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Lecture 10

BIOL215 Lecture 10 Notes.pdf

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McGill University
Biology (Sci)
BIOL 215
Neil Price

BIOL215 Lecture 10 Notes Overview on selection acts on populations in four ways: •Stabilizing selection •Directional selection •Disruptive selection •Sexual selection •Selection acts on variation •Selection constrained by genetic and developmental pathways. This means that not every single mutation that happens on the level of DNA or not every tinkering occurring in the environment shows up on the phenotype. If it did, it would be disastrous for the individual. Individuals have a way of buffering to protect themselves Is evolution survival of the fittest as discussed in class: •Survival of the most adaptable Coined by Herbert Spencer, was used by Wallace, and by Darwin in later editions of "The Origin of • Species" •Tautological- Darwin preferred "struggle for reproduction" •Natural selection is the umbrella term for a range of evolutionary processes, the outcome of which is differential survival and reproduction "Struggle for existence or survival of the fittest" is only one part of natural selection: •Biotic: being able to compete with your neighboring individuals in the same populations, individuals of a different species •Abiotic: being able to survive in your conditions Fitness: •The relative reproductive success of individuals, within a population, in leaving offspring for the next generation •Fitness of phenotype (individuals) vs genotype (alleles) •Need both survival and reproductive success Genotype vs. Phenotype Natural selection directly acts on the phenotype (what it looks like on the outside) • •Selection only indirectly affects the genotype Natural selection combined (view of Darwin for species we see today): •Vastness of geologic time •Uniformitarianism (gradual change in the environment) •Continuously limited resources •Non-random survival Stabilizing selection: when you are stabilize around the mean, when the mean is particularly well adapted to the environment and individuals on either side of the mean is selected out (i.e. optimal temperature for survival) Directional selection: when the mean is favored and shifted over to one direction with each passing generation (height in humans) Disruptive selection: when there are two peaks that are selected for; want two types of individuals in a particular population. It usually occurs when environments change very quickly Two ways to stabilize directional and disruptive selection: •Artificial selection: (Darwin used as a main source of evidence) the idea that breeder selects the parents deemed desirable and culls the undesirable types •Directional selection i
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