JAMB Biology: Genetics Questions and Answers

JAMB Biology: Genetics Questions and Answers

If you are searching for JAMB Biology genetics questions with worked solutions, you are in the right place. Genetics is one of the most consistently tested topics in JAMB Biology, appearing across past papers from the 1980s to the most recent exams. This guide walks you through the key concepts, confirmed past questions with detailed answers, and study strategies — everything you need to approach genetics questions with confidence on exam day.

Why Genetics Is a Must-Know Topic for JAMB Biology

Genetics falls under the Continuity of Life section of the official JAMB Biology syllabus. JAMB Biology contains between 40 and 50 objective questions drawn from across the entire syllabus, and genetics questions appear regularly every year. Topics like Mendel's laws, sickle cell anaemia, blood groups, and sex-linked inheritance are recurring themes that experienced JAMB candidates have learned to expect.

Studying genetics thoroughly is not just about memorising ratios — JAMB questions test your ability to apply concepts to new scenarios. That is why working through past questions with detailed explanations is far more effective than reading notes alone.

The official JAMB Biology syllabus (confirm the current version directly with JAMB at jamb.gov.ng) lists the following genetics sub-topics as examinable:

• Mendel's laws of inheritance
• Monohybrid and dihybrid inheritance
• Sex-linked inheritance (including haemophilia, colour blindness, and baldness)
• Blood group genetics
• Probability in genetics and sex determination
• Application of heredity principles in agriculture and medicine
• Variation in populations

Key Genetics Concepts You Must Know

Before diving into past questions, make sure you have a firm grip on these foundational concepts. JAMB questions are built on them.

Mendel's Laws

Law of Segregation: Every individual carries two alleles for each trait. These alleles separate during the formation of gametes, so each gamete carries only one allele. Offspring inherit one allele from each parent.

Law of Independent Assortment: Genes for different traits are sorted into gametes independently of one another. This is the basis for the dihybrid cross and the 9:3:3:1 ratio.

Monohybrid Inheritance

Monohybrid inheritance involves a single trait controlled by one gene. The classic example is tall (T) vs. short (t) in pea plants.

When two heterozygous parents (Tt × Tt) are crossed:

• Phenotypic ratio (F2): 3 dominant : 1 recessive (3:1)
• Genotypic ratio (F2): 1 TT : 2 Tt : 1 tt (1:2:1)

Dihybrid Inheritance

A dihybrid cross examines two traits at the same time — for example, seed colour (Y = yellow, y = green) and seed shape (R = round, r = wrinkled). When two double heterozygotes (YyRr × YyRr) are crossed:

• Phenotypic ratio (F2): 9:3:3:1
• 9 show both dominant traits
• 3 show first dominant, second recessive
• 3 show first recessive, second dominant
• 1 shows both recessive traits

Incomplete Dominance

When neither allele is fully dominant, the heterozygote shows a blended or intermediate phenotype. The classic JAMB example: red flower × white flower = pink flower.

⚠️ Important note for JAMB candidates: Older JAMB papers (e.g., 1988) may use the term "blending inheritance" while newer papers use "incomplete dominance." Both terms refer to the same result in JAMB's context — a pink offspring from red and white parents. Learn to recognise both terms.

Sex-Linked Inheritance

Sex-linked traits are controlled by genes found on the X chromosome. Because males have only one X chromosome (XY), they are more likely to express sex-linked recessive conditions.

JAMB-tested sex-linked traits include:

• Haemophilia
• Colour blindness
• Baldness

⚠️ Common mistake: Several unofficial revision websites incorrectly list albinism as sex-linked. Albinism is autosomal recessive — it is NOT sex-linked. JAMB consistently tests this distinction.

Sickle Cell Anaemia

Sickle cell anaemia follows an autosomal recessive inheritance pattern. The key genotypes are:

• HbA HbA — Normal (no disease, no trait)
• HbA HbS — Carrier (sickle cell trait, no disease)
• HbS HbS — Affected (sickle cell anaemia)

Blood Groups

Human blood groups (A, B, AB, O) are controlled by 3 alleles: IA, IB, and i. Group O is the universal donor; Group AB is the universal recipient.

⚠️ Some unofficial prep sites state 4 alleles — this is incorrect. The confirmed JAMB answer is 3 alleles.

Confirmed JAMB Genetics Past Questions With Worked Solutions

Below are verified past questions drawn from official JAMB past papers, with full step-by-step solutions.

Question 1 — Sickle Cell Inheritance (JAMB 1997)

The homozygous condition HbS HbS results in sickle cell anaemia, whereas HbA HbS has the sickling trait. What is the probability that a couple both with the sickling trait will give birth to one normal child?

A. ½ B. ¼ C. ¾ D. 1

✅ Answer: B — ¼ (25%)

Worked Solution: Both parents are carriers: HbA HbS × HbA HbS

Offspring: 1 HbA HbA (normal) : 2 HbA HbS (carriers) : 1 HbS HbS (sickle cell disease)

Probability of a normal child = 1 out of 4 = ¼

Question 2 — Sex-Linked Characters

Which of the following characters is NOT sex-linked?

A. Albinism B. Baldness C. Haemophilia D. Colour blindness

✅ Answer: A — Albinism

Explanation: Baldness, haemophilia, and colour blindness are all X-linked traits and are listed in the JAMB syllabus as sex-linked characters. Albinism, however, is caused by an autosomal recessive allele — it is carried on a non-sex chromosome and affects males and females equally.

Question 3 — Incomplete Dominance

A red-coloured flower when crossed with a white-coloured one produced pink flowers. This is an example of:

A. Complete dominance B. Blending inheritance C. Interaction of genes D. Back crossing

✅ Answer: B — Blending inheritance (Incomplete dominance)

Explanation: When neither allele is fully dominant, the heterozygous offspring expresses an intermediate phenotype. Red (RR) × White (rr) = Pink (Rr). This is incomplete dominance. Note: If your JAMB paper uses the option "incomplete dominance" instead of "blending inheritance," select that — both describe the same phenomenon in JAMB's context.

Question 4 — Blood Group Alleles

The number of alleles controlling blood groups in humans is:

A. 3 B. 4 C. 5 D. 2

✅ Answer: A — 3

Explanation: The three alleles are IA (responsible for blood group A), IB (responsible for blood group B), and i (responsible for blood group O). Although there are four possible blood groups (A, B, AB, O), they are produced by combinations of these three alleles.

Question 5 — Genotype vs. Phenotype

The genetic make-up of an organism is described as its:

A. Allele B. Chromosome C. Genotype D. Phenotype

✅ Answer: C — Genotype

Explanation: The genotype refers to the actual genetic composition of an organism (e.g., TT, Tt, tt). The phenotype is the observable physical expression of those genes (e.g., tall or short). JAMB regularly tests this distinction.

Question 6 — Mendel's Method

One reason for the success of Mendel's work is that he:

A. Was the first to carry out research on genetics B. Introduced quantitative and qualitative elements C. Selected two characteristics only at a time for study D. Drew up laws based on knowledge of chromosomes

✅ Answer: C

Explanation: Mendel's genius was in controlling variables. By studying one or two traits at a time (rather than many), he was able to identify clear ratios and patterns. He also chose pea plants with clearly contrasting traits, making results easy to interpret.

Key Genetic Ratios to Memorise for JAMB

These ratios appear directly or indirectly in JAMB questions almost every year:

Study Tips for JAMB Biology Genetics

1. Solve at least 10 years of past questions. The more years you cover, the better you understand JAMB's question style. Themes and concepts repeat regularly.
2. Always read worked solutions, not just answer letters. Understanding the reasoning behind each answer prevents guessing and builds lasting knowledge.
3. Use JAMB-recommended textbooks. Titles listed in the official syllabus include Senior Secondary School Biology by Ndu et al. (Longman), Essentials of Biology by Odunfa (Heinemann), and Modern Biology by Ramalingam.
4. Draw Punnett squares for every inheritance question — even in your head. It takes seconds and eliminates errors.
5. Avoid "expo" and "runz" websites. Many sites claiming to provide JAMB questions in advance are scams designed to take money from candidates. There is no shortcut — consistent practice with real past questions is what actually works.

FAQ: JAMB Biology Genetics

1. How many genetics questions appear in JAMB Biology?

There is no fixed number, but genetics is one of the most regularly tested topics in JAMB Biology. Given that the paper contains 40–50 questions covering the entire syllabus, you can typically expect between 3 and 7 questions on genetics-related topics in any given year. Confirm the exact exam structure for your year directly with JAMB at jamb.gov.ng.

2. Is albinism sex-linked in JAMB Biology?

No. Albinism is autosomal recessive, not sex-linked. It is carried on a non-sex chromosome and can affect both males and females equally. Sex-linked traits tested in JAMB include haemophilia, colour blindness, and baldness.

3. What is the difference between genotype and phenotype?

The genotype is the actual genetic composition of an organism (e.g., Tt or TT). The phenotype is the observable physical characteristic that results from those genes (e.g., tall). Two organisms can have the same phenotype (both tall) but different genotypes (TT and Tt).

4. What phenotypic ratio do I expect from a dihybrid cross?

When two double heterozygous parents (e.g., YyRr × YyRr) are crossed, the expected F2 phenotypic ratio is 9:3:3:1. This is one of the most tested ratios in JAMB Biology genetics.

5. Can two carrier parents have a normal child?

Yes. Using sickle cell as an example: two carrier parents (HbA HbS × HbA HbS) have a 1 in 4 (25%) chance of producing a normal child (HbA HbA), a 2 in 4 (50%) chance of producing a carrier, and a 1 in 4 (25%) chance of producing an affected child. This is a classic JAMB question.

Conclusion: Practise Smarter With PassMate

Genetics is one of the highest-value topics you can master for JAMB Biology. The concepts are logical, the ratios are fixed, and JAMB returns to the same themes year after year — which means targeted practice genuinely pays off.

If you want to go beyond this guide, PassMate gives you access to topic-by-topic JAMB past questions with detailed worked solutions, performance tracking, and AI-powered explanations — all built specifically for Nigerian UTME candidates. Instead of hunting across multiple websites for reliable practice materials, PassMate puts everything you need in one place, so you can study efficiently and walk into your exam prepared.

Start practising genetics and every other JAMB Biology topic today at PassMate.