WAEC / WASSCE
WAEC Biology Genetics Practice Questions, Fully Answered
WAEC past questions cannot legally be republished, so these five genetics questions are original but written in the exact WASSCE format: a monohybrid cross, sex linkage, definitions, a pedigree and blood groups. Each answer uses the phrasing WAEC markers reward, with a tip on where candidates typically drop marks.
Genetics is one of the highest-yield topics in WAEC Biology and one of the worst answered, going by the chief examiners' own reports. This page gives you five original questions in the WASSCE style, each solved in full using the layout and wording markers look for. A note on honesty: I sit Cambridge exams, not WAEC, so nothing here is exam-hall memory. It comes from working through the WASSCE Biology syllabus, the paper format and several years of chief examiners' reports. And because real past questions are copyrighted, every question below is original, matched to the real papers in topic, difficulty and structure.
Where genetics sits in the WAEC Biology exam
WASSCE Biology comes in three papers. Paper 1 is 50 objective questions, Paper 2 is the essay paper, and Paper 3 tests practical work. Genetics lives mainly in Papers 1 and 2. In the objective paper you get quick items: identify the genotypic ratio of a cross, pick the correct definition of an allele, or work out the possible blood groups of children in one step. In the essay paper, genetics arrives as a full question or half a question with labelled parts, typically a cross to draw and interpret, definitions to state in contrast, and a ratio or probability to calculate. The syllabus area is heredity and variation: dominant and recessive traits, monohybrid inheritance, codominance in the human ABO blood groups, sex determination, and sex-linked characters such as haemophilia and colour blindness. Chief examiners' reports say genetics questions are attempted in large numbers but scored poorly, which means a clean, well-laid-out answer genuinely stands out.
Drawing genetic crosses the way markers want
A genetic cross in WAEC Biology is marked line by line, so the layout is worth learning as a fixed routine. Start with the parental phenotypes, written in words. Under them, the parental genotypes. Next line, the gametes, and circle each one: the circle shows you know a gamete carries a single allele, and marking schemes regularly attach a mark to it. Then show fertilisation, either with crossing lines or a Punnett square, and write the offspring genotypes. Finish with the offspring phenotypes and the ratio stated with labels, for example 3 black : 1 white, not a bare 3:1 floating alone. Use one letter for the gene, capital for dominant and small for recessive, and state at the start which allele is which. In sex-linked crosses, put the allele on the chromosome, written XH or Xh, never a bare H and h, because the point being tested is that the gene rides on the X chromosome.
Mistakes chief examiners keep reporting
WAEC publishes chief examiners' reports after each series, and the genetics complaints repeat almost yearly. Candidates confuse gene with allele and genotype with phenotype, so definition marks vanish in pairs. Crosses are drawn without gametes, with gametes left uncircled, or with two different letters used for one gene, which makes the offspring line meaningless. Ratios are stated without phenotypes attached, or a probability is given as a ratio when a fraction was demanded. In sex-linkage questions, many candidates write Hh instead of placing the alleles on the X chromosome and lose most of the question at a stroke. In blood group questions, naming IA and IB as codominant earns credit, while vague phrases like both are strong earn nothing. The fix is mechanical rather than clever: define both terms of every pair in contrast, follow the fixed cross layout every single time, and end every cross with phenotypes plus a labelled ratio. The five solutions above model exactly that phrasing.
Worked questions, step by step
In guinea pigs, black coat colour (B) is dominant to white (b). A homozygous black guinea pig is crossed with a white one. (a) State the genotype and phenotype of the F1 offspring. (b) If two F1 offspring are crossed, work out the phenotypic ratio of the F2 generation, showing the cross in full.
- (a) Write the parents as BB (black) x bb (white). Homozygous means both alleles are identical, and white must be bb because it is recessive.
- List the gametes: every gamete from BB carries B, every gamete from bb carries b. Meiosis places one allele of the pair into each gamete.
- All F1 offspring are Bb and all appear black. The dominant B allele masks b in the heterozygote.
- (b) Cross F1 x F1, which is Bb x Bb, with each parent producing B and b gametes. Circle the gametes when drawing this.
- Combine the gametes: the offspring genotypes are BB, Bb, Bb and bb, a genotypic ratio of 1 BB : 2 Bb : 1 bb.
- State the phenotypes with labels: 3 black : 1 white. BB and Bb both look black, and only bb is white.
Answer: (a) F1 all Bb, all black (b) F2 phenotypic ratio 3 black : 1 white (genotypic ratio 1 BB : 2 Bb : 1 bb)
Where marks slip: WAEC allocates separate marks to parental genotypes, circled gametes, offspring genotypes and the labelled phenotypic ratio, so skipping the gamete line quietly loses a mark even when the final ratio is right.
Try one yourself: In mice, grey fur (G) is dominant to albino (g). A heterozygous grey mouse is crossed with an albino mouse. Show the cross and state the expected ratio of offspring. (Answer: 1 grey : 1 albino)
Haemophilia in humans is controlled by a recessive allele carried on the X chromosome. A woman who is a carrier for haemophilia marries a man with normal blood clotting. (a) Give the genotypes of the couple. (b) Work out what proportion of their sons is expected to have haemophilia. (c) State, with a reason, whether any of their daughters could have haemophilia.
- (a) Write the mother as XHXh and the father as XHY. Sex-linked alleles must be shown attached to the X chromosome, and Y carries no allele for this gene.
- List the gametes: the mother produces XH or Xh, the father produces XH or Y. Circle all four when drawing the cross.
- Combine them: the possible children are XHXH (normal daughter), XHXh (carrier daughter), XHY (normal son) and XhY (son with haemophilia).
- (b) Of the sons, half receive Xh from the mother, so 1/2 of sons are expected to have haemophilia. A son's only X chromosome always comes from his mother.
- (c) No daughter can be affected, because every daughter receives XH from the father, though half the daughters are expected to be carriers. An affected daughter would need Xh from both parents.
Answer: (a) Mother XHXh, father XHY (b) 1/2 (50 percent) of sons (c) no affected daughters, but half are expected to be carriers
Where marks slip: Writing the genotypes as bare Hh instead of on the X chromosome (XHXh) is the single error WAEC reports most often here, and it usually costs the whole cross.
Try one yourself: Red-green colour blindness is X-linked recessive. A colour-blind man marries a woman carrying no allele for the condition. What proportion of their daughters will be carriers, and will any child be colour blind? (Answer: all daughters are carriers; no child is colour blind)
Distinguish clearly between the members of each of the following pairs of genetic terms: (a) gene and allele (b) genotype and phenotype (c) dominant allele and recessive allele.
- (a) A gene is a unit of heredity, a segment of DNA occupying a fixed position on a chromosome and controlling a character, whereas an allele is one of the alternative forms of that gene. Both halves must appear for the pair mark.
- (b) Genotype is the genetic constitution of an organism, the set of alleles it carries, whereas phenotype is the observable physical or physiological appearance produced by the genotype interacting with the environment. Mentioning the environment strengthens the phenotype half.
- (c) A dominant allele expresses itself in both the homozygous and the heterozygous state, whereas a recessive allele expresses itself only in the homozygous state. Avoid the word stronger, which markers do not credit.
Answer: Three contrasting definitions as set out in the steps, each pair defined with a linking word such as whereas
Where marks slip: WAEC gives the mark for the contrast, not for one term alone, so a perfect definition of gene with nothing on allele scores zero for that pair.
Try one yourself: Distinguish between homozygous and heterozygous, giving one example genotype of each. (Answer: homozygous means two identical alleles, for example TT or tt; heterozygous means two different alleles, for example Tt)
A man and his wife both have normal skin pigmentation. Of their four children, three have normal pigmentation but one daughter is albino. Using suitable symbols, (a) state with a reason whether the allele for albinism is dominant or recessive, (b) give the genotypes of the parents and of the albino daughter, (c) calculate the probability that their next child will be albino.
- (a) The allele is recessive, because both parents show normal pigmentation yet produced an albino child; if the allele were dominant, at least one parent would show the condition. The reason must be stated to earn the mark.
- (b) Let A represent normal pigmentation and a represent albinism. The albino daughter must be aa, since a recessive character only shows when homozygous.
- Each parent gave her one a allele but appears normal, so both parents are Aa. Unaffected parents of an affected child are carriers by definition.
- (c) Cross Aa x Aa: the offspring genotypes come out 1 AA : 2 Aa : 1 aa, so the probability of an albino child is 1/4. Each pregnancy is an independent event, so earlier children do not change this.
Answer: (a) Recessive, because unaffected parents produced an affected child (b) both parents Aa, albino daughter aa (c) 1/4
Where marks slip: Candidates commonly write recessive with no reason and lose that mark, and giving part (c) as a ratio like 1:3 instead of the probability 1/4 loses another.
Try one yourself: Two parents with normal hearing have a child with an inherited form of deafness caused by a recessive allele. Give the parents' genotypes and the probability that their next child is deaf. (Answer: both parents Dd; probability 1/4)
A man of blood group AB marries a woman of blood group O. (a) Give the genotypes of the couple. (b) Using a suitable cross, determine the possible blood groups of their children. (c) Explain why none of their children can belong to group AB or group O.
- (a) The father is IAIB and the mother is ii. Group AB carries the two codominant alleles IA and IB, while group O is homozygous for the recessive allele i.
- List the gametes: the father produces IA or IB, the mother produces only i. Circle them in the drawn cross.
- (b) Combine the gametes: the children can be IAi, which is group A, or IBi, which is group B, in a ratio of 1 group A : 1 group B.
- (c) No child can be group AB because the mother cannot supply an IA or IB allele, and no child can be group O because the father always supplies IA or IB while group O requires two i alleles.
Answer: (a) Father IAIB, mother ii (b) group A (IAi) or group B (IBi) in a 1 : 1 ratio (c) as explained: the mother cannot give IA or IB, and the father cannot give i twice over
Where marks slip: Naming IA and IB as codominant earns a specific mark, while loose wording like both alleles are equally strong earns nothing, so use the technical term.
Try one yourself: A heterozygous group A man (IAi) marries a heterozygous group B woman (IBi). What blood groups are possible among their children? (Answer: all four groups, A, B, AB and O, in equal proportions)
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Where can I get genuine WAEC Biology past questions on genetics?
WAEC runs an official e-learning platform with a bank of past questions and chief examiner feedback, and licensed past-question booklets are sold widely across West Africa. Free PDFs circulating on social media are often mislabelled or missing diagrams. The five questions on this page are original but written to match the real format, so they are safe to practise from alongside official material.
Do I have to use a Punnett square, or can I draw crossing lines?
Either is accepted. WAEC marks the same points regardless: parental genotypes, circled gametes, offspring genotypes, and phenotypes with a labelled ratio. A Punnett square is safer in blood-group or dihybrid crosses because it keeps the combinations tidy, but a neat line cross earns full marks in a monohybrid question. Whichever you pick, never skip the gamete line.
Does genetics appear in the WAEC practical paper?
Rarely as a direct practical. Paper 3 concentrates on specimens, biological drawings and experiments, but variation can surface there, for example classifying continuous and discontinuous variation from data such as heights or fingerprint patterns. The genetics you revise for definitions, crosses and probability calculations is examined almost entirely in the objective and essay papers.
What symbols should I use for blood group alleles?
Use IA, IB and i, writing the A and B raised against the capital I in your script. State at the start that IA and IB are codominant and that i is recessive to both; that single sentence is regularly worth a mark before the cross is even drawn. Some textbooks write IO instead of i, and WAEC accepts that too if used consistently.