Lecture 5: Evolution & Intro to Plasticity Flashcards
Evolution definitions
- descent w/ modification & often diversification (macro)
- change in allele frequency in population (micro)
- change in the inherited traits of a population of organisms through successive generations
Forces that change allele frequencies in populations
- mutation - random (ultimate source of genetic variation)
- selection - adaptive
- genetic drift - random
- gene flow - emigration/immigration
Evolution by natural selection
Acts on phenotypes –> changes allele frequencies
Ingredients:
* Variability in phenotypic trait
* Differential fitness
* Heritability
Selection differential
traint mean of original population vs. surviving parents
Types of phenotypic shifts
- Directional
- Stabilizing (extreme @ adv/disadv)
- Disruptive (not intermediate)
Genetic drift
- smaller # of offspring –> greater possible change in gene frequencies
- lower allele frequency in parents –> greater chance of loss
Drift randomly reduces genetic variability –> more prominent in small pop
Inbreeding depressions (small populations)
Reduced fitness (result of mating –> expression of deletrious recessive alleles)
Gene flow
Reinforces/opposes changes that occur via natural selection/drift
* net movement of particular alleles to/from population
* if movement not random –> gene flow occurs
Adaptive evolution relies on…
Chance events (mutations & recombination) & non-random process of selection
Constraints on adaptation
- requires standing genetic variation
- fitness is relative
- adaptive traits may trade-off w/ each other
- selection pressure is variable
- can take a long time, even if environments constantly change
Phenotypic plasticity
ability of the same genotype to produce different phenotypes in response to variation in the environment
Reaction norm
shows relationship between phenotype & environmental conditions for given genotype when phenotype is continous
