Mastering Biology Chapter 21
In the lab, Nachman examined dark mice from two different populations living hundreds of miles apart. The mice looked nearly identical. Their dark color was caused by two different genes. What does this tell you?
- Dark fur color evolved independently on each lava flow - Two completely different mutations in two separate genes can generate the same phenotype - Under very similar conditions, natural selection can favor very similar adaptations - There are at least two genes involved in creating dark mouse fur
What does Dr. Carroll mean when he says, "while mutation is random, natural selection is not"?
- Natural selection favors some mutations - Natural selection acts on traits - Mutations for advantageous traits are more likely to be passed on to the next generation
Identify the four postulates of natural selection
1. Individuals in a population vary in the traits they possess 2. Some trait differences are heritable 3. Individuals in a population vary in the traits they possess 4. Survival and reproductive success are variable among individuals in a population
Mutations are always _______.
A change in an individual's DNA
Guppy Experiment
Can predation result in natural selection for color patterns in guppies? What we know about evolution changes constantly as new observations lead to new hypotheses—and hence to new ways to test our understanding of evolutionary theory. Consider the wild guppies (Poecilia reticulata) that live in pools connected by streams on the Caribbean island of Trinidad. Male guppies have highly varied color patterns, which are controlled by genes that are only expressed in adult males. Female guppies choose males with bright color patterns as mates more often than they choose males with drab coloring. But the bright colors that attract females also make the males more conspicuous to predators. Researchers observed that in pools with few predator species, the benefits of bright colors appear to "win out," and males are more brightly colored than in pools where predation is intense. One guppy predator, the killifish, preys on juvenile guppies that have not yet displayed their adult coloration. Researchers predicted that if guppies with drab colors were transferred to a pool with only killifish, eventually the descendants of these guppies would be more brightly colored (because of the female preference for brightly colored males). To test this prediction, researchers transplanted 200 guppies from pools containing pike-cichlid fish, intense guppy predators, to pools containing killifish, less active predators that prey mainly on juvenile guppies. They tracked the number of bright-colored spots and the total area of those spots on male guppies in each generation. After 22 months (15 generations), researchers compared the color pattern data for the source and transplanted populations. Their data are shown in the bar graphs.
What question did the researchers ask?
Can predation result in selection for color patterns in guppies?
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
The evolution of populations due to chance is
Genetic drift
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 of the following statements is an accurate combination of postulates 1 and 2 of natural selection?
Heritable variation exists for traits among individuals in a population
When dark-colored fur gives mice a 1% competitive advantage and 1% of the population begins with dark fur, in about 1000 years, 95% of the population will have dark fur. Which of the following statements is true?
If dark-colored rock pocket mice had a competitive advantage of 0.1%, it would take longer for 95% of the population to have dark fur
Which of the following would help strengthen the researchers' conclusion?
If no other characteristics differed significantly between the source and transplanted populations
Which of the following statements is an accurate combination of postulates 3 and 4 of natural selection?
Individuals experience differential success in their ability to survive or reproduce due to difference in certain traits
Does the ability of a Mycobacterium tuberculosis cell to infect a new host depend on its drug-resistant phenotype?
No, drug-susceptible cells and drug-resistant cells are equally likely to infect a new host.
What data should you collect in order to test your prediction?
Predation rate on transplanted versus original source guppies, and color patterns of the population over time
What was the researchers' main hypothesis?
Predation results in selection for more drab color patterns in guppies
What conclusion would you draw from the data presented?
Predation results in selection for more drab coloration in pike-cichlid pools
Which of the following statements describes the evolution by natural selection of Mycobacterium tuberculosis bacteria in their new environment?
The drug-resistance trait is an adaptation to the environment in which human hosts are medicated with the antibiotic rifampin
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
A group of small fish live in a lake with a uniformly light-brown sandy bottom. Most of the fish are light brown, but about 10% are mottled. This fish species is often prey for large birds that live on the shore. 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 of what will happen to this fish population?
The proportion of mottled fish will increase over time
What was the control group in this study?
The source population in the pike-cichlid pools
What was the experimental group in this study?
The transplanted population in the killifish pools
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
Suppose that after 22 months, guppies from the transplanted population were returned to the source pool. What would most likely happen to those guppies?
They would experience a higher rate of predation than the native population, and over time they would evolve and resemble the original source population
How did the types of data the researchers collected enable them to test their prediction?
Tracking the number and area of colored spots provided a quantitative way to compare the brightness of different populations
A farmer uses triazine herbicide to control pigweed in his field. For the first few years, the triazine works well and almost all the pigweed dies; but after several years, the farmer sees more and more pigweed. Which of these statements explains why the pigweed reappeared?
Triazine-resistant weeds were more likely to survive and reproduce
True of false? It would be difficult to assess whether the drug-susceptible or drug-resistant phenotype in a population of Mycobacterium tuberculosis was more fit in an environment without antibiotics
True
Researchers further hypothesized that if predation pressure is reduced, drab coloration would become less beneficial (since females prefer brightly colored mates). Based on this hypothesis, what prediction did the researchers test in this experiment?
When guppies with drab colors are transferred to a pool with only killifish, the transplanted population will evolve brighter colors than the original source population
In a population with brown and green alleles for color, genetic drift
has more effect on the evolution of a small population
