UCSB EEMB 2 - Lec #13 EEMB 2 SM17 1S (Selection) (15 pages)

Previewing pages 1, 2, 3, 4, 5 of 15 page document View the full content.
View Full Document

Lec #13 EEMB 2 SM17 1S (Selection)



Previewing pages 1, 2, 3, 4, 5 of actual document.

View the full content.
View Full Document
View Full Document

Lec #13 EEMB 2 SM17 1S (Selection)

56 views


Pages:
15
School:
University of California, Santa Barbara
Course:
Eemb 2 - Introductory Biology III

Unformatted text preview:

Natural Selection The evolutionary process A blend of chance and sorting 1 Variation Variation 2 Natural selection 3 Genetic Divergence 4 Reproductive Isolation Natural Reproductive Genetic isolation Selection Divergence 5 Speciation Speciation Natural Selection From the range of available variations natural selection increases the frequencies of certain genotypes that confer reproductive success fitness Organisms are fit when adapted to their environment Natural Selection Evolutionary fitness The contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals Ex Wildflowers Variants color shape fragrance differ in reproductive success variants have adaptive advantages Relative fitness The contribution of a genotype to the next generation compared to the contribution of alternative genotypes for the same locus Ex Wildflowers red flower AA variants produce 5 offspring pink flower Aa variants produce 4 offspring and white flower aa variants produce 1 offspring 1 Fitness of AA WAA 1 0 highest reproductive success set to 1 2 Fitness of Aa WAa 4 5 0 8 3 Fitness of aa Waa 1 5 0 2 Natural Selection Natural selection acts on phenotypes not genotypes The relative fitness of an allele depends on the entire genetic and environmental context in which it is expressed Reproductive success Survival and Fecundity 1 Survival does not guarantee reproductive success 2 Organisms must be fecund fertile producing viable offspring Must survive and be fecund to be fit Mean fitness of population The average reproductive success Continuous Variation greater contribution well adapted high fitness less contribution not well adapted low fitness of individuals of members of a population 0 X 50 Measured trait 100 Natural Selection Types of Natural selection 1 Stabilizing Selection Intermediate forms of traits are favored and alleles that specify extreme forms are selected against reduces variation by counteracting effects of sexual recombination mutation and migration Favors the survival and reproduction of the intermediate phenotype phenotypic character Basic conditions 1 environment remains stable over time 2 organisms have obtained a high state of adaptiveness Natural Selection 0 X 50 Measured trait X time long of individuals of individuals Stabilizing Selection 0 100 50 Measured trait 100 Individuals that are well adapted cluster around the mean Ex Human birth weight of individuals low or high weight leads to high mortality X 6 6 lbs 8 8 lbs Measured trait Natural Selection 2 Directional Selection Favors survival and reproduction of phenotypes at one extreme or the other of phenotypic distribution Allele frequencies in a range of phenotypic characteristics shift in one direction or another Individuals that deviate from the average are favored occur when mutations appear and prove adaptive Basic conditions 1 Environmental and or biological conditions are changing over time 2 Species can not be completely adapted to



View Full Document

Access the best Study Guides, Lecture Notes and Practice Exams

Loading Unlocking...
Login

Join to view Lec #13 EEMB 2 SM17 1S (Selection) and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lec #13 EEMB 2 SM17 1S (Selection) and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?