Download So…….what is natural Selection?

Natural Selection
Garielle Wagnac
Who knows?
Natural Selection………
• It’s a process
– 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
I. Allele variation due to mutation (may
alter function of protein)
II. Some alleles enhance reproductive
success
III. Beneficial alleles more likely to survive
IV. 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
There are 4!
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…….
Balancing Selection
Heterozygote Advantage
• Phenomenon where
heterozygotes have a
higher fitness than the
corresponding
homozygotes
Negative frequencydependent selection
• Fitness of a genotype
decreases when its
frequency becomes
higher!
At least, I hope so!
NOW YOU KNOW EVERYTHING
ABOUT NATURAL SELECTION!