BSC 2011: Ch 23

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the recessive allele in this population?

0.8

In a population that is in Hardy-Weinberg equilibrium, 64% of the individuals express the recessive phenotype for a particular gene locus. What is the expected frequency of the dominant allele in this population?

0.2

All the genes in a population are that population's _____.

gene pool

Rearrangement of gene loci would most likely be harmful, and it does not generate new ___ material.

genetic

Modern travel along with migration reduces the probability of _____ having an effect on the evolution of humans.

genetic drift

Population variation is the result of ___ ___ in coding regions of DNA.

genetic variation

Sexual recombination includes the shuffling of chromosomes in __________ and fertilization.

meiosis

Homologous pairs of chromosomes are lined up independently of other such pairs during _____.

metaphase 1

The ease with which humans travel across the globe is likely to increase _____.

gene flow

Ongoing genetic drift is likely to have substantial effects on the ___ ___ until the population becomes large enough that chance events have less impact.

gene pool

A change in nucleotide sequence describes the result of any type of ___ but is not in and of itself a type of ___

mutation; mutation

It is true that ___ are very rare, but they are important in that they are the ultimate source of genetic variation.

mutations

All of the following conditions are required for Hardy-Weinberg equilibrium except __________.

natural selection

Neutral variation refers to genetic variations that have little or no impact on __ __

reproductive success.

If the phenotype of a heterozygote is intermediate to the phenotypes of both homozygotes, the heterozygote advantage is a form of ___ selection.

stabilizing

A hurricane hits a small island, killing all but a few members of a bird population. This is an example of __________.

the bottleneck effect

In the Hardy-Weinberg equation, 2pq represents __________.

the expected frequency of the heterozygous genotype

In the Hardy-Weinberg equation, q2 represents __________.

the expected frequency of the homozygous recessive genotype

A storm separates a small number of birds in a migrating population. These birds end up at a destination different from where they usually migrate and establish a new population in this new area. This is an example of __________.

the founder effect

In a large population of randomly breeding organisms, the frequency of a recessive allele is initially 0.3. There is no migration and no selection. Humans enter this ecosystem and selectively hunt individuals showing the dominant trait. When the gene frequency is reexamined at the end of the year, __________.

the frequency of the homozygous dominants will go down, the frequency of the heterozygous genotype will go down, and the frequency of the homozygous recessives will go up

The sickle-cell allele, which is recessive, causes anemia but confers resistance to malaria in individuals who possess it. However, homozygous recessive individuals often die from anemia but not from malaria, and homozygous dominant individuals do not have anemia but could die from malaria. Heterozygous individuals have the highest relative fitness. This is an example of __________.

the heterozygote advantage

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

the reshuffling of alleles in sexual reproduction

Genetic drift is a process based on _____.

the role of chance

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Stabilizing selection actually reduces ___ and maintains the status quo for a particular phenotypic character.

variation

In the context of populations, how do we define evolution?

Evolution is a change in a population's allele frequencies over generations.

Which of the following statements explains why male peacocks with brightly colored feathers are more prevalent than those with plain colors?

Female peacocks choose the showiest males as mates, causing this trait to be more prevalent in the population.

Which statement below is true about sexual selection?

Sexual selection can result in sexual dimorphism—marked differences between the sexes in secondary sexual characteristics that are not associated directly with reproduction.

The Hardy-Weinberg model makes the following assumptions: no selection at the gene in question; no genetic drift; no gene flow; no mutation; random mating.

True

At what level does gene variability quantify genetic variation?

Whole-gene

Which of the following is the best example of gene flow?

Wind blows pollen from one population of plants to another and cross-fertilization occurs.

Neutral variations are differences in DNA sequence that do not confer a selective ___ or ___.

advantage or disadvantage

The gene pool of a population consists of __________.

all copies of every type of allele at every locus in all members of the population

In a population that is not evolving, ___ and ___ ___ will remain constant from generation to generation, provided that only ___ ___ and ___ of alleles are at work. Such a population is said to be in Hardy-Weinberg equilibrium

allele and genotype frequencies; Mendelian segregation and recombination

Even a point mutation in a gene that encodes a protein will have no effect on the protein's function if the ___ ___ composition is not changed; and even when there is a change in the ___ ___, the change may not affect the protein's shape or function.

amino acid; amino acid

Heterozygote advantage is one mechanism of ___ ___

balancing selection.

But even if a population that has passed through a ___ ___ ultimately recovers in size, it may have low levels of genetic variation for a long period of time—a legacy of the ___ ___ that occurred when the population was small

bottleneck; genetic drift

Phenotypic variation can be the result of mutations in the ___ regions of DNA.

coding

Protein variability can be the result of mutations in ___ regions of DNA.

coding

Because the genetic code is redundant, even point mutations in genes that code for proteins may have little effect because they do not alter the amino acid ___.

composition

An important source of variation begins when genes are duplicated due to errors in meiosis (such as unequal ___ ___), ___ during DNA replication, or the activities of ___ elements.

crossing over; slippage; transposable

A population in Hardy-Weinberg equilibrium is not ___, and may exhibit genetic variation.

evolving

Stabilizing selection __________.

favors intermediate variants in a population

The ___ ___ occurs when a few individuals become isolated from a larger population and the smaller group establishes a new population whose gene pool differs from that of the source population.

founder effect

Which of the following statements is not a part of the Hardy-Weinberg principle?

The genotype frequencies in the offspring generation must add up to two.

Which type of mutation plays the most important role in increasing the number of genes in the gene pool?

Duplication

___ of large chromosome segments, like other chromosomal aberrations, are often harmful, but the ___ of smaller pieces of DNA may not be. Gene ___ that do not have severe effects can persist over generations, allowing mutations to accumulate. The result is an expanded genome with new genes that may take on new functions.

Duplications; duplication; duplications

___ ___ is the random mixing of gametes in a population.

Random mating

Which of the following sets of conditions is required for Hardy-Weinberg equilibrium?

Random mating, no natural selection, and a large population

Which of the following evolutionary forces consistently results in adaptive changes in allele frequencies?

Selection

The expected frequency of the homozygous recessive genotype is represented by __

q2

Which of these individuals is a homozygous genotype?

AA

In human gamete production there is an average of _____ crossover events per chromosome pair.

2-3

In a certain group of people, 4% are born with sickle-cell disease (homozygous recessive). If this group is in Hardy-Weinberg equilibrium, what percentage of the group is heterozygous for the sickle hemoglobin allele?

32%

Which of the following statements correctly describe(s) characteristics of genetic drift?

All of the listed responses are correct. (It is significant in small populations.It can lead to a loss of genetic variation in a population.It can cause harmful alleles to become fixed in a population.It can cause allele frequencies to change at random.)

Natural selection leads to adaptation, but there are many organisms on Earth that exhibit characteristics that are less than ideal for their environment. Which of the following statements correctly explain(s) this?

All of the listed responses are correct. (Chance, natural selection, and the environment interact. Adaptations are often compromises. Evolution is limited by historical constraints. Selection can act only on existing variations.)

___ and ___ ___ do not change in a population that is in Hardy-Weinberg equilibrium.

Allele and genotype frequencies

Which of the following statements correctly describes a population in Hardy-Weinberg equilibrium?

Allele and genotype frequencies in the population will remain constant from generation to generation.

Which type of selection maintains stable frequencies of two or more phenotypic forms in a population?

Balancing selection

___ ___ occurs when natural selection maintains two or more forms in a population.

Balancing selection

Antibiotic resistance in bacteria is an example of which of the following?

Directional selection

___ ___ is selection for a single phenotypic form; selection for two or more forms is ___ ___.

Directional selection; balancing selection

A population of squirrels is preyed on by small hawks. The smaller squirrels can escape into burrows. The larger squirrels can fight off the hawks. After several generations, the squirrels in the area tend to be very small or very large. What process is responsible for this outcome?

Disruptive selection

Which of the following are basic components of the Hardy-Weinberg model?

Frequencies of two alleles in a gene pool before and after many random matings

___ variability describes genetic variation at the whole-gene level, which would not be the result of mutations in noncoding regions of DNA.

Gene

___ ___ is the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes.

Gene flow

___ ___ is the process in which chance events can also cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations.

Genetic drift

Which of the following would seem to be an example of neutral variation?

Human fingerprints

Which of the following can form entirely new alleles?

Mutation

Which of the following evolutionary forces could create new genetic information in a population?

Mutation

Chance events can cause allele frequencies to fluctuate unpredictably from one generation to the next, especially in small populations, a process called ___ ___. Certain circumstances can result in ___ ___ having a significant impact on a population. A sudden change in the environment, such as a fire or a flood, may drastically reduce the size of a population. A severe drop in population size can cause the ___ ___, that reduces its size. By chance alone, certain alleles may be overrepresented among the survivors, others may be underrepresented, and some may be absent altogether.

genetic drift; genetic drift; bottleneck effect

If individuals who are ___ at a particular locus have greater fitness than do both kinds of ___, they exhibit the heterozygote advantage. In such a case, natural selection tends to maintain two or more ___ at that locus. Note that the heterozygote advantage is defined in terms of , ___ not ___.

heterozygous; homozygotes; alleles; genotype not phenotype

The equation for Hardy-Weinberg equilibrium states that at a locus with two alleles, the three genotypes will appear in the following proportions: p2 is the expected frequency of one of the ___ genotypes, 2pq is the expected frequency of the ___ genotype, and q2 is the expected frequency of the other ___ genotype.

homozygous; heterozygous; homozygous

The expected frequency of the recessive allele is represented by __

q

Point mutations in noncoding regions of DNA result in __________.

neutral variation

Crossing over, resulting in an increase in genetic variation, occurs between _____.

nonsister chromatids of homologous chromosomes

The expected frequency of the dominant allele is represented by __

p

The expected frequency of the homozygous dominant genotype is represented by __

p2