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Learning objective
 To understand genetic biodiversity
Success criteria
Learners should be able to demonstrate and apply their
knowledge and understanding of:
(e) how genetic biodiversity may be assessed, including
calculations
To include calculations of genetic diversity within isolated
populations, for example the percentage of gene variants (alleles)
in a genome.
proportion of polymorphic = number of polymorphic gene loci
gene loci
total number of loci
Suitable populations include zoos (captive breeding), rare breeds
and pedigree animals.
Genetic biodiversity
 Alleles – different versions of a gene
 The more alleles present in a population, the more
genetically biodiverse the population.
 Species that contain greater genetic diversity are more
likely to be able to adapt to changes in their
environment. Why?
 More likely to carry an advantageous allele
Factors affecting genetic biodiversity
For genetic biodiversity to increase the number of alleles
in a population must also increase. This can occur
through:
 Mutation – creating a new allele
 Gene flow – transferring alleles form one population to
another through interbreeding
Factors affecting genetic biodiversity
For genetic biodiversity to decrease the number of alleles
in a population must also decrease. This can occur
through:
 Selective breeding - (artificial selection)
 Captive breeding programmes
 Rare breeds
 Artificial cloning - (asexual reproduction)
 Natural selection – alleles coding for less advantageous
characteristics will be lost from the population.
Genetic drift – evolution by chance
 Evolution also occurs due to genetic drift.
 In genetic drift chance decides which alleles are passed on
 Evolution by genetic drift usually has a greater effect in
smaller populations where chance has a greater influence
Genetic drift
 In extreme cases it can lead to chance elimination of
an allele from the population
Genetic bottleneck
 Evolution by genetic drift can have a bigger effect if
there is a genetic bottleneck, e.g. when a large
population suddenly become smaller.
Founder effect
 Where a small number of individuals can create a new
colony, geographically isolated form the original. The
new gene pool is small.
Measuring genetic biodiversity
Measure polymorphism (polymorphic genes have more than
one allele e.g. the immunoglobulin gene determining blood
group).
The proportion of genes that are polymorphic can be
measured using the formula:
proportion of polymorphic = number of polymorphic gene loci
gene loci
total number of loci
Locus (plural – loci) the position of the gene on the chromosome
The greater the proportion of polymorphic gene loci, the greater
the genetic biodiversity with the population
Questions
Describe how genetic biodiversity in a population can
increase (2 marks)
2. Explain why it is advantageous for a species to be
genetically biodiverse (3 marks)
3. A scientist was studying 2 species of Drosophila (flies).
DNA was extracted from each species and 25 gene loci
compared.
For species A, 12 of the loci studied were polymorphic.
For species B, 15 of the loci studied were polymorphic.
Use the data collected to explain which of the species
was more genetically diverse. (4 marks)
1.
Answers
1.
Describe how genetic biodiversity in a population
can increase (2 marks)
Number of alleles in a population must increase (1)
Mutations can create new alleles (1)
Gene flow can introduce new alleles into the
population (1)
Answers
2. Explain why it is advantageous for a species to be
genetically biodiverse (3 marks)
More genetically biodiverse a species is the greater
variation in DNA/number of alleles present (1)
Species more likely to survive a change to the
environment (1)
As there is a higher probability that some members of
the species will have the allele to survive the change
and reproduce (1)
Answers
3.
A scientist was studying 2 species of Drosophila (flies). DNA was
extracted from each species and 25 gene loci compared.
For species A, 12 of the loci studied were polymorphic.
For species B, 15 of the loci studied were polymorphic.
Use the data collected to explain which of the species was more
genetically diverse.
proportion of polymorphic = number of polymorphic gene loci
gene loci
total number of loci
Species A 48% of genes were polymorphic (1)
Species B 60% of genes were polymorphic (1)
Species B more genetically diverse as it has a higher percentage
of polymorphic genes (1)
Therefore more alleles are present (1)