Chapter 23

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

nonsister chromatids of homologous chromosomes (This process produces chromosomes containing genes inherited from both parents.)

how quickly could evolution take place, going from the simplest light-sensitive cells to a fully-functioning eye?

over the course of 400,000 generations

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

Different finch species have beaks of different shapes and sizes. What do these beak differences tell us?

Different finch beak shapes are evidence that finch species adapted to different environments over many generations.

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.

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.)

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

Gene pool

Which of these individuals is a homozygous genotype?

AA

_____is the migration of individuals or gametes.

gene flow

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.

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

genetic drift

Every few years a giant axe chops off the head of every person who is over 6 feet tall. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency.

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 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.

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.

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.

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.

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

gene flow

Genetic drift is a process based on _____.

the role of chance

The film defines species as populations whose members don't interbreed. What keeps different Galápagos finch species from mating?

-Individuals recognize and only respond to songs of their own species. -Males only court females that have a similar beak and similar size. -Geographic isolation and different environments led to changes in traits that affected mating.

gene flow

-can introduce new alleles into a population's gene pool -a result of the movement of fertile individuals or their gametes

genetic drift

-causes allele frequencies to fluctuate randomly -responsible for the bottleneck effect -responsible for the founder effect

Natural Selection

-consistently causes a population to become better adapted to its environment -cannot cause a harmful allele to become more common -a result of differential success in reproduction

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.

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.

Which of the following best describes what we can determine about the evolution of the eye?

A variety of species exist that are likely to be similar to common ancestors whose eyes evolved to different degrees over time.

What is the mechanism & effect on allele frequencies? During an extreme heat wave, plants with white flowers survive better

M- natural selection F- frequency of white allele increases

What is the mechanism & effect on allele frequencies? A person uproots the five closest plants, which all happen to have white flowers

M-Genetic drift F- frequency of purple allele increases

What is the mechanism & effect on allele frequencies? Workers from a nearby greenhouse accidentally introduce white flower seeds into this population's habitat

M-gene flow F- frequency of white allele increases

Genetic evidence supports which of the following explanations for the presence of 13 different finch species on the Galápagos islands?

Many years ago, a small population of a single finch species migrated to the islands and evolved into the current 13 species.

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

Mutation

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.)

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? -Even if allele A1 is dominant to allele A2 , it does not increase in frequency. -If allele frequencies in a population are given by p and q, then genotype frequencies will be given by p 2, 2pq, and q 2 for generation after generation. -The genotype frequencies in the offspring generation must add up to two. -When alleles are transmitted according to the rules of Mendelian inheritance, their frequencies do not change over time.

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.)

A giraffe and a mouse (both mammals) have the same number of vertebrae in their neck and spine. Which of the following accounts for this?

The vertebrae in their neck and spine are homologous because they share a common ancestor.

Sharks (which are fish) and dolphins (which are mammals) are both shaped like a torpedo. Which of the following accounts for this?

Their shape arose through convergent evolution, since that shape is beneficial for animals living in the ocean.

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.

Which of the following best describes the likely evolutionary steps that led to a complex eye like we see in humans?

a flat sheet of light-sensitive cells; light-sensitive cells in a cup; a pinhole camera without a lens; a pinhole camera with a lens

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

metaphase I

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

microevolution

What does the wide variety of different types of animal eyes represent?

the intermediate forms that probably occurred in the common ancestors of today's animals