Lesson 22 (How Populations Evolve #1)

Imagine that four people are infected with HIV from a common source (an infected blood sample). Initially, the patients' HIV populations are genetically identical. By the time they develop full-blown AIDS, how would the viral populations of the four patients compare? a. Each patient's viral population would be unique, specifically adapted to deal with—and overcome—his or her unique immune system responses. b. The viral populations would still be genetically identical to each other and would be unchanged from the time of infection. c. The viral populations would have evolved to a new and more dangerous strain, but that strain would be identical across all four patients. This is the strain of virus found in every person suffering full-blown AIDS.

a. Each patient's viral population would be unique, specifically adapted to deal with—and overcome—his or her unique immune system responses.

Which option best describes the concept of an evolutionary tree diagram? a. Evolutionary trees relate species to each other by ancestry. An ancestor common to all of the species is placed at the root of the tree. Branch points are defined by homologous features that are shared by the descendant species along a particular branch. b. Evolutionary trees relate species to each other by adaptation. Species that are adapted to similar environments share branches on the tree of life. At the root is a common ancestor that could live in most environments known to occur on Earth. c. It is a diagram that shows how individuals are related to one another within a species. For humans, an example would be a family tree. d. It is a diagram that organizes species into groups based on their overall similarities and joins them into a tree of life.

a. Evolutionary trees relate species to each other by ancestry. An ancestor common to all of the species is placed at the root of the tree. Branch points are defined by homologous features that are shared by the descendant species along a particular branch. --> Evolutionary trees are hypotheses about how descent with modification has produced diverse species over evolutionary time.

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

inherited traits

Changes in allele frequencies in a population over time is _______.

microevolution

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

modification

A(n) _______ is a change in the nucleotide sequence of DNA.

mutation

Darwin proposed a mechanism for how evolution occurs, which he called ________.

natural selection

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

offspring

A(n) ________ is a group of individuals of the same species living in the same area that interact with each other.

population

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

unity

The total collection of alleles in a population at a given time is the population's _______.

gene pool

As in the previous question, suppose there is a population of 100 rabbits that have different fur patterns.In this population several generations ago, there were 60 FF rabbits, 20 Ff rabbits, and 20 ff rabbits. Over time, the population changed, and now there are 40 FF rabbits, 40 Ff rabbits, and 20 ff rabbits. Has microevolution occurred? Why or why not? a. Yes, because the allele frequencies have changed. b. Yes, because time has passed. c. No, because the population size has not changed. d. No, because the number of ff rabbits has not changed.

a. Yes, because the allele frequencies have changed. --> The allele frequencies have changed over time. Initially, the allele frequencies were F = 0.7 and f = 0.3. After time passed, the allele frequencies are now F = 0.6 and f = 0.4. Because the allele frequencies have changed, microevolution has occurred.

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 _____. a. any heritable traits that help humans survive and reproduce in the presence of AIDS should become more frequent over time b. AIDS should gradually become less variable with a lower mutation rate c. humans will develop weaker immune systems as an evolutionary response to natural selection d. individual humans will evolve to become immune to AIDS as long as they are exposed to it as young children

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

In natural selection, _____ determine which phenotypes are successful. a. current conditions in the local environment b. catastrophes that reduce the population to a very small number of survivors c. future (anticipated) environmental conditions d. chance events

a. current conditions in the local environment --> Natural selection occurs through an interaction between the environment and the variability inherent among individual organisms making up a population.

An important challenge to traditional (pre-1860) ideas about species was the observation that seemingly dissimilar organisms, such as hummingbirds, humans, and whales, have similar skeletal structures. This most directly suggested to biologists that __________. a. these seemingly dissimilar organisms might have evolved from a distant, common ancestor b. only the best-adapted organisms can survive c. advantageous changes can be passed along to offspring d. most evolution occurs rapidly following a mass extinction

a. these seemingly dissimilar organisms might have evolved from a distant, common ancestor --> Similarity in characteristics resulting from a common ancestor is known as homology, and such anatomical signs of evolution are known as homologous structures.

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

adaptations

A(n) ______ is an alternative version of a gene.

allele

Of the scenarios below, which represents the occurrence of evolution at its smallest scale? a. An individual organism begins as a single cell and develops into an adult, changing dramatically through a series of life stages. b. 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. c. Over many thousands of years, the beak shape of a bird species changes to exploit a new food source. d. An adult human moves from near sea level to a city high in the Andes Mountains. Her physiology changes to improve her performance in the thin atmosphere.

b. 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. --> There has been evolutionary (generation-to-generation, genetically based) change within a single population, the smallest scale of evolution.

Which statement would Darwin have disagreed with? a. Living species have arisen from earlier life-forms. b. Descent with modification occurs through inheritance of acquired characteristics. c. Species change over time. d. Descent with modification occurs by natural selection.

b. Descent with modification occurs through inheritance of acquired characteristics.

The human immune system cannot effectively suppress the HIV virus on its own. What key feature of HIV makes it so hard to beat? a. The HIV virus can survive harsh conditions for years as a dormant particle. b. The HIV virus has an extremely high rate of mutation. c. The HIV virus replicates its genome with a great deal of precision (i.e., has a low mutation rate). d. The HIV virus has a special protein coat that protects it from attack by all known human immune defenses.

b. The HIV virus has an extremely high rate of mutation.

Suppose there is a population of 100 rabbits. In this population, 60 rabbits are FF, 20 are Ff, and 20 are ff. What is the allele frequency for the F allele in this population's gene pool? a. 0.5 b. 0.6 c. 0.7 d. 0.8

c. 0.7 --> There are 100 rabbits in the population, each with two alleles for the fur color gene, for a total of 200 alleles in the gene pool. Since there are 60 FF rabbits, there are 60 ×× 2 = 120 F alleles from these rabbits. Since there are 20 Ff rabbits, there are 20 ×× 1 = 20 F alleles from these rabbits. (There are zero F alleles from the 20 ff rabbits.) This gives a total of 120 + 20 = 140 F alleles in the gene pool. Since the gene pool has 200 total alleles, the allele frequency for the F allele is 140 / 200 = 0.7.

Which statement regarding natural selection is false? a. Natural selection can be observed working in organisms alive today. b. Natural selection and evolutionary change can occur in a short period of time (a few generations). c. Natural selection starts with the creation of new alleles that are directed toward improving an organism's fitness. d. Natural selection depends on the local environment at the current time.

c. Natural selection starts with the creation of new alleles that are directed toward improving an organism's fitness.

Natural selection is best described as _____. a. a creative force that efficiently develops the best and simplest solutions for all problems in nature b. a forward-looking process that anticipates future problems and designs the necessary tools to solve them through mutation c. a filtering process that fine-tunes the traits of populations by sorting among existing, randomly produced variations d. a completely random and unpredictable process of change, or evolution

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

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? a. According to the Hardy-Weinberg equilibrium, the ratios will not change. b. As the sand-colored fish are eaten, more will be produced to keep their frequency at 90%. c. The proportion of mottled fish will increase over time. d. There is no way to guess the result, because evolution occurs at random.

c. 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.

A dog breeder wishes to develop a breed that does not bark. She starts with a diverse mixture of dogs. Generation after generation, she allows only the quietest dogs to breed. After 30 years of work she has a new breed of dog with interesting traits, but on average, the dogs still bark at about the same rate as other dog breeds. A logical explanation for her failure might be a. the selection was artificial, not natural, so it did not produce evolutionary change. b. quiet dogs have fewer pups than barkers. c. the tendency to bark is not a heritable trait. d. there is a great deal of variation for the trait (barking).

c. the tendency to bark is not a heritable trait

Which term represents the frequency of heterozygotes in a population that is in Hardy-Weinberg equilibrium? a. q b. p c. q^2 d. 2pq

d. 2pq

As proposed by Darwin, what sorts of traits are favored by natural selection? a. Any traits that are produced by mutation and can be inherited. b. Traits that reduce the number of offspring an individual produces, thus helping to reduce the struggle for existence in the next generation. c. Traits that reduce the mutation rate and cut down on unnecessary variation within populations. d. Heritable traits that help individuals survive and reproduce more successfully than others in the same population.

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

If a population is in Hardy-Weinberg equilibrium and remains in equilibrium, which of the following will be true? a. The relative frequencies of three genotypes (AA, Aa, aa) will gradually become stabilized at 1:1:1. b. The dominant allele will take over. c. The population organisms will evolve. d. Individuals survive and reproduce equally well regardless of their genotype.

d. Individuals survive and reproduce equally well regardless of their genotype. --> Absence of selection is a condition of Hardy- Weinberg equilibrium.

When they were first sold, certain insecticides were highly effective in killing mosquitoes. Today, dozens of mosquito generations later, a much smaller proportion of these insects die when sprayed with the same chemicals. Fewer insects are killed today because __________. a. mosquitoes are deliberately adapting themselves to this man-made change in the environment b. the original spraying has caused a permanent mutation, giving the insects genetic resistance to the spray c. mosquitoes that survive spraying develop an immunity to the insecticide d. many mosquitoes today are descendants of mosquitoes with insecticide-resistant characteristics

d. many mosquitoes today are descendants of mosquitoes with insecticide-resistant characteristics --> Individuals whose characteristics give them the greatest chances of survival, such as pesticide resistance, are likely to leave more offspring than are more poorly adapted individuals. This unequal ability of individuals to survive and reproduce will lead to a gradual change in a population, with favorable characteristics accumulating over the generations.

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

diversity

The wing of a bat is homologous to the _____ of a whale. a. rib cage b. blowhole c. tail d. baleen e. flipper

e. flipper