Who this is for: Cambridge IGCSE Biology (0610) students who want inheritance — genotype, phenotype, alleles, dominant and recessive — to become reliable marks instead of terms they use interchangeably.
What query it owns: how to understand and revise inheritance in Cambridge IGCSE Biology.
Why this is safe: this page owns the inheritance revision-guide angle, while Tutopiya’s Inheritance subtopic page owns the learning resource and the free Inheritance quiz owns the practice.

Inheritance is the transmission of genetic information from parents to offspring. Cambridge IGCSE Biology (0610) tests whether you can define key genetic terms, distinguish genotype from phenotype, and explain how dominant and recessive alleles determine characteristics. This guide covers the syllabus definitions, the terminology tables examiners expect, and the question types that appear every year.

Key takeaways

• Gene = a length of DNA coding for a specific protein; allele = alternative form of a gene.
• Genotype = the alleles an organism possesses; phenotype = the observable characteristic.
• Dominant allele is expressed even if only one copy is present; recessive allele is expressed only if two copies are present.
• Homozygous = two identical alleles (TT or tt); heterozygous = two different alleles (Tt).
• Use letters to represent alleles — capital for dominant, lower case for recessive.

What is inheritance in Cambridge IGCSE Biology?

Inheritance describes how characteristics are passed from parents to offspring through genes. Each gene may exist in different forms called alleles. An organism’s genotype (genetic makeup) determines its phenotype (observable features). Dominant alleles mask the effect of recessive alleles in heterozygous individuals. Understanding these terms is essential before tackling monohybrid crosses and Punnett squares.

You can read the full explanation, worked examples and notes on Tutopiya’s Inheritance subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
Gene	Section of DNA coding for a protein	”Define gene.”
Allele	Alternative form of a gene	”Define allele.”
Genotype	Genetic constitution (alleles)	“State the genotype of a heterozygote.”
Phenotype	Observable characteristic	”State the phenotype of Tt.”
Dominant / recessive	Expression pattern of alleles	”Explain why the recessive phenotype is hidden.”

Key inheritance terminology

Term	Definition	Example
Gene	Length of DNA coding for one protein	Gene for flower colour
Allele	Alternative version of a gene	Purple allele / white allele
Genotype	Alleles present in an organism	PP, Pp or pp
Phenotype	Expressed characteristic	Purple or white flowers
Homozygous	Two identical alleles	PP or pp
Heterozygous	Two different alleles	Pp
Dominant	Expressed with one or two copies	P (capital letter)
Recessive	Expressed only with two copies	p (lower case letter)

Inheritance in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical inheritance stem
Define	Precise syllabus definition	”Define the term allele.”
State	Short factual answer	”State the genotype of a homozygous dominant individual.”
Explain	Cause and effect	”Explain why a heterozygote shows the dominant phenotype.”
Distinguish	Clear difference	”Distinguish genotype and phenotype.”
Use genetic diagrams	Punnett square / cross	”Use a genetic diagram to show a monohybrid cross.”

Worked exam-style stems (how to answer the wording)

1. “Define the term allele.” An allele is an alternative form of a gene. Mark-scheme reward: alternative form + gene.
2. “Distinguish genotype and phenotype.” Genotype is the alleles an organism possesses; phenotype is the observable characteristic produced by those alleles. Reward: genetic makeup vs expressed feature.
3. “Explain why a heterozygous individual (Tt) shows the dominant phenotype.” The dominant allele (T) is expressed even when only one copy is present; the recessive allele (t) is masked. Reward: dominant masks recessive in heterozygote.

When you can recognise the wording instantly, work the full set on Tutopiya’s Inheritance quiz and drill Monohybrid Inheritance for Punnett square practice.

How inheritance connects to the rest of the syllabus

Inheritance links to Chromosomes, Genes and Proteins (DNA structure), Meiosis (gamete formation) and Sexual Reproduction (variation). The Cambridge IGCSE Biology resource hub links every Inheritance subtopic.

Common mistakes students make

• Using genotype and phenotype interchangeably.
• Calling an allele a gene (a gene has alleles; they are not the same).
• Assigning the wrong letter case — dominant must be capital, recessive lower case.
• Saying a heterozygote is homozygous.
• Describing a recessive allele as “weaker” instead of “only expressed when homozygous”.

When you need more support

If inheritance terminology questions keep costing marks, work through the Inheritance quiz and Chromosomes, Genes and Proteins notes, then get focused help from a Cambridge IGCSE Biology tutor.

Frequently asked questions

Is inheritance hard in Cambridge IGCSE Biology? The terminology is manageable, but marks are lost confusing genotype with phenotype and mislabelling alleles.

What is the difference between a gene and an allele? A gene is a section of DNA coding for a protein; an allele is an alternative version of that gene.

Why use capital and lower case letters for alleles? Capital letters represent dominant alleles; lower case letters represent recessive alleles — a standard convention in genetic diagrams.

How do I revise inheritance effectively? Learn definitions from memory, practise distinguishing genotype and phenotype, then take the Inheritance quiz before monohybrid crosses.

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