An allele is one of the different versions of a particular gene.

How many alleles of each gene does an individual normally have?

Two, one inherited from each parent.

Explain why individuals of the same species show differences in their inherited characteristics.

They inherit different combinations of alleles, and different alleles produce different versions of a characteristic.

What happens to the characteristic when an individual inherits two different alleles of a gene?

If one allele is dominant and the other recessive, only the dominant allele is expressed in the characteristic.

Explain how a person can carry an allele that does not show in their appearance.

A recessive allele is masked whenever a dominant allele of the same gene is also present.

Two pea plants both have round seeds but only one of them can produce wrinkled-seeded offspring. Explain this.

That plant carries one round allele and one wrinkled allele, so it can pass the wrinkled allele on.

Edexcel GCSE Combined Science Biology 1SC0

Key Concepts in Biology

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Cells and Control

Topic overview Mitosis and the cell cycle Why mitosis matters: growth, repair and cancer Growth, differentiation and percentile charts Stem cells and their use in medicine Neurones, receptors and the reflex arc

Genetics

Topic overview Meiosis and the formation of gametes DNA structure, genes and the genome Extracting DNA from fruit Alleles, genotype and phenotype Monohybrid crosses and sex determination Probability and ratios from genetic crosses Causes of variation: genes and environment The Human Genome Project Genetic variation and the effects of mutation

Natural Selection and Genetic Modification

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Health, Disease and the Development of Medicines

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Plant Structures and Their Functions

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Animal Coordination, Control and Homeostasis

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Exchange and Transport in Animals

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Ecosystems and Material Cycles

Topic overview Levels of organisation and interdependence Abiotic and biotic factors in a community Parasitism and mutualism Sampling with quadrats and transects Estimating population size from field data Human impact on ecosystems and biodiversity The carbon cycle The water and nitrogen cycles

Genetics

Alleles, genotype and phenotype

3 things to know
Paper 1

Overview

Alleles and why individuals of a species differ, dominant and recessive alleles and how a recessive allele can be carried unseen, chromosomes and genes, homozygous and heterozygous, genotype and phenotype, gametes and zygotes, and why one phenotype can hide different genotypes.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How do a gene and an allele differ, when is an allele dominant or recessive, and what does homozygous mean?

Key term

What do heterozygous, genotype, phenotype and gamete each mean?

Key term

What is an allele?

Questions from this subtopic

Each one with the model answer underneath.

1
What is an allele?
Model answer
An allele is one of the different versions of a particular gene.
2
How many alleles of each gene does an individual normally have?
Model answer
Two, one inherited from each parent.
3
Explain why individuals of the same species show differences in their inherited characteristics.
Model answer
They inherit different combinations of alleles, and different alleles produce different versions of a characteristic.
4
What happens to the characteristic when an individual inherits two different alleles of a gene?
Model answer
If one allele is dominant and the other recessive, only the dominant allele is expressed in the characteristic.
5
Explain how a person can carry an allele that does not show in their appearance.
Model answer
A recessive allele is masked whenever a dominant allele of the same gene is also present.
6
Two pea plants both have round seeds but only one of them can produce wrinkled-seeded offspring. Explain this.
Model answer
That plant carries one round allele and one wrinkled allele, so it can pass the wrinkled allele on.

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Key Concepts in Biology

Cells and Control

Genetics

Natural Selection and Genetic Modification

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