17.4

Monohybrid inheritance

Cambridge IGCSE Biology (0610)  · Unit 17: Inheritance  · 12 flashcards

Monohybrid inheritance is topic 17.4 in the Cambridge IGCSE Biology (0610) syllabus , positioned in Unit 17 — Inheritance , alongside Chromosomes, genes and proteins, Mitosis and Meiosis.  In one line: Inheritance refers to the transmission of genetic information from parents to offspring, resulting in offspring resembling their parents.

This topic is examined in Paper 1 (multiple-choice) and Papers 3/4 (theory), plus Paper 5 or Paper 6 (practical / alternative to practical).

The deck below contains 12 flashcards — 8 definitions, 3 key concepts and 1 application card — covering the precise wording mark schemes reward.  Use the 8 definition cards to lock down command-word answers (define, state), then move on to the concept and application cards to handle explain, describe and compare questions.

Key definition

Meant by 'inheritance' in biology

Inheritance refers to the transmission of genetic information from parents to offspring, resulting in offspring resembling their parents.

Example: a tall pea plant inherits genes for tallness from its parent plants.

What the Cambridge 0610 syllabus says

2026-2028 syllabus, in our words

What the syllabus expects you to be able to do in this topic, in plain English. Match the command word (Describe, Explain, State, etc.) in your answer to score full marks. For the exact wording, see the official syllabus (PDF).

  1. Describe Describe inheritance as genetic information being passed on from one generation to the next.
  2. Describe Describe genotype as an organism's genetic make-up, including in terms of which alleles it has.
  3. Describe Describe phenotype as the features of an organism that can be observed.
  4. Describe Describe homozygous: having two copies of the same allele for a given gene.
  5. State State that two homozygous individuals with the same alleles will be pure-breeding when bred together.
  6. Describe Describe heterozygous: having two alleles of a given gene that are different.
  7. State State that heterozygous individuals are not pure-breeding.
  8. Describe Describe a dominant allele: one that is expressed whenever the genotype contains it.
  9. Describe Describe a recessive allele: one that is expressed only if the genotype contains no dominant allele of that gene.
  10. Interpret Interpret pedigree diagrams that show how a given characteristic is inherited.
  11. Use Use genetic diagrams for predicting the outcome of monohybrid crosses and for working out phenotypic ratios (limited to ratios of 3:1 and 1:1).
  12. Use Use Punnett squares to work out and show all the possible genotypes from crosses that produce more than one genotype.
  13. Explain Explain how a test cross is used to find out an unknown genotype. Supplement
  14. Describe Describe codominance: when, in a heterozygous organism, the phenotype is affected by both alleles. Supplement
  15. Explain Explain how ABO blood groups are inherited, using the alleles Iᴬ, Iᴮ and Iᵒ and the four phenotypes: blood groups A, B, AB and O. Supplement
  16. Describe Describe what a sex-linked characteristic is: a feature controlled by a gene on a sex chromosome, so that it shows up more often in one sex than the other. Supplement
  17. Describe Describe how red-green colour blindness is an example of a sex-linked characteristic. Supplement
  18. Use Use genetic diagrams for predicting what monohybrid crosses produce when codominance or sex linkage is involved, and work out the phenotypic ratios. Supplement
Definition Flip

What is meant by 'inheritance' in biology?

Answer Flip

Inheritance refers to the transmission of genetic information from parents to offspring, resulting in offspring resembling their parents.

Example: a tall pea plant inherits genes for tallness from its parent plants.
Definition Flip

Define 'genotype' and provide an example.

Answer Flip

Genotype is the genetic makeup of an organism, specifically the alleles it possesses for a particular gene.

Example: a pea plant might have the genotype 'Tt' for plant height, where 'T' represents the allele for tallness and 't' represents the allele for dwarfism.
Definition Flip

What is the 'phenotype' of an organism?

Answer Flip

Phenotype refers to the observable characteristics or traits of an organism, resulting from the interaction of its genotype and the environment.

Example: a pea plant with the genotype 'Tt' might have a tall phenotype.
Definition Flip

Describe the term 'homozygous'.

Answer Flip

Homozygous means having two identical alleles for a particular gene.

Example: a pea plant that has two alleles for tallness (TT) is homozygous dominant, while one with two alleles for dwarfism (tt) is homozygous recessive.
Key Concept Flip

What does it mean for an organism to be 'pure-breeding'?

Answer Flip

A pure-breeding organism is homozygous, meaning it has two identical alleles for a trait. When two identical homozygous individuals breed, they will always produce offspring with the same phenotype for that trait.

Example: crossing two homozygous tall pea plants (TT x TT) will always produce tall pea plants.
Definition Flip

Define 'heterozygous'.

Answer Flip

Heterozygous means having two different alleles for a particular gene.

Example: a pea plant with one allele for tallness (T) and one allele for dwarfism (t) is heterozygous (Tt).
Key Concept Flip

Explain why a heterozygous individual is not pure-breeding.

Answer Flip

A heterozygous individual is not pure-breeding because it carries two different alleles for a trait. This means it can produce gametes with either allele, leading to offspring with different combinations of alleles and thus potentially different phenotypes.

Definition Flip

What is a 'dominant' allele?

Answer Flip

A dominant allele is expressed in the phenotype even when only one copy is present in the genotype.

Example: in pea plants, the allele for tallness (T) is dominant over the allele for dwarfism (t), so a plant with the genotype Tt will be tall.
Definition Flip

Explain what a 'recessive' allele is.

Answer Flip

A recessive allele is only expressed in the phenotype when two copies are present in the genotype (i.e., when the individual is homozygous recessive).

Example: in pea plants, the allele for dwarfism (t) is recessive, so a plant must have the genotype tt to be dwarf.
Key Concept Flip

Describe the purpose of a 'test cross'.

Answer Flip

A test cross is used to determine the unknown genotype of an individual showing a dominant phenotype. It involves crossing the individual with a homozygous recessive individual. The phenotypes of the offspring reveal the unknown genotype.

Definition Flip

Explain 'codominance' with an example.

Answer Flip

Codominance occurs when both alleles in a heterozygous individual contribute to the phenotype.

Example: in shorthorn cattle, the alleles for red coat (CR) and white coat (CW) are codominant. Heterozygous individuals (CRCW) have a roan coat, showing both red and white hairs.
Key Concept Flip

Explain how red-green color blindness is an example of sex linkage.

Answer Flip

Red-green color blindness is a sex-linked trait because the gene responsible for it is located on the X chromosome. Because males only have one X chromosome, they are more likely to express the recessive color blindness allele if they inherit it, while females need to inherit the allele on both X chromosomes.

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17.3 Meiosis 18.1 Variation

Key Questions: Monohybrid inheritance

What is meant by 'inheritance' in biology?

Inheritance refers to the transmission of genetic information from parents to offspring, resulting in offspring resembling their parents.

Example: a tall pea plant inherits genes for tallness from its parent plants.
Define 'genotype' and provide an example.

Genotype is the genetic makeup of an organism, specifically the alleles it possesses for a particular gene.

Example: a pea plant might have the genotype 'Tt' for plant height, where 'T' represents the allele for tallness and 't' represents the allele for dwarfism.
What is the 'phenotype' of an organism?

Phenotype refers to the observable characteristics or traits of an organism, resulting from the interaction of its genotype and the environment.

Example: a pea plant with the genotype 'Tt' might have a tall phenotype.
Describe the term 'homozygous'.

Homozygous means having two identical alleles for a particular gene.

Example: a pea plant that has two alleles for tallness (TT) is homozygous dominant, while one with two alleles for dwarfism (tt) is homozygous recessive.
Define 'heterozygous'.

Heterozygous means having two different alleles for a particular gene.

Example: a pea plant with one allele for tallness (T) and one allele for dwarfism (t) is heterozygous (Tt).

More topics in Unit 17 — Inheritance

Monohybrid inheritance sits alongside these Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.

17.1 Chromosomes, genes and proteins

12 flashcards
17.2 Mitosis

9 flashcards
17.3 Meiosis

9 flashcards

Key terms covered in this Monohybrid inheritance deck

Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.

Meant by 'inheritance' in biology
'genotype' and provide an example
The 'phenotype' of an organism
Describe the term 'homozygous'
'heterozygous'
'dominant' allele
Explain what a 'recessive' allele is
Explain 'codominance' with an example

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