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Calculating genetic biodiversity

This learning objective focuses on understanding and applying knowledge of genetic biodiversity, including calculations for assessing genetic diversity within isolated populations. Topics covered include alleles, factors affecting genetic biodiversity, genetic drift, and measuring genetic biodiversity.

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Calculating genetic biodiversity

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  1. Calculating genetic biodiversity

  2. Learning objective Success criteria • To understand genetic biodiversity 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.

  3. 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

  4. 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

  5. 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.

  6. 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

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

  8. 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.

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

  10. 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

  11. 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)

  12. 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)

  13. 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)

  14. 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)

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