BIO 185 Lecture 5: Lecture 5

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20 Jul 2016
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1. 5 - natural selection, sca case study, speciation. Directional selection: movement (shift) of one phenotype in one direction. Disruptive selection: gravitate towards the middle phenotype example: babies born at a middle birth weight favor the extreme phenotypes (not the middle) example: light & dark mice survive on light & dark rocks, medium-colored mice don"t survive. Do all selected traits increase survival? example: bright blue frog (might not be advantageous for survival: exaggerated often (seemingly) functionless traits, are predominantly in males sexual selection is the best explanation for exaggerated, sexually dimorphic traits. Natural selection: affects changes in frequency of alleles that in uence survival or fecundity. Sexual selection: affects changes is frequency of alleles that in uence mating success. Natural selection - process of adaptation to an environment. Hypothesis: there is something good (good advantage) of having sickled cells. Distribution of malaria/frequencies of the sickle-cell allele in africa are correlated.

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