Unit 4: Section 4- Evolution

A summary of section 4 of edexcel A2 biology

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  • Created by: R_Hall
  • Created on: 11-01-14 17:54

Evolution, Natural Selection and Speciation

  • Gene pool- complete range of alleles in a population. New alleles generated through mutation
  • Allele frequency is how often an allele occurs in a population, and evolution is the change in allele frequency over time
  • Individuals vary because of differences in alleles, meaning some are better adapted. Individuals with a beneficial allele are more likely to survive, reproduce and pass on their alleles. A greater population of the next generation inherit the beneficial allele. They in turn are more likely to survive and pass on the alleles, so frequency of the beneficial allele increase. This is natural selection
  • Speciation is the development of a new species, and occurs when populations of the same species become reproductively isolated
  • Ways changes in phenotype prevent populations successfully breeding- seasonal changes (individuals develop different mating seasons ect), mechanical changes (changes in genitalia) and behavioural changes (individuals develop new courtship rituals)
  • A population becomes reproductively isolated due to geographical isolation or random mutations. Random mutations result in the above phenotype changes
  • Geographical isolation occurs when a physic barrier divides populations. Conditions on either side are different, and different characteristics become more common due to natural selection. The individuals become so different that the groups become two different species
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Evidence for Evolution

  • DNA evidence- Theory suggests all organisms evolved from shared common ancestors, and closely related species diverged more recently. Evolution is caused by gradual changes in the base sequence of organisms' DNA. 
  • Scientists found that organisms which diverged from each other recently have more similar DNA as less time has passed for changes in DNA sequence to occur
  • Proteomics (study of proteins)- Related organisms have similar DNA sequences and so similar amino acid sequences in their proteins
  • Scientists found that organisms which diverged from each other recently have more similar proteins as less time has passed for changes to occur
  • The scientific community validates evidence about evolution. Scientists share and discuss their work in three main ways
  • 1. Scientific journals- publish articles describing their work, allowing other scientists to repeat their experiments and see if they get the same results using the same methods. If the results can be replicated, the community are confident that the evidence is reliable
  • 2. Peer review- before publishing in a journal, other scientists who work in the area review the work to check that it is valid and that it supports the conclusions
  • 3. Conferences- meetings scientists attend to discuss work. Scientists with important/interesting results present their work and are questioned by other scientists
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