Hardy-Weinberg & Pop Genetics
The movement of alleles between populations through migration and interbreeding.
What is gene flow?
Selection that shifts a population's phenotypes toward one extreme, as when dark peppered moths became common near sooty industrial cities.
What is directional selection?
Speciation that occurs when a physical barrier, such as a mountain range or river, splits a population.
What is allopatric speciation?
Structures that share a common evolutionary origin even when their functions differ, like a bat wing and a human arm.
What are homologous structures?
When a small group of colonists starts a new population, its allele frequencies can differ from the source population; this is called this effect.
What is the founder effect?
Selection that favors intermediate phenotypes and removes both extremes, as with human birth weight.
What is stabilizing selection?
Speciation without geographic separation, often through polyploidy in plants.
What is sympatric speciation?
Structures with similar functions but separate evolutionary origins, like bird wings and insect wings, result from this process.
What are analogous structures (convergent evolution)?
A sudden, drastic reduction in population size that sharply cuts genetic variation, as seen in cheetahs and northern elephant seals.
What is a population bottleneck?
Selection that favors both extreme phenotypes over the intermediate, as in birds with very large or very small beaks and few medium ones.
What is disruptive selection?
This prezygotic barrier keeps species apart because they breed at different times of day or year.
What is temporal isolation?
Reduced or nonfunctional remnants of structures that were useful in ancestors, such as the pelvic bones in whales.
What are vestigial structures?
The ultimate source of all new alleles, including point changes, insertions, deletions and duplications.
What is mutation?
When heterozygotes have higher fitness than either homozygote, both alleles are maintained, as with sickle-cell and malaria.
What is heterozygote advantage (a form of balancing selection)?
In this postzygotic barrier, hybrids such as mules survive to adulthood but are sterile.
What is reduced hybrid fertility (hybrid sterility)?
A group that includes a common ancestor and ALL of its descendants is described by this term, also called a clade.
What is a monophyletic group?
To stay in Hardy-Weinberg equilibrium, a population must meet five conditions; name any four of them.
What are no mutation, no gene flow, random mating, a very large population (no genetic drift), and no natural selection?
In this form of nonrandom mating, individuals mate with relatives, raising homozygosity without changing allele frequencies.
What is inbreeding?
In this selection, a phenotype's fitness depends on how common it is, as in scale-eating fish whose rarer mouth direction gains an edge.
What is negative frequency-dependent selection?
Rapid diversification of one ancestral lineage into many ecologically different species, as with Darwin's finches.
What is adaptive radiation?
A shared derived character that is present in a clade's members but absent from earlier ancestors is known by this term.
What is a synapomorphy?