Natural Selection Garielle Wagnac

So…….what is natural Selection? Who knows?

Natural Selection……… It’s a process Causes evolution to occur Beneficial traits inherited become more common in consecutive generations Causes evolution to occur Happens because of adaptation

Yes, Natural Selection favors individuals! BUT WHICH?!?!

Reproductive Success Likelihood of an individual contributing fertile offspring to the next generation Traits favorable to reproductive success Two categories of traits Characteristics organisms better adapted Traits associated with reproductive success

Principles of Natural Selection Allele variation due to mutation (may alter function of protein) Some alleles enhance reproductive success Beneficial alleles more likely to survive Allele frequency change through natural selection

How do you measure reproductive success? FITNESS likelihood that a genotype will contribute to gene pool of next generation compared to other genotypes Mean Fitness average reproduction success of members *as mean increases, so does natural selection of organisms

AA produces 5 offspring Aa produces 4 offspring aa produces 1 offspring

Natural Selection Paths There are 4! Natural Selection Paths

Directional Selection Individuals at one extreme of phenotypic range have greater reproductive success in a particular environment Arise from? New allele added Expose to change in environment

Stabilizing Selection Favors individuals with intermediate phenotypes an selects against those with extreme phenotypes Tends to decrease genetic diversity

Diversifying (Disruptive) Selection Favors the survival of two or more different genotypes that produce different phenotypes Likely to occur in populations that occupy heterogeneous environments

Balancing Selection Type of natural selection that maintains genetic diversity Balanced polymorphism occurs 2+ alleles kept in balance of each other Can happen by…….

Negative frequency-dependent selection Heterozygote Advantage Balancing Selection Negative frequency-dependent selection Heterozygote Advantage Phenomenon where heterozygotes have a higher fitness than the corresponding homozygotes Fitness of a genotype decreases when its frequency becomes higher!

NOW YOU KNOW EVERYTHING ABOUT NATURAL SELECTION! At least, I hope so! NOW YOU KNOW EVERYTHING ABOUT NATURAL SELECTION!