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Chapter 13 & 14 13 :Natural Selection and Adaptation: Bugs that Resist Drugs 14: Nonadaptive Evolution and Speciation: Urban Evolution
Terms in this set (28)
A chemical that can slow or stop the growth of bacteria; many antibiotics are produced by living organisms.
The process by which bacteria can exchange segments of DNA between them.
Change in allele frequencies in a population over time.
The relative ability of an organism to survive and reproduce in a particular environment.
Differential survival and reproduction of individuals in response to environmental pressure that leads to change in allele frequencies in a population over time.
The process by which populations become better suited to their environment as a result of natural selection.
Explain two ways that antibiotics kill bacteria.
They work by interfering with a bacterium's ability to synthesize cell walls
Genetic diversity is key to the success of populations. How do bacteria generate diversity within their populations?
Bacterial populations can acquire genetic variation by both mutation and gene transfer—the direct exchange of DNA between bacterial cells. Genetic variation in a population gives rise to corresponding phenotypic variation in the population. Individuals with different phenotypes will have differing ability to survive and reproduce in a population; that is, they will have different fitness.
How do natural selection and adaptation relate to one another?
Over time, natural selection leads to adaptation: advantageous traits become more common in the population, which as a result becomes more suited, or adapted, to its environment.
How do the patterns of natural selection (directional, stabilizing, disruptive) differ from one another?
When the environment favors an extreme phenotype, causing the population to shift in one direction over time, directional selection. The emergence of antibiotic-resistant bacterial populations is a good example of directional selection. When the environment favors the middle of the phenotypic spectrum, and extremes are selected against, we call this stabilizing selection.Human birth weight is an example. Both very small and very large babies are less fit than medium-size babies, who are hearty but still small enough to fit through the birth canal.when the environment favors the ends of a phenotypic spectrum, diversifying selection occurs. An example is finches in environments where only large seeds and small seeds are available; birds with medium-size beaks are not as successful at cracking either type of seed, and so big-beaked birds and small-beaked birds have the advantage
The relative proportion of an allele in a population.
The total collection of alleles in a population.
Any change in allele frequency that does not by itself lead a population to become more adapted to its environment; the mechanisms of nonadaptive evolution are mutation, genetic drift, and gene flow.
Random changes in the allele frequencies of a population between generations; genetic drift tends to have more dramatic effects in smaller populations than in larger ones.
A type of genetic drift in which a small number of individuals leaves one population and establishes a new population, resulting in lower genetic diversity than in the original population.
A type of genetic drift that occurs when a population is suddenly reduced to a small number of individuals, and as a result alleles are lost from the population.
The movement of alleles from one population to another, which may increase the genetic diversity of a population.
Mating between closely related individuals. Inbreeding does not change the allele frequency within a population, but it does increase the proportion of homozygous individuals to heterozygotes.
The genetic divergence of populations, leading over time to reproductive isolation and the formation of new species.
How do we know if evolution has occurred in a population?
if a particular allele for a gene is present 50 times out of a total of 1,000 alleles, its allele frequency is 0.05. Over time, several forces can change the frequency of alleles—that is, how common they are in the population. When the frequency of alleles changes over time, a population evolves.
Your textbook describes two ways genetic drift can occur. Summarize those processes. In class, we'll learn about a third way -meiosis. a.What do both types of genetic drift have in common?
The founder effect is a type of genetic drift in which a small number of individuals establishes a new population in a new location, with reduced genetic diversity as a likely result.
The bottleneck effect is a type of genetic drift that occurs when the size of a population is reduced, often by a natural disaster, and the genetic diversity of the remaining population is reduced.
What effect does gene flow have on populations?
Gene flow is the movement of alleles between different populations of the same species, often resulting in increased genetic diversity of a population.
How does gene flow differ from genetic drift?
"Genetic drift is a bit like rolling the evolutionary dice. By simple chance, some individuals survive and reproduce, and others do not." Those that pass on their genes aren't necessarily more fit or better adapted; they're just lucky—perhaps their nest or burrow wasn't swept away in a flash flood, for example. gene flow, in which alleles move between populations as individuals leave and enter populations and breed with members of other populations. Like genetic drift, gene flow is a type of nonadaptive evolution that does not lead to a population becoming more adapted to its environment. Unlike genetic drift, gene flow tends to increase the genetic diversity of a population, not decrease it
What is one process that can lead to inbreeding?
One reason gene flow is important is that small, isolated populations can be damaged by lack of genetic diversity. Take the Florida panther (Puma concolor), for example. In the past, Florida panthers mated with puma populations from neighboring states where their ranges overlapped. This interbreeding—breeding among different populations of the same species—fostered an exchange of alleles that continually enriched the local populations' genetic diversity. By the mid-20th century, however, hunting and development had squeezed the Florida panther population into an isolated region at the state's southernmost tip. By 1967, only 30 panthers remained, and the U.S. Fish and Wildlife Service listed them as endangered. By 1980, the panthers showed unmistakable signs of ill health—birth defects, low sperm count, missing testes, and bent tails—that resulted from inbreeding, mating between closely related members of a population.
How does natural selection differ from the forces of evolution?
What effect do the forces of evolution have on genetic diversity? Explain why.
Many genetic differences still exist among the local populations of urbanized mice. That's because mutation, drift, and gene flow continue to occur even as natural selection is happening. In fact, for most natural populations, all four mechanisms of evolution—natural selection, mutation, gene flow, and genetic drift—are continually operating at the same time, fostering unique evolutionary outcomes
How can reproductive isolation lead to changes within populations?
Members of different species cannot mate and produce fertile offspring with each other because their populations are reproductively isolated. Such reproductive isolation can be caused by a number of factors. For example, the two species may have different mating times, locations, or mating rituals—so, like ships passing in the night, they may never meet. This is true of many ant species, for example, which breed at different times of year. Or, two species may be able to mate—as zebras and horses can—but the hybrid offspring they produce is infertile
How does microevolution differ from speciation?
Microevolution involves evolutionary changes within a population; speciation occurs when a population changes enough that it diverges from its parent species and becomes a new species.
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