Bio Chapter 21

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a generation-to-generation change in allele frequency.


The original source of all genetic variation is _____.


According to the Hardy-Weinberg theorem, the frequencies of alleles in a population will remain constant if _____ is the only process that affects the gene pool.

sexual reproduction

does not change the frequency of alleles in the gene pool.

sexual reproduction

The evolutionary effects of genetic drift are greatest when _____.

the population size is small

What situation most likely explains the occasional high frequency of certain inherited disorders among human populations established by a small population?

founder effect

No two people are genetically identical, except for identical twins. The main source of genetic variation among human individuals is

reshuffling of alleles due to sexual reproduction

In evolutionary terms, an organism’s fitness is measured by its _____.

contribution to the gene pool of the next generation

Blue poppies native to China were grown at a plant-breeding center in California. The plants with the thickest leaves were most likely to survive and reproduce in the drier climate. After several generations, the percentage of thick-leaved plants had increased by 42%. This adaptation of the poppies to their new environment is due to _____.

directional selection

What is the only evolutionary mechanism that consistently leads to adaptive evolution?

natural selection

_______ has a "sorting" effect, it consistently increases the frequency of alleles that improve the match between an organism and its environment.

natural selection

How does diploidy help to preserve genetic variation?

It allows recessive alleles that may not be favored in the current environment to be preserved in the gene pool by propagation in heterozygotes.

Natural selection tends to decrease

genetic variation

Recessive alleles are shielded from natural selection in


does natural selection act on individuals or populations?


a change in allele frequencies in a population over generations


the mechanisms that cause allele frequencies to change

natural selection, genetic drift, gene flow

the transfer of alleles from one population to another

gene flow

which of the three causes adaptive evolution

natural selection

how genetic variation is measured at the molecular level

nucleotide variability

does nucleotide variability result in phenotypic variation?


how do you measure gene variability

the average % of loci that are heterozygous

What often reflects genetic variation

phenotypic variation

the product of inherited genotype and environmental influence


natural selection can act on phenotypic variation that has a

genetic component

4 sources of genetic variation

mutation, gene duplication, rapid reproduction, sexual reproduction

ultimate source of genetic variation


only mutations in cells that produce _____ can be passed to offspring


one way that mutations can be helpful

ones that alter protein production

what equation can be used to test whether a population is evolving

hardy weinberg equation

the most important genetic variation for microevolution in populations

allelic variation

a localized group of individuals capable of interbreeding and producing fertile offspring


consists of all the alleles for all loci in a population (the sum of all alleles in a population)

gene pool

the location of a gene on a chromosome


the relative quantity of a genotype for a gene in a population

genotype frequency

the relative quantity of an allele for one gene in a population

allele frequency

states that frequencies of alleles and genotypes in a population remain constant from generation to generation

hardy weinberg principle

allele frequencies will not change if

gametes contribute to the next generation randomly

what preserves genetic variation in a population

mendelian inheritance

the hardy weinberg principle describes a population that is

not evolving

describes the constant frequency of alleles in a not evolving population

hardy weinberg equilibrium

describes how allele frequencies fluctuate unpredictably from one generation to the next

genetic drift

tends to reduce genetic variation through losses of alleles

genetic drift

two examples of genetic drift

founder effect and the bottleneck effect

genetic drift that occurs when a few individuals become isolated from a larger population

founder effect

genetic drift that can result from a drastic decrease in population size due to a sudden environmental change

bottleneck effect

two examples of gene flow

movement of reproductive individuals, movement of gametes

the ability of alleles to be passed on to another generation


the only mechanism that consistently causes adaptive evolution

natural selection

an increase in the frequency of alleles that improve fitness

adaptive evolution

3 modes of natural selection

directional selection, disruptive selection, stabilizing selection

natural selection that favors individuals at one end of the phenotypic range

directional selection

natural selction that favors individuals at both extremes of the phenotypic range

disruptive selection

favors intermediate variants and acts on extreme phenotypes

stabilizing selection

natural selection for mating success

sexual selection

marked differences between the sexes in secondary sexual characteristics

sexual dimorphism

competition among individuals of one sex (usual males) for mates of the opposite sex

intrasexual selection

occures when individuals of one sex (usually females) are choosy in selecting their mates

intersexual selection

suggests that if a trait is related to male genetic quality of health, both the male trait and female preference for that trait should increase in frequency

good genes hypothesis

genetic variation that does not give a selective advantage or disadvantage

natural variation

heterozygotes can carry recessive alleles that are hidden from the effects of selection


occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population

balancing selection

occurs when heterozygotes have a higher fitness than do both homozygotes

heterozygote advantage

occurs when the fitness of a phenotype declines if it becomes to common in the population

frequency dependent selection

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