Natural Selection II Flashcards
What are the three general forms of selection?
Directional selection
Stabilizing selection
Diversifying selection
What is another name for directional selection?
Positive selection
What is another name for stabilizing selection?
Purifying/negative selection
What is another name for diversifying selection?
Divergent selection
What is directional selection?
a. Selection that causes directional changes in the evolution of a trait
What is stabilizing selection?
a. Selection that prevents changes to a trait by selecting against variants that deviate from the optimal trait
What is diversifying selection?
a. Selection that causes a population to diverge in two directions
What type of selection is shown in this graph?
Directional selection
What type of selection is depicted in this graph?
Stabilizing selection
What type of selection is depicted in this graph?
Divergent selection
What is the Breeder’s equation?
Predicts the response to selection over a single generation
What is this equation? Define all variables
Breeders equation
z1 = mean trait value of offspring
z0 = mean parental value
h^2 = heritability
S = selection differential
What is this equation? Define all variables
Breeder’s equation with selection gradient
Vg = genetic variance
Beta = selection gradient
What are phenotypic selection analyses?
Estimates natural selection according to the covariation between relative fitness and traits among individuals.
What are genotypic selection analyses?
Estimates natural selection according to the covariation between relative fitness and traits among genotypes or genetic families.
Define adaptive traits.
Adaptive traits increase the ability of an individual to survive or reproduce compared with individuals without the trait.
By definition, what does evolution by natural selection lead to?
Evolution of adaptations
What are the 4 misconceptions of evolution?
Populations evolve to future environments
Adaptive evolution is progressive, leading to the evolution of better and more complex forms
Adaptations evolve by random chance
Evolution cannot lead to complex organs.
Correct this misconception: Populations evolve to future environments
o Evolution by natural selection is never forward looking, it is a function of past selection/environments
o Changes in environment might render species maladapted
o Don’t know what’s coming, only respond to what is happening
Correct this misconception: Adaptive evolution is progressive, leading to the evolution of better and more complex forms
o Adaptation is not necessarily progressing to better and more complex forms. Populations adapt to previous environmental conditions
o Evolution by natural selection can lead to more complex OR simpler forms, depending on which traits are most fit and given adequate genetic variation
Give examples of evolution leading to simpler forms.
Loss of eye function
Tapeworms losing digestive capacity
Loss of photosynthesis in some plants (parasitic)
Correct this misconception: Adaptations evolve by random chance
o Mutations are more or less random
o Natural selection is anything but random – it is the antithesis of random
o Natural selection leads to a near inevitable increase of the “best” (fittest) strategy within a population
Correct this misconception: Evolution cannot lead to complex organs
o If intermediate steps increase fitness, then natural selection can lead to the evolution of complex adaptive traits.
