OCR · A-Level · Biology
Course version: H420 · Version from Sept 2025
(e) how genetic biodiversity may be assessed, including calculations
Full specification wording
Biodiversity: (e) how genetic biodiversity may be assessed, including calculations
Genetic biodiversity is the variety of alleles and genes within a species or population.
Checked against the OCR H420 specification (opens in a new tab) on .
- Point 6 of 10
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Genetic biodiversity is the variety of alleles and genes within a species or population. It is assessed by sampling individuals and measuring variation at gene loci, for example by comparing allele frequencies or by counting polymorphic loci. A common measure is the proportion of loci that are polymorphic, and another is heterozygosity, the proportion of individuals heterozygous at a locus. Calculations matter: if 8 of 20 loci sampled are polymorphic, the proportion is 8 ÷ 20 = 0.40, or 40%. If 30 of 200 individuals are heterozygous at a locus, heterozygosity is 30 ÷ 200 = 0.15. Larger, random samples give more reliable estimates, and the same loci must be compared across populations.
What earns the marks
- Genetic biodiversity is the variety of alleles or genes within a species or population.
- Assessment involves sampling individuals and measuring variation at gene loci, such as allele frequencies or the number of polymorphic loci.
- The proportion of polymorphic loci is calculated as polymorphic loci ÷ total loci sampled.
- Heterozygosity can be calculated as heterozygous individuals ÷ total individuals sampled at a locus.
- Worked example: 8 polymorphic loci out of 20 gives 8 ÷ 20 = 0.40, i.e. 40%.
- Worked example: 30 heterozygous individuals out of 200 gives 30 ÷ 200 = 0.15.
- Larger random samples and consistent choice of loci improve the reliability of the estimate.
Common mistakes and how to put them right
Confusing genetic biodiversity with species biodiversity.
Put it right: Genetic biodiversity is variation of alleles within a species, not the number of species present.
Inverting the calculation, for example dividing total loci by polymorphic loci.
Put it right: The correct form is polymorphic loci ÷ total loci sampled.
Assuming a single sample gives a definitive value.
Put it right: Sampling error means larger random samples give more reliable estimates.
Exam tips
- Show the division explicitly before converting to a percentage, so the method is visible.
- Check whether the question asks for a proportion (0 to 1) or a percentage, and label the answer.
- Read the stem carefully to identify which loci or individuals form the numerator and which form the denominator.
Try the lesson
The start of the Biodiversity: (e) how genetic biodiversity may be assessed, including calculations lesson, made from checked teaching notes for this specification point.
Have a go first
A conservation biologist studies genetic diversity in a population of a rare plant. She examines 20 gene loci and finds that 5 of these loci have more than one allele in the population. What is the proportion of polymorphic gene loci in this population?
Listen
Genetic biodiversity is the variety of alleles and genes within a species or population. It is assessed by sampling individuals and measuring variation at gene loci, for example by comparing allele frequencies or by counting polymorphic loci. A common measure is the proportion of loci that are polymorphic, and another is heterozygosity, the proportion of individuals heterozygous at a locus. Calculations matter: if 8 of 20 loci sampled are polymorphic, the proportion is 8 ÷ 20 = 0.40, or 40%. If 30 of 200 individuals are heterozygous at a locus, heterozygosity is 30 ÷ 200 = 0.15. Larger, random samples give more reliable estimates, and the same loci must be compared across populations. A strong answer earns marks for these points. Genetic biodiversity is the variety of alleles or genes within a species or population. Assessment involves sampling individuals and measuring variation at gene loci, such as allele frequencies or the number of polymorphic loci. The proportion of polymorphic loci is calculated as polymorphic loci ÷ total loci sampled. Heterozygosity can be calculated as heterozygous individuals ÷ total individuals sampled at a locus. Exam tip: Show the division explicitly before converting to a percentage, so the method is visible.
Key words
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Genetic biodiversity
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Proportion of polymorphic loci
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Heterozygosity
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Sampling individuals and loci
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See every definition
- Genetic biodiversity
- The variety of alleles and genes within a species or population.
- Proportion of polymorphic loci
- Calculated as polymorphic loci divided by total loci sampled, for example 8 ÷ 20 = 0.40, or 40%.
- Heterozygosity
- The proportion of individuals heterozygous at a locus, calculated as heterozygous individuals divided by total individuals sampled at a locus.
- Sampling individuals and loci
- Measuring variation at gene loci, such as allele frequencies or the number of polymorphic loci, with larger random samples giving more reliable estimates.
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