XᴴXʰ × XᴴY. Offspring: XᴴXᴴ, XᴴY, XᴴXʰ, XʰY [1]. Only XʰY has haemophilia, so the probability is 1 in 4 (0.25 or 25%) [1].

(c) Males have only one X chromosome, so a single recessive allele is expressed; there is no second X to carry a dominant allele that would mask it [1].

Examiner insight (Cambridge 0610 June 2024 examiner report, Paper 42, Question 2(d)(ii)): The most common wrong genotype for a colour-blind male used the dominant allele instead of the recessive one. Check which allele causes the condition before you write the genotype.

Try the real question next: Cambridge IGCSE Biology 0610, June 2024, Paper 42, Question 2(d)(ii).

4. (a) Black fur [1].

(b) Bb × Bb gives BB, Bb, Bb, bb, so the ratio is 3 black : 1 white [1].

(c) One quarter are expected to be white [1]: 12 ÷ 4 = 3 [1].

Tip: Write the parents’ genotypes, their gametes, and a Punnett square every time, even when you think you know the answer. The diagram often earns marks by itself.

5. (Extended) (a) Mitosis [1]. (b) Meiosis [1]. (c) Mitosis [1]. (d) Meiosis [1]. (e) Mitosis [1]: the moss plant is already haploid, so its gametes are produced by mitosis. Meiosis only happens when a diploid cell forms haploid cells.

Examiner insight (Cambridge 0610 June 2024 examiner report, Paper 42, Question 3(a)(i)): Most candidates identified some of the divisions correctly, but only a minority got every one right, so check each step by asking whether the chromosome number halves (meiosis) or stays the same (mitosis).

Try the real question next: Cambridge IGCSE Biology 0610, June 2024, Paper 42, Question 3(a)(i).

6. (Extended) Stem cells are unspecialised cells [1] that divide by mitosis to produce daughter cells that can become specialised [1]. Every body cell contains the same genes, but in each type of cell only some genes are expressed (switched on) [1], so each cell type makes different proteins, which give it its structure and function [1].

Examiner insight (Cambridge 0610 June 2024 examiner report, Paper 42, Question 3(a)(iii)): Many candidates thought specialised cells lack some genes, have different genes, or “make” the genes they need. The genes are all present; the difference is which ones are expressed.

Try the real question next: Cambridge IGCSE Biology 0610, June 2024, Paper 42, Question 3(a)(iii).

7. (a) Genotype: the genetic make-up of an organism in terms of the alleles present [1].

(b) Phenotype: the observable features of an organism [1].

(c) Heterozygous: having two different alleles of a particular gene [1].

Tip: Learn these definitions word for word. Mixing up genotype and allele is one of the commonest ways to drop easy marks.

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Where marks are usually lost

• Confusing allele with genotype.
• Using the dominant allele when writing the genotype of an affected male in a sex-linked cross.
• Assuming every division that produces gametes is meiosis, even in haploid organisms.
• Saying specialised cells have lost genes, instead of saying different genes are expressed.
• Skipping the genetic diagram, which often carries marks of its own.