evolution chapter 9 terms Flashcards
gene flow
net movement of alleles from one population to another
non-random mating
occurs when individuals select mates based on particular phenotypes or due to interbreeding
genetic drift
changes in allele frequency due to chance events
founder effect
few individuals start and establish a new, isolated population
ex: galapagos islands
bottleneck effect
change in gene pool resulting from rapid decrease in population size
ex: elephant seals (due to overhunting)
stabilizing selection
favours intermediate phenotypes and acts against extreme phenotypes
- results in narrower phenotype range
ex: babies birth weight
directional selection
favours phenotypes at one extreme over another
- results in shifted range
ex: peppered moths
disruptive selection
favours both extremes rather than intermediate phenotypes
- results in split gene pool
ex: salmon size differences
sexual selection
competition between males and choices made by females
sexual dimorphism
difference in phenotypes of male and female
ex: colours (bright vs. dull)
balanced polymorphism
selection can favour 2 or more alleles for same trait in steady proportions
ex: sickle cell anemia
speciation
formation of new species from existing species; a continuous process
pre-zygotic
pre-fertilization barriers
- prevents fertilization of eggs
post-zygotic
barriers after fertilization
- prevent hybrid zygotes from developing into fertile, viable offspring
sympatric speciation
populations within same geographical area diverge genetically
ex: polyploidy- results in extra chromosomes due to error in cell division
allopatric speciation
populations separated by a geographical barrier and diverge genetically
ex: lava flow, water
adaptive radiation
diversification of a common ancestral species into a variety of differently adapted species
ex: galapagos islands
ecological niche
increase in number of species, sharp declines in number of species
divergent evolution
occurs when populations adapt to different environmental conditions, diverge and become distinct
- common ancestor
ex: adaptive radiation
convergent evolution
occurs when unrelated species occupy similar environments in different parts of the world
- no common ancestor
ex: birds and bats have wings
gradualism
small, adaptive changes gradually accumulate over time
- fossils rarely reveal gradual transition
punctuated equilibrium
interrupted by periods of divergence
- supported by fossil evidence
