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Subjects · Leaving Cert Biology

Leaving Cert Biology: Genetics

How often Genetics comes up on the Biology papers, every year it was asked, and questions to try.

HL Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

OL Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

June 2027 is the first exam on the new Biology course. These come from the 2016–2026 papers, so read them as a guide.

Genetics, Higher Level(6 marks)

Quick ones on Genetics.

(a)Alternative form of a gene?
  1. Codon
  2. Allele
  3. Chromatid
(b)Genotype with two identical alleles?
  1. Haploid
  2. Heterozygous
  3. Homozygous
(c)Phenotype ratio from Tt x Tt (complete dominance)?
  1. 3 : 1
  2. 1 : 2 : 1
  3. 1 : 1
Show the answers

(a) Allele

(b) Homozygous

(c) 3 : 1

Your turn: Higher Level questions on Genetics.

Higher Level

Asked on 10 of the last 10 Higher Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q13
2025Q12
2024Q15
2023Q13
2022Q3, Q13
2021Q12
2019Q11
2018Q13
2017Q12
2016Q4, Q14

Links open the State Examinations Commission’s paper for that year.

More Genetics questions

Genetics, 2 marks

Physical appearance of an organism?

  1. Genotype
  2. Karyotype
  3. Phenotype
Show the answer

Phenotype

It depends on the genotype and the environment, e.g. height is affected by both genes and diet.

Genetics, 2 marks

Allele that is hidden in the heterozygote?

  1. Codominant
  2. Recessive
  3. Dominant
Show the answer

Recessive

It only shows when there are two copies (e.g. tt). In Tt, the dominant allele masks it.

Genetics, 2 marks

Chance that a child of Aa x Aa is a carrier (Aa)?

  1. 1/2
  2. 1/4
  3. 3/4
Show the answer

1/2

Aa × Aa gives AA, Aa, Aa, aa: 2 out of 4 are carriers, so 1/2. Don't confuse it with the 1/4 chance of being aa.

Ordinary Level

Asked on 10 of the last 10 Ordinary Level papers, most recently in 2026. banker

Every paper, year by year

YearWhere it came up
2026Q12
2025Q12, Q16
2024Q13
2023Q12
2022Q12
2021Q4, Q12
2019Q11
2018Q11
2017Q10
2016Q6, Q10

Links open the State Examinations Commission’s paper for that year.

More Genetics questions

Genetics, 2 marks

A gene that shows its effect even when only one copy is present is called?

  1. Recessive
  2. Haploid
  3. Dominant
Show the answer

Dominant

Dominant dominates. A recessive gene shows only when there is no dominant gene present, so two copies are needed.

Genetics, 3 marks

An organism with two identical genes for a trait, such as TT, is described as?

  1. Haploid
  2. Homozygous
  3. Heterozygous
Show the answer

Homozygous

Homo means same, hetero means different. Homozygous is also called pure-breeding.

Genetics, 3 marks

The genes an organism carries are called its?

  1. Genotype
  2. Phenotype
  3. Habitat
Show the answer

Genotype

Genotype is the genes, phenotype is what you can see. Two plants can look the same but have different genotypes.

Other Biology topics

All of Leaving Cert Biology