AP Bio Ch. 23: The Evolution of Populations

a cline

a gradual change in a trait along a geographic axis.

Which variable is likely to undergo the largest change in value resulting from a mutation that introduces a new allele into a population at a locus for which all individuals formerly had been fully homozygous?

average heterozygosity

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

contribution to the gene pool of the next generation Those organisms with adaptations best suited to the current environment will make the most significant contribution to the next generation.

The original source of all genetic variation is _____.

mutation Mutation is, in itself, very important to evolution because it is the original source of the genetic variation that serves as the raw material for evolution.

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

non-sister chromatids of homologous chromosomes This process produces chromosomes containing genes inherited from both parents.

The evolutionary effects of genetic drift are greatest when _____.

the population size is small Changes in the gene pool of a small population are frequently due to genetic drift.

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. Use the Hardy-Weinberg equation to predict the frequency of homozygous recessive cats in the next generation.

0.16

A fruit fly population has a gene with two alleles, A1 and A2. Tests show that 70% of the gametes produced in the population contain the A1 allele. If the population is in Hardy-Weinberg equilibrium, what proportion of the flies carry both A1 and A2?

0.42

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. Use the Hardy-Weinberg equation to predict the frequency of heterozygous cats in the next generation.

0.48

Which of these gametes contain one or more recombinant chromosomes?

B, C, F, and G These gametes carry chromosomes produced as a result of crossing over.

Long necks make it easier for giraffes to reach leaves high on trees, while also making them better fighters in "neck wrestling" contests. In both cases, which kind of selection appears to have made giraffes the long-necked creatures they are today?

Directional selection Directional selection drives the average of the population in one direction, in this case, toward longer necks.

Black-bellied seedcrackers have either small beaks (better for eating soft seeds) or large beaks (better for hard seeds). There are no seeds of intermediate hardness; therefore, which kind of selection acts on beak size in seedcrackers?

Disruptive selection Disruptive selection causes both extreme phenotypes (large and small beaks) to be favored over the intermediate phenotypes.

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

Mutation Mutations, which are changes in a cell's DNA, can introduce new genetic information in a population.

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

Selection Selection is the only evolutionary force that consistently results in adaptation. Mutation without selection and genetic drift are random processes that may lead to adaptive, maladaptive, or neutral effects on populations.

Rabbit ear size tends to decrease as latitude increases. This is an example of _____.

a cline A cline is a gradual change in a trait along a geographic axis.

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

2-3 These crossover events increase the genetic variation among gametes.

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 heterozygotes.

What is true of microevolution?

It is the kind of evolution that can change the relative abundance of a particular allele in a gene pool over the course of generations. Microevolution is a generation-to-generation change in allele frequency.

What genotype frequencies are expected under Hardy-Weinberg equilibrium for a population with allele frequencies of p = 0.8 and q = 0.2 for a particular gene?

The expected genotype frequencies are 0.64, 0.32, and 0.04 for A1A1, A1A2 , and A2A2 , respectively. The expected frequency of the A1A1 genotype is p 2 = (0.8)(0.8) = 0.64; the expected frequency of the A1A2 genotype is 2pq = 2(0.8)(0.2) = 0.32; the expected frequency of the A2A2 genotype is q 2 = (0.2)(0.2) = 0.04. To verify your calculations, confirm that the three frequencies add up to one.

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. What is the frequency of cats with short tails in the population?

0.16

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. What is the frequency of cats that are homozygous dominant in the population?

0.36

What is the frequency of the A1A2 genotype in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?

0.4 The calculation to determine the frequency of the A1A2 genotype is: 80 A1A2 individuals / (20 + 80 + 100) total individuals = 0.4, the frequency of the A1A2 genotype.

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. Use the Hardy-Weinberg equation and your answer to question 7 (0.16) to estimate the frequency of the recessive allele t in the next generation.

0.40

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. What is the frequency of the t allele in the gene pool of this population?

0.40

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. What is the frequency of the T allele in the gene pool of this population?

0.60

A hypothetical population of 500 cats has two alleles, T and t, for a gene that codes for tail length. (T is completely dominant to t.) The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy-Weinberg equilibrium. Recall that the Hardy-Weinberg equation is p 2 + 2pq +q 2 = 1. What is the frequency of cats with long tails in the population?

0.84

One out of 10,000 babies born in North America is affected by cystic fibrosis, a recessive condition. Assuming that the North American human population is in Hardy-Weinberg equilibrium for this trait, what percentage of the population is heterozygous for this trait? (Remember the equation for a population in Hardy-Weinberg equilibrium: p2 + 2pq + q2 = 1.)

2% If the trait is in Hardy-Weinberg equilibrium, then its frequency is not changing in the population from generation to the next.

If, on average, 46% of the loci in a species' gene pool are heterozygous, then the average homozygosity of the species should be ______.

54%

You read about soapberry bugs and select the correct statement describing relative fitness in these individuals.

A soapberry bug with high relative fitness has a relatively high number of offspring that survive to reproductive age. Relative fitness is defined by the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals.

Which type of selection tends to increase genetic variation?

Disruptive selection Disruptive selection eliminates phenotypes near the average and favors the extreme phenotypes, resulting in increased genetic variation in a population.

True or false? Heterozygote advantage refers to the tendency for heterozygous individuals to have better fitness than homozygous individuals. This higher fitness results in less genetic variation in the population.

False Heterozygote advantage results in more genetic variation in the population.

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. Hardy and Weinberg were trying to determine how and whether allele frequencies in a population change from one generation to the next.

Women often have complications during labor while giving birth to very large babies, whereas very small babies tend to be underdeveloped. Which kind of selection is most likely at work regarding the birth weight of babies?

Stabilizing selection Stabilizing selection causes no change in the average of the population; extreme phenotypes (in this case, large and small babies) become less common.

What is the frequency of the A1 allele in a population composed of 20 A1A1 individuals, 80 A1A2 individuals, and 100 A2A2 individuals?

The frequency of the A1 allele is 0.3. The frequency of the A1 allele is p = (number of A1 alleles) / (total of all alleles) = [(2 ( 20) + 80] / [(2 × 20) + (2 × 80) + (2 × 100)] = 0.3.

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. This statement is not true; the genotype frequencies in the offspring generation must add up to one.

In a bell-shaped curve, the x-axis (horizontal direction) of the graph represents which of the following?

The value of a particular characteristic; characteristics of an organism can include such traits as size and color. The value of the characteristic increases from left to right.

There are 40 individuals in population 1, all with genotype A1A1, and there are 25 individuals in population 2, all with genotype A2A2. Assume that these populations are located far from each other and that their environmental conditions are very similar. Based on the information given here, the observed genetic variation is most likely an example of ______.

genetic drift

Allele frequencies in a gene pool may shift randomly and by chance. What is this random shift called?

genetic drift Genetic drift is due to chance events that alter allele frequencies.

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

metaphase I This describes metaphase I.

Which of the following are causes of evolutionary change?

mutation genetic drift natural selection gene flow

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

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

Sparrows with average-sized wings survive severe storms better than those with longer or shorter wings, illustrating _____.

stabilizing selection.

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

Small Aristelliger lizards have difficulty defending territories, but large lizards are more likely to be preyed upon by owls. Which kind of selection acts on the adult body size of these lizards?

Stabilizing selection Stabilizing selection causes no change in the average of the population; extreme phenotypes (large and small lizards) become less common.

True or false? 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 These are the five assumptions of the Hardy-Weinberg model.

Generation-to-generation change in the allele frequencies in a population is _____.

microevolution Generation-to-generation change in the allele frequencies in a population is the definition of microevolution.