Chapter 13

An organism's fitness depends on its _____.

Ability to survive and reproduce

Bacterial Populations DNA

Bacterial populations can acquire genetic variation by both mutation and gene transfer—the direct exchange of DNA between bacterial cells. Within any population, there is genetic variation among individuals. This variation exists in the form of different alleles that arise randomly by mutation. Populations of bacteria exist nearly everywhere, including on and in our bodies; most are harmless or even beneficial, but some can cause disease.

Genetic variation

Genetic variation in a population gives rise to corresponding phenotypic variation in the population. Individuals with different phenotypes will have differing abilities to survive and reproduce in a population; that is, they will have different fitness.

High Fitness

Individuals with higher fitness in a given environment reproduce and pass on their alleles more frequently than do individuals with lower fitness, resulting in evolution by natural selection.

A bacterial cell that is resistant to a particular antibiotic may spend a large amount of energy producing the modified proteins that are needed for resistance. In such a case, what would be the effect on this cell's fitness if no antibiotic was present?

Its fitness would be lower than other strains that lack resistance because it is spending energy that the resistant strains can use for other purposes, such as reproduction.

Natural Selection : Forms/Types

Natural selection can take several forms that shift phenotypes in a population in distinct ways: directional selection, diversifying selection or stabilizing selection. Antibiotic-resistant populations of bacteria emerge by directional selection in the presence of antibiotics.

Natural Selection -- Adaptation

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.

Population

Populations are groups of individuals of the same species living together in the same geographic area Populations of bacteria exist nearly everywhere, including on and in our bodies; most are harmless or even beneficial, but some can cause disease.

Which statement expresses the only way to prevent the evolution of new antibiotic-resistant bacteria?

Stop using antibiotics entirely.

Natural Selection

The differential survival and reproduction of individuals in a population over time in response to environmental pressure is called natural selection. Natural selection is one cause of evolution, which is defined as a change in the allele frequency of a population over time.

Gene Transfer

The direct exchange of DNA between bacterial cells.

If you examine a natural population of bacteria, it is common to find some antibiotic-sensitive and some antibiotic-resistant strains, even if the population has never been exposed to any antibiotic. Which explanation could account for this situation?

The resistant strain developed as a mutation and had no negative effect on fitness.

Which factor may prevent most people from developing more than minor skin blemishes when they have a staph infection?

They are practicing good hygiene, including frequent hand washing. Their immune systems are preventing the infection from spreading. Helpful bacteria on their skin keep staph in check. Their skin is a physical barrier that keeps out the bacteria.

The development and spread of a new gene for antibiotic-resistance in a population of bacteria that are exposed to that antibiotic would mean that trait is a(n)

adaptation

Why is the evolution of antibiotic resistance in bacteria happening so quickly?

because any use of antibiotics will select for resistant bacteria because of overuse of antibiotics in humans because of overuse of antibiotics in livestock because bacteria can reproduce so quickly

Why aren't human populations evolving to produce immune systems that are able to fight off MRSA and other "superbugs"?

because the rate of human evolution is much slower than bacterial evolution

What is the evolutionary process called that causes antibiotic-resistant bacteria to increase and antibiotic-sensitive bacteria to decrease in an environment where antibiotics are present?

natural selection

All of these statements are true regarding S. aureus EXCEPT:

nearly 1% of the U.S. population is colonized with S. .

Which factor is going to affect how natural selection acts on a given group of organisms?

reproductive success of individuals which phenotypes are present survival rate of individuals

Which of these is a pattern of natural selection?

stabilizing selection directional selection diversifying selection

A bacterial cell with which modification might be resistant to antibiotics such as methicillin?

the ability to produce an enzyme that breaks down the antibiotic