Ch. 23: The Evolution of Populations
intersexual selection
(mate choice) individuals of one sex are picky in selecting mates (females to males)
Cline
Geographic distribution may be shown in a graded manner along a geographic axis known as a _______
crossing over, independent assortment, fertilization
Much of the genetic variation that makes evolution possible comes through sexual reproduction. What are the three mechanisms by which sexual reproduction shuffles existing alleles?
mutation
Several sources of genetic variation are available. What is the ultimate source of new alleles?
whole-gene level or molecular level
Using techniques of molecular biology, what are the two ways of measuring genetic variation in a population?
natural selection
What is the only mechanism that is adaptive, or improves the match between organisms and their environment?
sexual dimorphism
What is the result of sexual selection?
microevolution
a change in allele frequencies in a population over generations
sexual dimorphism
a difference between the two sexes in secondary sexual characteristics
stabilizing
acts against extreme phenotypes; favors intermediate varieties
gene pool
all copies of every type of allele at every locus in all members of the population
fixed allele
all individuals are homozygous
natural selection
by favoring some alleles over others, _____ can cause adaptation
Genetic drift
chance events can cause allele frequencies to fluctuate unpredictably
discrete characters
determined by a single gene
gene duplication
due to errors in mitosis; slippage during DNA replication, or the activities of transposable elements
diploidy; heterozygote advantage
explain two ways in which genetic variation is preserved in a population?
founder effect
genetic drift that occurs when a few individuals become isolated from a larger population and form a new population whose gene pool composition is not reflective of the original population
bottleneck effect
genetic drift that occurs when the size of the population is reduced, as by natural disaster or human actions. Survivors are not representative of the original population
population
group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
gene variability = 0; # of alleles = 1
if the nucleotide variability of a locus = 0%, what is the gene variability and # of alleles at that locus?
heterozygote advantage
maintenance of two alleles because heterozygote individuals are more fit
directional
occurs when conditions favor individuals exhibiting one extreme
disruptive
occurs when conditions favor individuals from both extremes over intermediate
gene flow
of the three factors tends to reduce the genetic differences between populations and make populations more similar?
natural selection
of the three factors you previously listed, only one results in individuals that are better suited to their environment. Which is it?
diploidy
recessive alleles are hidden and not expressed; thus even fatal alleles stay in the gene pool
intrasexual selection
selection within the same sex, individuals of one sex compete directly for mates of the opposite sex
stabilizing selection
sparrows with average sized wings survive severe storms better
relative fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals
Hardy-Weinberg principle
the frequencies of alleles and genotypes will remain constant in a population from gen. to gen. provided that only Mendelian segregation and recombination of alleles are at work
Gene flow
the transfer of alleles into or out of a population due to the movements of fertile individuals or their gametes
quantative characters
vary along a continuum within a population, results from the influence of 2 traits
natural selection, genetic drift, gene flow
what are the three main mechanisms that can cause changes in allele frequencies?
genetic drift
which of the previous factors results in a random, nonadaptive change in allelic frequencies?