Chapter 21 Flashcards
quantitative variation
Variation that is measured on a continuum (such as height in human beings) rathe than in discrete units or categories
phenotypic variation
Differences in appearance or function between individual organsims
qualitative variation
Variation that exists in 2 or more discrete states with intermediate forms often being absent
polymorphism
The existence of discrete variants of a character among individuals in a population
“many” “form”
If a population of skunks includes some individuals with stripes and others with spots would you describe the variation as quantitative or qualitative?
The variation in skunks is qualitative
In the experiment on house mice, how did researchers demonstrate that variations in activity level had a genetic basis?
The researchers used artificial selection to change the activity levels of the mice
What factors contribute to phenotypic variation in a population?
Genetic variation, differing environmental effects on individuals, and interactions between genes and the environment affect phenotypic variation in a populaton
gene pool
The sum of all alleles at all gene loci in all individuals in a population
genotype frequencies
The percentage of individuals in a population possessing a particular genotype
allele frequencies
The abundance of one allele relative to others at he same gene locus in individuals of a population
null models
A conceptual model that predicts what one would see if a particular factor had no effect
Hardy-Weinberg principle
An evolutionary rule of thumb that specifies the conditions under which a population of diploid organisms achieves genetic equilibrium
genetic equilibrium
The point at which neither the allele frequencies nor the genotype frequencies in a population change in succeeding generations
What is the difference between the genotype frequencies and the allele frequencies in a population?
Genotype frequencies specify how alleles are combined in individuals, and allele frequencies specify how common the alleles are
Why is the Hardy-Weinberg principle considered a null model of evolution?
The Hardy-Weinberg principle is a null model because it identifies the conditions under which evolution will not occur
If the conditions of the Hardy-Weinberg principle are met, when will genotype frequencies stop changing?
If genotype frequencies are not already in equilibrium, they will stop changing after one generation of random mating
mutation
a spontaneous and heritable change in DNA; rare events
deleterious mutations
alter an individual’s structure function or behavior in harmful ways
lethal mutations
cause great harm to organisms carrying them
neutral mutations
neither harmful nor helpful
advantageous mutation
a change in DNA produces which confers some benefit on an individual that carries it
gene flow
The transfer of gene from one population to another through the movement of individuals or their gametes
genetic drift
Random fluctuations in allele frequencies as a result of chances events; usually reduces genetic variation in a population
population bottleneck
An evolutionary event that occurs when a stressful factor reduces population size greatly and eliminates some alleles from a population
founder effect
An evolutionary phenomenon in which a population that was established by just a few colonizing individuals has only a faction of the genetic diversity seen in the population from which it was derived
natural selection
the process by which such traits become more common in subsequent generations; the phenotype of an individual organism, rather than any particular allele
relative fitness
The number of surviving offspring that an individual produces compared with the number left by others in the population
directional selection
A type of selection in which individuals near one end of the phenotypic spectrum have the highest fitness
stabilizing selection
A type of natural selection in which individuals expressing intermediate phenotypes have the highest relative fitness
disruptive selection
A type of natural selection in which extreme phenotypes have higher relative fitness than intermediate phenotypes
sexual selection
A form of natural selection established by male competition for access to females and by the females’ choice of maters
sexual dimorphism
Differences in size or appearance of males and females
Inbreeding
A special form of nonrandom mating in which genetically related individuals mate with each other
Which agents of microevolution tend to increase genetic variation within populations, and which ones tend to decrease it?
Mutation and gene flow tend to increase genetic variation within population and natural selection and genetic drift tend to decrease it
Which mode of natural selection increases the representation of the average phenotype in a population?
Stabilizing selection increases the representation of the average phenotype in a population
In what ways is sexual selection like directional selection?
Sexual selection, like directional selection, favors extreme phenotypes.
balanced polymorphism
The maintenance of 2 or more phenotypes in fairly stable proportions over many generations
heterozygote advantage
an evolutionary circumstance in which individuals that are heterozygous at a particular locus have higher relative fitness that either homozygote
frequency-dependent selection
a form of natural selection in which rare phenotypes have a selective advantage simply because they are rare
neutral variation hypothesis
An evolutionary hypothesis that some variation at gene loci codin g for enzymes and other soluble proteins is neither favored nor eliminated by natural selection
How does the diploid condition protect harmful recessive alleles from natural selection?
Diploidy protects harmful recessive alleles because dominant alleles mask their effects in heterozygotes
What is balanced polymorphism?
A balanced polymorphism is one in which 2 or more phenotypes are maintained in fairly stable proportions over many generations
Why is the allele that causes sickle-cell disease very rare in human populations that are native to northern Europe?
The sickle-cell allele is rare in Northern Europe because in the absence of the malarial parasite, it confers no advantage on individuals that carry it.
adaptation
the accumulation of adaptive traits over time; examples that range across all levels of biological organization, from the molecular to the ecological
How can a biologist test whether a trait is adaptive?
The adaptive value of a trait can be evaluated by comparing closely related species that live in different environments
Why are most organisms adapted to the environments in which their parents lived?
Natural selection preserves traits that were useful when the organisms subject to selection were alive and reproducing
