Unit 7: Chapter 23 Flashcards
natural selection acts on ______, whereas only ______ evolve
individuals
populations
population genetics
the study of how populations change genetically over time
population
localized group of individuals capable of interbreeding and producing fertile offspring
gene pool
all of the genes in a population at any one time
hardy Weinberg theorem use
used as a benchmark to measure evolution against
the hardy Weinberg theorem states that frequencies of alleles and genotypes in a population’s gene pool ________
remain constant from generation to generation
five conditions for hardy Weinberg equilibrium
large population no gene flow no mutations random mating no natural selection
p
frequency of the dominant allele
q
frequency of the recessive allele
p^2
percent of individuals with the homozygous dominant genotype
q^2
percent of individuals with the homozygous recessive genotype
2pq
percent of individuals with the heterozygous genotype
the two hardy Weinberg equations
p + q = 1
p^2 + 2pq + q^2 = 1
mutations
changes in the nucleotide sequence of DNA that cause new genes and alleles to arise
point mutation
change of one base in a gene
usually harmless
can have a significant impact on phenotype
______ and ______ produce the variation that makes evolution possible
mutations and sexual recombination
three major factors the alter allele frequencies and bring about the most evolutionary change
natural selection
genetic drift
gene flow
genetic drift
describes how allele frequencies fluctuate unpredictably from one generation to the next
tends to reduce genetic variation trough a loss of alleles
the smaller the sample, the greater chance of deviation from a predicted result
genetic drift: bottleneck effect
sudden change in the environment that may drastically reduce the size of a population
resulting gene pool may no longer resemble the original population’s gene pool
genetic drift: founder effect
a few individuals become isolated from a larger population
can affect allele frequencies in the population
gene flow
genetic additions or subtractions from a population resulting from the movement of fertile individuals or gametes
causes a population to gain or lose alleles
tends to reduce differences between populations
discrete characters
variation that can be classified on an either-or basis
punk or white or red flowers
quantitative characters
variations that vary along a continuum within a population
race
IQ
phenotypic polymorphism
a population in which two or more distinct forms of a character are represented phenotypically
discrete characters
genetic polymorphisms
heritable components of characters that occur along a continuum in a population
quantitative characters
geographic variation
a difference between gene pools of separate populations
fitness
the contribution an individual makes to the gene pool of the next generation compared to the contributions of other individuals
relative fitness
the contribution of a genotype to the next generation compared with the contributions of other genotypes
directional selection
favors individuals at one end of the phenotypic range
only shades of dark fur OR only shades of light fur
disruptive selection
favors individuals at both extremes of the phenotypic range
only very light fur AND very dark fur
stabilizing selection
favors intermediate variation and acts against extreme phenotypes
medium colored fur
diploidy
maintains genetic variation in the form of hidden recessive alleles that can appear again
balancing selection
when natural selection maintains stable frequencies of two or more phenotypic forms in a population
also called balanced polymorphism
heterozygous advantage
some heterozygous individuals have a greater fitness than homozygous individuals
this maintains the passing on of both the dominant and recessive alleles
sexual selection
natural selection for mating success
can result in sexual dimorphism
sexual dimorphism
differences between sexes in secondary sexual characteristics
INTRAsexual selection
direct competition amongst individuals of one sex for mating rights to the other
INTERsexual selection
also called mate choice
individuals of one sex (usually females) are picky in selecting their mates from the other sex
microevolution
change in the genetic makeup of a population from generation to generation
