5.2.1 alleles, phenotypes, and mutations

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Cards (16)

  • Alleles can either be dominant or recessive
  • A dominant allele is always expressed (takes priority over recessive allele). Only one copy is required to be present (BB or Bb).
  • Dominant allele - represented by a capital letter
  • Recessive allele - represented by a lower-case letter
  • Recessive allele requires two copies to be present (bb)
  • Genotype - the combination of alleles present in an organism
  • If two alleles are different, the person is heterozygous for that trait
  • If two alleles are the same, the person is homozygous for that trait
  • Phenotype - observable characteristics of an organism, such as its height, hair colour, or eye colour. Determined by the interaction between the genotype and environment
  • If the allele for a free earlobe is E (dominant) and the allele for an attached earlobe is e (recessive), what will the earlobe of a person with the genotype Ee be like?
    The person is heterozygous. This means that the dominant trait will be observed, and so their earlobe will be free. This assumes that the environment has not interfered.
  • Mutations - a permanent change in the nucleotide sequence of DNA
  • mutations can happen continuously. normally only slightly affect proteins or don't affect them at all. occasionally, mutations may change the structure or shape of a protein
  • Mutations cause
    • undesirable change - harmful to protein function. e.g. substrate may no longer be able to fit the active site.
    • in structural proteins, their strength may be altered
  • Mutations cause
    • survival advantage - more rare. e.g. resistance to an antibiotic in bacteria.
    • these mutations can be beneficial and represent the foundation of evolution by natural selection
  • Some regions of DNA do not encode protein sequences. The term given to these sections is non-coding DNA.
  • In most cases, a characteristic results from multiple genes interacting. However, sometimes, a single gene is responsible for a characteristic. Red/green colour blindness is an example of a characteristic determined by a single gene.