Mutations & Genetic Variation (HL IB Biology)

• Differences exist between organisms of the same species
  • These differences are known as variation
  • Examples of variation include:
    • Coat colour in mammals
    • Body length in fish
    • Flower colour in flowering plants
• Variation results from small differences in DNA base sequences between individual organisms within a population
• There are several sources of these differences in DNA base sequences:
  • Mutation
  • Meiosis
  • Random fertilisation during sexual reproduction

Mutations

• The original source of genetic variation is mutation
• Mutation results in the generation of new alleles which can influence evolution of a species
• Mutations that take place in the dividing cells of the sex organs lead to changes in the alleles of the gametes that are passed on to the next generation
  • A new allele may be advantageous, disadvantageous or have no apparent effect
  • An advantageous allele is more likely to be passed on to the next generation because it increases the chance that an organism will survive and reproduce
  • A disadvantageous mutation is more likely to die out because an organism with such a mutation is less likely to survive and reproduce
• Mutations in a species are, in the long term, essential for evolution by natural selection
• Note that a mutation taking place in a body, or somatic, cell will not be passed on to successive generations, and so will have no impact on natural selection
• Mutation is the only source of variation in asexually reproducing species

NOS: Commercial genetic tests can yield information about potential future health and disease risk. One possible impact is that, without expert interpretation, this information could be problematic

• There are two types of genetic testing available
  • Clinical or medical genetic testing
    • This is carried out through healthcare providers such as doctors, nurse practitioners, or genetic counselors
    • Healthcare providers determine which test is needed, order the test from a laboratory, collect the DNA sample, send the DNA sample to a laboratory for testing and analysis, and importantly they share the results with the patient and ensure understanding of the test results and the implications to the individual and their families
  • Commercial genetic testing provides genetic tests marketed directly to customers
    • The test kits can be bought online or in stores
    • Customers send the company a DNA sample and receive their results directly from the genetic company or lab
    • Commercial genetic testing provides people access to their genetic information without necessarily involving a healthcare provider 
    • This can pose some problems
      • Commercially available genetic tests are not scientifically validated and can give inaccurate results
      • Unexpected information that a customer receives about their health, family relationships, or ancestry may be stressful or upsetting
      • People may make important decisions about disease treatment based on inaccurate or misunderstood information from their test results
      • Individuals often are not provided with genetic counseling