Patterns and Result of Selection Flashcards
natural selection can…
change trait value over time in different patterns due to fitness
stabilizing selection
favors the trait mean (which stays the same)
individuals at either extreme have a lower fitness
decreases phenotypic/genotypic variation
directional selection
favors one trait extreme - decreases variation
if directional selection operates over many generations, an evolutionary trend occurs
a particular allele may be favored if it is the adaptive version of a trait
disruptive selection
favors two trait extremes
individuals at either extreme are more successful than the average
ways selection can be maintained
frequency-dependent selection
heterozygote advantage
clinal variation
frequency-dependent selection
often favors the less-common trait, which makes it become more common, which makes it less common in turn
ex: left-mouth and right mouth fish
heterozygote advantage
often appears in a variable advantage
ex: butterfly flight
one PGI allele favors flight in hot conditions while the other favors in cold conditions
heterozygotes can fly over a larger temperature range
clinal variation
- observed in populations that occupy a large area
- genetic variation is maintained in populations in different geographic regions as selective pressures tend to change through space
ex: white clover plants
trade-off
- traits that are adaptive in one context may not be in another
- ex: roughed skinned newts + TTX resistant snakes
convergent evolution
makes similar shapes from different starting materials
ex: fishes’ developmental capacities constrain the pathway that evolution can take
evolutionary constraint
- new traits are derived from old ones and retain evidence of their origin
- selection can only act on variation that already exists
- evolution only changes allele frequency, not their origin
- traits and features are modifications of existing structures
