chapter 22

The only survivors of a colony on Venus are a man and a woman, who both happen to originally be from southern Ukraine. Their descendants will show the effect of \____.

genetic drift

Mammals living in cold environments tend to have \____ bodies and \____ appendages than species living in warm environments.

larger; shorter

In many species, sexual selection is the most probable cause of \____, differences in the size or appearance of males and females.

sexual dimorphism

If a lethal mutation occurs in a dominant allele, \____ individuals will die from its effects.

both homozygous dominant and heterozygous

The high incidence of Ellis-van Creveld syndrome among the Old Order Amish population is caused by \____.

inbreeding

Genetic variation has two potential sources:

the production of new alleles and the rearrangement of existing alleles.

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 described in Figure 21.6, 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 population.

The sum of all gene copies at all gene loci in all individuals is called

population's gene pool.

the percentages of individuals possessing each genotype.

genotype frequencies,

the relative abundances of the different alleles

allele frequencies

genetic equilibrium is possible only if all of the following conditions are met:

1 .No mutations are occurring.

2 .The population is closed to migration from other populations.

3 .The population is infinitely large.

4 .All genotypes in the population survive and reproduce equally well.

5 .Individuals in the population mate randomly with respect to genotypes.

For an autosomal gene locus, there are \____ possible genotypes and \____ possible alleles.

three; two

With the biological species concept, the process of speciation is frequently defined as the evolution of \____ between populations.

reproductive isolation

What is the difference between the genotype frequencies and the allele frequencies in a population?

Answer:

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?

Answer

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?

Answer

If genotype frequencies are not already in equilibrium, they will stop changing after one generation of random mating.

what are the processes that foster microevolutionary change

mutation, gene flow, genetic drift, natural selection, and nonrandom mating

Mutation

-a spontaneous and heritable change in DNA

-Introduces new genetic variation into population; does not change allele frequencies quickly

Gene flow

-Change in allele frequencies as individuals join a population and reproduce

-May introduce genetic variation from another population

Genetic drift

-Random changes in allele frequencies caused by chance events

-Reduces genetic variation, especially in small populations; can eliminate rare alleles

Natural selection

-Differential survivorship or reproduction of individuals with different genotypes

-One allele can replace another or allelic variation can be preserved.

Directional selection

shifts the mean phenotype toward the end of the distribution favored by natural selection.

Stabilizing selection

favors the mean phenotype over extreme phenotypes

Disruptive selection

decreases the frequency of the mean phenotype, but increases the frequencies of extreme phenotypes.

-After selection, the mean may be unchanged, but the variability among individuals has increased.

When people used artificial selection to produce the long body and short legs of a dachshund, which mode of selection did they use?

Dachshunds are the product of directional selection on two traits: body length was increased and leg length was decreased

On what developmental mechanism did sexual selection apparently act in the evolution of exaggerated horn size in male rhinoceros beetles?

Sexual selection apparently increased the sensitivity of horn-producing cells to the presence of insulin/IGF.

Which agents of microevolution tend to increase genetic variation within populations, and which ones tend to decrease it?

Answer

Mutation and gene flow tend to increase genetic variation within populations, 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 way is sexual selection like directional selection?

Answer

Sexual selection, like directional selection, favors extreme phenotypes.

How does the diploid condition protect harmful recessive alleles from natural selection?

Diploidy protects harmful recessive alleles from natural selection because dominant alleles mask their effects in heterozygotes.

What is a balanced polymorphism?

A balanced polymorphism is one in which two or more phenotypes are maintained in fairly stable proportions over many generations.

Why is the allele that causes sickle-cell anemia 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.

Polyploidy is a mechanism of sympatric speciation most common to \____.

plants

Genetic variations that confer no apparent selective advantage or disadvantage in a particular environment are said to be selectively

neutral

The stable presence of two or more phenotypes in a population is called a \____.

balanced polymorphism

Which scenario is an example of mechanical reproductive isolation?

two flowers that are pollinated by different insects

Andrew P. Hendry and colleagues discovered that Galápagos ground finches with small bills and ground finches with large bills were more common and had higher fitness than birds with bills of intermediate size, a demonstration of \____

disruptive selection.

If the gene pools of allopatric populations did not differentiate much during geographical separation, then upon reestablishing contact, the populations may interbreed and merge into one. This phenomenon is called \____.

species fusion

Research by Malte Andersson suggests the long tail feathers of male African widowbirds are a product of \____ selection because females are more strongly attracted to males with long tails than to males with short tails

intersexual

How do the morphological, biological, and phylogenetic species concepts differ?

The morphological species concept defines species based on morphological differences among them. The biological species concept defines species as populations that can successfully interbreed under natural conditions. The phylogenetic species concept defines a species as a cluster of populations with a recent shared evolutionary history.

What is clinal variation?

Clinal variation is a pattern of smooth variation along a geographical gradient.

A plant with a very small tubular type of flower that cannot be pollinated by a large honeybee is exhibiting which prezygotic isolating mechanism?

mechanical

Characters that exist in two or more discrete states are described as exhibiting \____.

qualitative variation

A hybrid zone is defined as an area where two populations may breed and produce \____.

viable, fertile offspring

With \____ , the frequency of the mean phenotype decreases while the frequencies of extreme phenotypes increase.

disruptive selection

Polyploidy refers to an individual \____ and occurs most often in \____.

with one or more additional sets of chromosomes; plants

Allopolyploidy is defined as \____ chromosome number due to \____.

increased; hybridization of different species

Natural selection exerts little or no effect on traits that appear during an individual's \____.

postreproductive life

Which combination is an example of prezygotic mechanisms of isolation?

mechanical and temporal isolation

Hybridization between different species is rare because it \____.

requires the breakdown of a barrier preventing interbreeding

Which scientist published the book titled Systematics and the Origin of Species in 1942?

Ernst Mayr

Species that live in different habitats exhibit \____ reproductive isolation.

ecological

Allopatric speciation typically occurs in two stages. The first stage is \____ of two populations and the second stage is \____.

geographic separation; reproductive isolation

The female reproductive tract of some Drosophila species blocks sperm of another species from reaching her eggs. This is an example of \____.

gametic isolation

Mendel inferred the genetic basis of \____, such as flower color in peas, by crossing plants with different phenotypes.

qualitative traits

To distinguish two organisms using the morphological species concept, a scientist would \____.

look at the appearance of two organisms

Most copies of rare recessive alleles exist in \____.

heterozygotes

Which reproductive isolating mechanism is displayed in a mule, the product of a cross between a horse and a donkey?

hybrid sterility

Research comparing chromosomal structure between the genomes of humans and other primates reveals that humans are most closely related to \____

chimpanzees

Dog breeders produced the long body and short legs of a dachshund by employing \____

directional selection.

If two species of lizards do not mate because their mating rituals differ greatly, they are exhibiting \____ reproductive isolation.

behavioral

Natural selection that shifts the adaptation of an entire population is known as \____.

directional selection

A zebroid is the sterile hybrid offspring of a horse and a zebra. This is an example of \____.

hybrid sterility

A species cluster is defined as a group of \____.

closely related species with a common ancestor

The development of penicillin-resistant bacteria represents an example of \____.

microevolution

According to the Hardy Weinberg principle, microevolution occurs when \____.

a population experiences a shift in allele frequencies

The biological species concept cannot be applied to \____.

. plants that reproduce asexually

Abrupt genetic changes that quickly lead to the reproductive isolation of a group of individuals will likely lead to \____.

sympatric speciation

Microevolutionary change resulting from the differential survivorship or reproduction of individuals with different genotypes is known as \____.

natural selection

Individuals with one sickle-cell allele and one normal hemoglobin allele are not affected by the malaria parasite because of \____.

heterozygote advantage

The biological species concept emphasizes the ability of individuals to \____.

interbreed and produce fertile offspring

If an organism with 64 chromosomes mates with a closely related organism with 62 chromosomes, the most likely result will be \____.

sterile offspring due to hybrid sterility

Many closely related duck species exhibit \____, the dramatic variation in the appearance of males but not females, which is an almost certain sign of \____.

sexual dimorphism; sexual selection

The agent of microevolutionary change that is most likely to introduce genetic variation from another population is referred to as

gene flow

Genetic drift will have a progressively larger impact on allele frequencies in a population as \____.

population size decreases

Identifying species based on evolutionary relationships is an example of the \____ concept.

phylogenetic species

A group of individuals of a single species that live together in the same place and time is referred to as a(n) \____.

population

What is the difference between prezygotic and postzygotic isolating mechanisms?

Prezygotic isolating mechanisms either prevent individuals of different species from mating or prevent sperm of one species from fertilizing the eggs of another. Postzygotic isolating mechanisms limit the survivorship or reproductive capability of hybrid individuals.

When a male duck of one species performed a courtship display to a female of another species, she interpreted his behavior as aggressive rather than amorous. What type of reproductive isolating mechanism does this scenario illustrate?

Answer