Bio Ch. 13 Study

Suppose that, with regard to a particular gene with two alleles, A and a, we know that 60% of the alleles in the gene pool of a particular large population are A. We observe this population for five generations, during which we know that no mutation, selection, or migration has occurred. After this period, the frequency of the a allele is expected to be _____.

0.4 ; If 60% of the alleles are A, p = 0.6. Because q = 1 - p, the frequency of the a allele must be 0.4. The conditions are compatible with equilibrium, so those frequencies should be maintained.

Approximately one out of every 2,500 Caucasians in the United States is born with the recessive genetic disorder cystic fibrosis. According to the Hardy-Weinberg equilibrium equation, approximately how many people are carriers?

1 in 25 ; If q2 equals 1/2,500, then q equals 1/50, p equals 49/50, and 2pq equals approximately 1/25.

Which of the following lists of assumptions was part of Charles Darwin's theory of natural selection?

1. Organisms vary in heritable ways. 2. Some traits improve the survival and reproduction of individuals who possess them. 3. Populations produce more offspring than their environment can support, so individual organisms must compete for limited resources. 4. Earth and its life are very old.

modification

1. The phrase Darwin used to describe his broad theory of evolution is ''descent with modification.''

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

2-3

unity

2. All of life is related through common ancestry, accounting for the unity of life.

diversity

3. The diversity of life arises from the adaptation of species to different habitats over long spans of time.

natural selection

4. Darwin proposed a mechanism for how evolution occurs, which he called natural selection.

inherited traits

5. Two key observations underlying natural selection are that members of a population vary in their inherited traits and that all species can produce more offspring than the environment can support.

offsping

6. Darwin inferred that those organisms with traits best suited to the environment tend to leave more offspring than other members of a population.

adaptions

7. This unequal reproduction in a population leads to the gradual accumulation of adaptations to the environment.

If color is an inherited trait in beetles, and birds are more likely to eat brown beetles than green beetles,

the frequency of the green allele will increase.

Genetic drift is a process based on _____.

the role of chance. Genetic drift requires a small sample size.

A mutation occurs when _____.

there is a change in the DNA sequence of a gene

disruptive natural selection

A form of selection that operates in favor of extremes and against intermediate forms, selecting against the mean. favors phenotypes at both ends of a range over intermediate phenotypes. This type of selection may occur when the habitat is varied.

Of the scenarios below, which represents the occurrence of evolution at its smallest scale?

A pesticide spray is heavily used on a particular farm. Initially it kills 98% of the grasshoppers on contact. Over several generations, the local grasshopper population becomes resistant to the pesticide through inheritance of resistance alleles. Other nearby grasshopper populations do not change in any noticeable way.

Which of the following is a true statement about Charles Darwin?

A. He proposed natural selection as the mechanism of evolution.

Which best describes the fossil record?

A. The fossil record is the highly ordered sequence in which fossils are found in layers of sedimentary rock.

Which of these individuals is a homozygous genotype?

AA

Suppose that every few years, all people over 6 feet tall do not have any children. How will this affect the human population?

Alleles that promote "tallness" will decrease in frequency. A reduction in "tallness" alleles is the change expected as a result of this type of selection.

In natural selection, _____ determine which phenotypes are successful

B. current conditions in the local environment

In a species of snail, dark-shelled individuals are better hidden from bird predators in the shady forest, while light-shelled individuals are better hidden in well-lit brushy edge areas. If there were no areas of intermediate brightness in this habitat,which type of selection would act on shell color in these snails?

Disruptive selection

Color is an inherited trait in beetles. If brown beetles move into a population from a nearby island, which of the following statements is correct?

Gene flow causes the frequency of the brown allele to increase.

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.

What does Dr. Carroll mean when he says, "while mutation is random, natural selection is not"?

Mutations for advantageous traits are more likely to be passed on to the next generation. Natural selection favors some mutations. Natural selection acts on traits.

Natural selection and evolution are two terms that are sometimes confused, even by first year biology students. What is the relation between natural selection and evolution?

Natural selection is one of several mechanisms of evolution; Modern species evolved from ancestral forms, and natural selection is the main mechanism for adaptation, but other forms of microevolution also contribute to evolutionary change.

Which of the following is a misconception regarding natural selection?

Natural selection progressively refines organisms' adaptations, eventually leading to perfection. Submit

Consider a hypothetical insect population of 100 individuals. Two equally represented alleles (A and a) exist for a particular gene. Which scenario is an example of microevolution in this population?

The population is exposed to a toxin that kills individuals with the A allele. After exposure to the toxin the population has 25 surviving individuals, and 95% of them have the aa genotype.

A population of small fish lives in a lake with a sandy bottom. The major predator of these fish is a wading bird that hunts by sight. Most of the fish are light sandy brown, but about 10% are mottled. The color pattern is heritable. A construction company dumps a load of gravel in the bottom of the lake, giving it a mottled appearance. Which of these statements presents the most accurate prediction?

The proportion of mottled fish will increase over time. The mottled fish will tend to escape predation because they are camouflaged against the mottled lake bottom, and so the mottled fish will be able to leave more offspring.

Sickle-cell disease is a debilitating disease that results from being homozygous recessive for the "sickle-cell allele" of a hemoglobin gene. Why is the allele present and even common in many human populations?

The sickle-cell allele confers malaria resistance to heterozygotes. In some regions where malaria is common, heterozygotes have an advantage over both homozygotes, and their reproductive success maintains the recessive allele at a high frequency in the population. Submit

Why do dark-colored rock pocket mice on dark lava flows have white bellies?

There is no selection for dark bellies by visual predators.

Why did dark-colored rock pocket mice first appear in a population of light-colored rock pocket mice?

They have a genetic mutation that affects their fur color.

Mutations are always __________.

a change in an individual's DNA

Natural selection is best described as ____

a filtering process that fine-tunes the traits of populations by sorting among existing, randomly produced variations

Which of the following are causes of evolutionary change?

all mutation, natural selection, gene flow, genetic drift

HIV has become an important source of mortality for humans. If AIDS persists as a major factor for humans for many generations in the future, natural selection theory predicts that _____.

any heritable traits that help humans survive and reproduce in the presence of AIDS should become more frequent over time

A large population of mice is isolated on an island. There are two varieties of the mice, brown and gray. Their fur colors closely match the gray rock outcrops and brown soils of the island. Hawks are their main predators. This situation most likely reflects the outcome of __________.

disruptive natural selection ; The hawks will catch the mice they see best in each environment, favoring the maintenance of two different morphs in a patchy environment.

directional selection

favors phenotypes at one end of a range and is common in periods of environmental change.

Stabilizing selection

form of natural selection in which individuals near the center of a distribution curve have higher fitness than individuals at either end of the curve favors intermediate phenotypes, selecting against phenotypes at both ends of a range and reducing variation.

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

gene flow

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

gene pool. All the alleles of all the genes of a population make up a gene pool.

The evolution of populations due to chance is

genetic drift

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

genetic drift. Modern travel and migration decreases the chances of there being a small, isolated population.

In a population with brown and green alleles for color, genetic drift

has more effect on the evolution of a small population.

mate choice

in a type of sexual selection often called mate choice, individuals of one sex (usually females) are choosy in selecting their mates. This choice is often based on the showy appearance or behavior of the male.

Intrasexual selection

is a type of sexual selection in which individuals of one sex (usually males) compete directly for mates. This may involve ritualized displays or physical combat.

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

The original source of all genetic variation is __________.

mutation

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

nonsister chromatids of homologous chromosomes

Organisms that possess homologous structures probably __________.

C. share a common ancestor that also had this structure

As proposed by Darwin, what sorts of traits are favored by natural selection?

D. Heritable traits that help individuals survive and reproduce more successfully than others in the same population.

What was significant to Darwin about the fauna and flora of the Galápagos Islands?

D. The species were similar to South American species, indicating common descent, but they had been extensively modified and were well-adapted to island life.

sexual dimorphism

Differences in physical characteristics between males and females of the same species.

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.

Remember that color is an inherited trait in beetles. Which of the following is an example of natural selection?

Green beetles leave more offspring than brown beetles because they are better at finding food.

Which example below presents a misconception about how antibiotic resistance develops?

Individual bacteria and viruses become immune to antibiotics after they are exposed to them. Eventually the antibiotics are useless. Antibiotics have no effect on viruses, so this is one common misconception. More importantly, antibiotic resistance arises over several bacterial generations as resistant bacteria flourish and vulnerable strains die out. Although they are usually rare, the resistance traits are often present before the antibiotic is first used.

Disruptive selection causes both extreme phenotypes (light and dark shells) to be favored over the intermediate phenotype.

Stabilizing selection ; Stabilizing selection does not change the mean of the population; only the extreme phenotypes (large and small lizards) become less common

In the normal course of evolution and adaptation, what is the most likely way for wings to develop in a tetrapod (four-limbed organism)?

The forelimbs (or possibly hind limbs) will be used for the new purpose of flight. This new function will arise through many gradual steps, and there will be aspects of the wing that reflect its history and are not perfectly suited for flight. Every adaptation stems from some previous feature or structure of an organism. Natural selection starts with existing variation and gradually remodels it to fit new environments and new functions.