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Biology Vocab and Key Concepts for Chapter 16 Evolution of Populations


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gene pool
combined genetic information of all the members of a particular population
relative frequency
the number of times that allele occurs in a gene pool compared with the number of times other alleles occur
single-gene trait
controlled by a single gene that has two alleles
polygenic trait
often has two or more alleles
What two processes can lead to inherited variation in populations?
the two main sources of genetic variation are mutaitons and the genetic shuffling that results from sexual reproduction
How does the range of phenotypes differ between single-gene traits and polygenic traits?
The number of phenotypes produced for a given trait depends on how many genes control the trait.
directional selection
individuals at one end of the curve have higher fitness than individuals in the middle or other end; evolution causes an increase in the number of individuals with the trait at one end of the curve
stabilizing selection
the curve have higher fitness than individuals at either end of the curve; keeps center of curve same but narrows overall graph
disruptive selection
individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle; selection creates two distinct phenotypes
genetic drift
random change in allele frequency
founder effect
situation in which allele frequencies change as a result of the migration of a small subgroup of a population
Hardy-Weinberg principle
states allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change
genetic equilibrium
allele frequencies remain constant; if no change then they don't evolve
describe how natural selection can affect traits controlled by single genes.
natural selection on single-gene traits can lead to changes in allele frequencies and thus to evolution
describe three patterns of natural selection on polygenic traits. which one leads to two distinct phenotypes?
natural selection can affect the distributions of phenotypes in any of three ways: directional selection, stabilizing selection, or disruptive selection. disruptive selection
how does genetic drift lead to a change in a population's gene pool?
in small populations, individuals that carry a particular allele may leave more descendants than other individuals, just by chance. over time, a series of chance occurrences of this type can cause an allele to become common in a population
what is the Hardy-Weinberg principle?
Five conditions are required to maintain genetic equilibrium from generation to generation:
-there must be random mating; -the population must be very large;
-and there can be no movement into or out of the population, -no mutations,
-no natural selection
formation of new species
reproductive isolation
when the members of two populations cannot interbreed and produce fertile offspring
behavioral isolation
when two populations are capable of interbreeding but have differences in courtship rituals or other types of behavior
geographic isolation
two populations are separated by geographic barriers such as rivers, mountains or bodies of water
temporal isolation
two or more species reproduce at different times
how is reproductive isolation related to the formation of new species?
as new species evolve, populations become reproductively isolated from each other
what type of isolating mechanism was important in the formation of different Galapagos finch species?
speciation in the Galapagos finches occurred by founding of a new population, geographic isolation, changes in the new population's gene pool, reproductive isolation and ecological competition.

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