What%20is%20Evolution?

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What is Evolution?

• Produces biological diversity
• - DNA sequence variation
• - Bacteria
• - Flowering plants
• - Sexual selection in birds
• - Human civilization
• Evolutionary Genetics mechanisms
• Science understanding predictions

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Evolution definition

• Darwin "descent with modification
• A change in morphology, ecology, behaviour,
  physiology
• Change must be genetic
• Modern, genetic definition
• evolution is change in gene frequencies
  between generations

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What causes evolution?
a) Natural selection b) Mutation c) Genetic
drift, or neutral, random evolution e)
Migration, or gene flow This lecture simple
examples of evolution by natural selection
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What is natural selection?

• a consistent bias in survival or fertility
  between genotypes within generations
• Selection often causes evolution, but may also
  prevent evolution (e.g. stable polymorphism)
• Evolution does not require selection (e.g. drift
  -- important gt 95 of genome maybe "junk"!)
• However, many interesting types of evolution
  involve natural selection

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Evolution, a fact?

• You dont have to believe in evolution to take
  this course, but you do have to know the
  arguments to get a good grade!
• Evolution is a fact, and its hard to ignore
• but, theory and fact not so different
• Science prediction
• According to Karl Popper science is falsifiable.
  Falsehoods disprovable truth more difficult!
• Religion truth is by faith. Very different.

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Selection and the single gene

• Quantitative traits (e.g. size, behaviour)
• usually multiple loci
• Single-locus traits
• great examples of evolution by natural
  selection
• Many single-locus traits are involved in
• resistance to stress (often humans)

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Examples of single-gene traits

• Industrial melanism in moths (resistance to urban
  pollution)
• Heavy metal tolerance in plants growing in mine
  tailings
• Malaria resistance in humans (sickle-cell
  haemoglobin, etc.)
• Pesticide resistance (mosquitoes, insects, weeds,
  fungi, warfarin resistance in rats)
• Antibiotic resistance in bacteria
• We used to do this for tutorial there are many
  references on reserve, still see eUCLid

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The peppered moth Biston betularia
Left form typica (left, and carbonaria (right)
on lichen-covered trunk in Dorset. Right on
soot-covered tree near Birmingham
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How does evolution by natural selection work?

• Evolution by natural selection is an inevitable,
  mathematical process.
• The frequency of a particular allele will change,
  and its rate of change will depend mathematically
  on the advantage (or relative fitness) of that
  allele.
• Mathematical evolutionary theory is useful. For
  example, given information about natural
  selection, how rapidly will evolution occur?
• The answers help us understand antibiotic
  resistance, or pest resistance, for instance.
• Evolution is a predictive science! Useful, as
  well as fun!

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A flow diagram for
Random mating
Offspring genotypes in Hardy-Weinberg ratios
Natural selection
Offspring after selection
So now you can write an evolution computer
program!
Numerical vs. analytical theory
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Take-home points

• Evolution to a geneticist a change in gene
  frequencies.
• Natural selection a consistent bias favouring
  some genotypes over others.
• Evolution can occur in the absence of natural
  selection,
  via genetic drift or neutral evolution.
• Natural selection can stabilize the status quo
  zero evolution.
• Evolution at a single dominant gene rate can be
  predicted
• If selected, dominant alleles evolve quickly when
  rare, slowly when common recessive alleles
  evolve slowly when rare, quickly when common.
• We can estimate selection coefficients (s),
  fitnesses (W1-s) and
  predict rates of evolution from data on survival
  or fecundity.
• Mathematical theory makes evolution a predictive
  science

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Further reading

• FUTUYMA, DJ 1998. Evolutionary Biology. Chapters
  12 and 13 (pp. 371-381).
• References on natural selection at single genes
  for resistance (see web)
• Science Lbrary View B242 Teaching Collection by
  going to eUCLid use Keyword, Basic Search, All
  Fields B242