Calculating genetic biodiversity

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Calculating genetic biodiversity
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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.
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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

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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

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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.

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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

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Genetic drift

• In extreme cases it can lead to chance
  elimination of an allele from the population

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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.

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Founder effect

• Where a small number of individuals can create a
  new colony, geographically isolated form the
  original. The new gene pool is small.

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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

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Questions

• Describe how genetic biodiversity in a population
  can increase (2 marks)
• Explain why it is advantageous for a species to
  be genetically biodiverse (3 marks)
• 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)

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Answers

• 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)

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Answers

• 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)

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Answers

• 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)