Lecture: #3 (Darwin's Dangerous Idea) Flashcards
Evolution
A change in allele frequencies within a population [over time]
[4 types (Evolutionary agents): Natural Selection, Mutation, Gene Flow (Migration), Genetic Drift]
Allele
one variant of a gene (several may exist)
[“Alternative versions of a gene.”]
Gene
Section of DNA instructing how to produce a trait
[“The basic unit of heredity; a sequence of DNA nucleotides on a chromosome that carries the information necessary for making a functional product, usually a protein or an RNA molecule.”]
Natural selection
Non-random elimination of trait/alleles/genotypes in a population over time
[requires: Variation, Heritable, Differential Reproductive Success]
[Mechanism of evolution]
(ex. evolving long necks has enabled giraffes to feed on leaves that others can’t reach, giving them a competitive advantage. Thanks to a better food source, those with longer necks were able to survive to reproduce and so pass on the characteristic to the succeeding generation.
Directional selection
Selection that, for a given trait, increases fitness at one extreme of the phenotype and reduces fitness at the other
[NS: reproductive success]
[ex. selective breeding by dairy farmers of cows with high milk production, results in a shift in the average milk production over generations ]
Stabilizing selection
Selection that, for a given trait, produces the greatest fitness at the intermediate point of the phenotypic range
[NS: reproductive success]
[ex. the average birth weight of the population is 7 pounds because extremely heavy or very low birth weight babies often face challenges and may not survive]
Disruptive selection
Selection that, for a given trait, increases fitness at both extremes of the phenotype distribution and reduces fitness at middle values
[NS: reproductive success]
[ex. Salmon compete to fertilize eggs. Larger males have an advantage in territory battles and smaller fully mature males can still succeed by quickly fertilizing eggs.] [or different beak shapes/sizes]
