Presentation on theme: "What is Evolution? Produces biological diversity - DNA sequence variation - Bacteria - Flowering plants - Sexual selection in birds - Human civilization."— Presentation transcript:
What is Evolution? Produces biological diversity - DNA sequence variation - Bacteria - Flowering plants - Sexual selection in birds - Human civilization Evolutionary Genetics: mechanisms Science: understanding; predictions
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”
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 What causes evolution?
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: > 95% of genome maybe "junk"!) However, many interesting types of evolution involve natural selection
Evolution, a fact? You don’t 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 it’s 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.
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)
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
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
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!
A flow diagram for Random mating Offspring genotypes in Hardy-Weinberg ratios Offspring after selection Natural selection So now you can write an evolution computer program! Numerical vs. analytical theory
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 (W=1-s) and predict rates of evolution from data on survival or fecundity. Mathematical theory makes evolution a predictive science
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