In the equation p² + 2pq + q² = 1, what does the term 2pq represent?

2pq is the proportion of the population that is heterozygous, and the factor of two appears because the heterozygote can be formed in two ways depending on which parent supplies which allele.

Why must p + q = 1 for a gene with two alleles?

Every allele at that locus must be one or the other, so the two frequencies are proportions of the same whole and must add up to one.

State the conditions that must hold for the Hardy-Weinberg equations to apply.

The population must be large, mating must be random, and there must be no mutation, no migration into or out of the population and no natural selection acting on the gene.

About 1 baby in 2500 is born with cystic fibrosis. Calculate the frequency of the cystic fibrosis allele.

q² = 1 ÷ 2500 = 0.0004, so q = √0.0004 = 0.02, giving an allele frequency of 0.02 or 2%.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

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Patterns of Inheritance

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Population Genetics and Epigenetics

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Population Genetics and Epigenetics

The Hardy-Weinberg principle

3 things to know
Components 01, 02 and 03

Overview

Recall questions on what the principle assumes, what each term of the equation stands for, carrier frequency calculations for recessive conditions, and what a departure from the prediction means.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is the Hardy-Weinberg equation more useful for a recessive condition than for a dominant one?

Key term

What does the Hardy-Weinberg principle state?

Key term

In the equation p² + 2pq + q² = 1, what do p and q represent?

Questions from this subtopic

Each one with the model answer underneath.

1
What does the Hardy-Weinberg principle state?
Model answer
It states that in a large, randomly mating population the allele frequencies and the genotype frequencies stay constant from one generation to the next, provided no other factor disturbs them.
2
In the equation p² + 2pq + q² = 1, what do p and q represent?
Model answer
p is the frequency of the dominant allele and q is the frequency of the recessive allele of the same gene.
3
In the equation p² + 2pq + q² = 1, what does the term 2pq represent?
Model answer
2pq is the proportion of the population that is heterozygous, and the factor of two appears because the heterozygote can be formed in two ways depending on which parent supplies which allele.
4
Why must p + q = 1 for a gene with two alleles?
Model answer
Every allele at that locus must be one or the other, so the two frequencies are proportions of the same whole and must add up to one.
5
State the conditions that must hold for the Hardy-Weinberg equations to apply.
Model answer
The population must be large, mating must be random, and there must be no mutation, no migration into or out of the population and no natural selection acting on the gene.
6
About 1 baby in 2500 is born with cystic fibrosis. Calculate the frequency of the cystic fibrosis allele.
Model answer
q² = 1 ÷ 2500 = 0.0004, so q = √0.0004 = 0.02, giving an allele frequency of 0.02 or 2%.

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