Lecture 8- Evolutionary Mechanisms Flashcards
polygenic inheritance
multiple genes independently affect a single character (Ex. Height)
Pleiotropy
the ability of a single gene to have multiple effects
Genetic drift
chance events cause allele frequencies to fluctuate unpredictably
genetic drift is caused by
chance events associated with survival and reproduction
in genetic drift, the smaller the sample:
the greater the chance of random deviation from a predicted result
difference between natural selection and genetic drift is
natural selection is based on optimal phenotypes and evolution is carried out based on that while genetic drift is random
can genetic drift be predicted?
no, it’s random
founder effect
when a few individuals become isolated from the larger population, the new population’s gene pool will differ from the source population
Bottleneck effect
sudden change in the environment drastically reduces the size of the population
Are bottleneck effect and founder effect examples of genetic drift?
no, but they can RESULT in genetic drift
Genetic drift can limit the ability of a population to
adapt
adaptation definition
a feature that arose and was favored by natural selection for its current function
Gene flow
the movement of alleles among populations
alleles can be transferred through the movement of
fertile individuals or gametes
gene flow tends to reduce
variation among populations over time
Gene flow can also increase a population’s
fitness
What is the only mechanism that consistently causes adaptive evolution
natural selection
Adaptive evolution
traits that enhance survival or reproduction tend to increase in frequency over time.
The ways natural selection can alter the frequency distribution of heritable traits
directional selection
disruptive selection
stabilizing selection
Directional selection
conditions favor individuals at one extreme of a phenotypic range
disruptive selection
conditions favor individuals at both extremes of the phenotypic range over the intermediate phenotypes
stabilizing selection
conditions favor intermediate phenotypes over both extremes