BI111 Lecture Notes - Lecture 10: Selective Breeding, Adaptive Radiation, Allele Frequency

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1 Feb 2017
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BI111- Lecture 10 January 25th, 2017- Why are there so many species?
Changes in Allele Frequencies Over Time
Evolution encompasses all types of changes brought about by selection processes and
chance events
Charles Darwin suggested mechanism of adaptive evolution (natural selection), and used
domesticated species to first illustrate concept of artificial selection: change associated
with exaggeration of desirable (from human perspective-Losers are the better chance of
higher reproduction) rather than improved survival or reproductive abilities (Increased
fitness)
Naturalist working around the 1800’s, he didn’t have DNA to talk about so instead he
was giving the example that the public would understand (analogous reproduction was
artificial selection)
Domesticated Species and Adaptation
Depending on environment, different phenotypes are adaptive or deleterious
Traits (with genetic basis) that might otherwise put individuals at a competitive
disadvantage may be desirable to humans and thus become favoured by selective
breeding
Adaptive trait gives freedoms to babies to have their own freedom and not be reliant on
their parent
Selection has changed allele frequencies over time
E.g. Change from dehiscence (shed ripened grains) to indehiscence (hold on to ripened
grains)
Darwin’s Pigeons
Artificial Selection is an analogous process to Natural Selection
Pigeon breeding was hugs in the 1800’s
Co-lineages that result in unique patterns (Selective disadvantage such as long feathers on
their feet, but they are domesticated species so they are reproduced
Persistent human selection on pug lineages has led to the uprising of pugs we see today
(No longer resemble ancestors and won’t do well in nature)
Darwin’s Finches
Adaptive Radiation driven by divergent selection on sub-populations to utilize alternate
food resources
Finches began specialized to exploit certain food sources (Which changes beak thickness
and length)
Differences become so great that they are distinct species (The product of selection and
beneficial in the present)
Selection acts on the phenotype at the individual level, but adaptive evolutionary change
is manifested at the population level
Changes in the finches’ beaks occurred by chance, and when there was a good match
between beak structure and available food, those birds had more offspring (It is not goal
oriented)
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