BIOL 2300 Lecture Notes - Lecture 3: Allele Frequency, Allopatric Speciation, Species Problem
22 Jun 2018
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LECTURE 3 EVOLUTION 2
Evolution
Three General Types of Selection
Evidence of Natural Selection in Nature?
Does exploitation cause evolution?
Commercial Fishing
In the wild:
Evolution can result in new species…
How does speciation occur?
E.g. Cichlids - Nicaragua
What maintains speciation?
Summary - Quiz
2
Evolution
• Evolution is a change in the genetic composition of a population of a species
over time.
• Hardy-Weinberg Principle: the genetic composition (allele frequencies)
within a population does not change (~evolution does not occur) unless one of
the following things occur:
1. Mutations – can create an allele
o Very small changes add up across generation
2. Non-random mating among individuals in a population (certain individuals
more desirable)
o E.g. blonde individuals only mate with other blondes
o If random mating – allele frequencies will stay the same
3. Random variations in fecundity/mortality
o Can eliminate an allele from a population
4. Natural selection – most important!
o Selective pressures (or changing abiotic and biotic factors) → varying
fitness among individuals → favourable traits are passed on to future
generations at a higher frequency → genetic composition of the
population changes over time
o Evolving to match the environment
Document Summary
Evidence of natural selection in nature: eg. In industrialized areas: soot deposited on tree trunks, dark colour more favourable, genetic composition of population changed over generations. In the wild: fishing pressure can significantly change the genetic composition of populations in 20-50 yrs, size-selection is one of the primary reasons why overexploited fish populations do not recover. Evolution can result in new species : biological species concept: distinguish species based on their potential to interbreed and produce fertile offspring. Implies that reproductive isolation (or genetic isolation) defines a species because reproduction is the means of transferring genetic information (dna) 2nd: isolated subpopulation experiences different selection pressures ( different favourable traits varying fitness) 3rd: genetic composition of subpopulation changes over generations (1 via natural selection) 4th: after generations, if the isolated subpopulation can no longer interbreed with the origin population speciation. Cichlids - nicaragua: example of sympatric speciation, small, isolated, low productivity lakes, midas & arrow cichlid species.
