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Lec 14 BioLec Notes.docx

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Western University
Biology 1001A
Tom Haffie

Lec 14 BioLec Notes Selection on Quantitative Traits Stabilizing, Directional, Disruptive Stabalizing selection is the most common type Directional selection is the next most common type, individuals in one end of the distribution have high fitness relative to every body elese Why hasn’t directional selection already removed all genetic variation for traits relate to fitness? - Vast majoiryt of natural population has huge amount of genetic variation Selction has not removed all these deleterious alleles? - Sudden change in environment, so in cases environment changes, direction of selection changes, so the negative in Selection pressures are not uniform over time, or over space Selection pressure varies over time, and across habitats - A phenotype that has a selective advantage in one part of habitiat might not have a selective advantage in another part of habitiat Pale colour morph and White color Morph In unpolluted environment, pale colour moth was very criptic that enable protection from predators Dark color moths has low fitness When trees were colored in soot no longer for pale for to hide in bark and then the dark colored was advantageous Adaptations (traits that increase bearer’s relative fitness) are environment-specific Disruptive Selection - involves selective advantage on either extreme - The mean value of the trait may not change - Examples: Birds in Galapagos islands… There was a drought.. individuals with small bills have high fitness, individuals have large bills have high fitness too… Individuals with medium bills are disadvantage during a drought - If birds will big bills only breed with big bills birds, the medium individuals might completely disappear Frequnecy-dependent selection Selection and the adatpative calue of the relative phenotype has to do with If it’s the most common form of allele in the population hten it will Pos
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