Question 1

An example of evolution that has been readily observed is

Accepted Answer

The increased resistance of bacteria to antibiotics is a classic example of evolution that has been readily observed. As humans use antibiotics to kill bacteria, some bacteria survive due to natural genetic variation. These surviving bacteria pass on their antibiotic resistance genes to their offspring, leading to a population of bacteria that is now resistant to the once-effective antibiotic. This is a clear example of natural selection driving evolutionary change.

Question 2

Evolutionary changes occur when ________ acts upon populations containing individuals with genetic differences.

Accepted Answer

Natural selection acts upon the genetic variation within populations, leading to evolutionary changes over time. It is the process by which traits that improve survival and reproduction become more common in successive generations.

Question 3

If a given population has 30 RR individuals,10 Rr individuals,and 10 rr individuals,what is the allele frequency of R?

Accepted Answer

The allele frequency of R can be calculated by taking the total number of R alleles and dividing it by the total number of alleles. There are 30 RR individuals (2 R alleles each), 10 Rr individuals (1 R allele each), and 10 rr individuals (0 R alleles). So, there are (30*2) + (10*1) + (10*0) = 70 R alleles. The total number of alleles is 2*(30+10+10) = 100. Therefore, the frequency of R is 70/100 = 0.7.

Question 4

New alleles arise by

Accepted Answer

New alleles arise through mutations, which are random changes in an organism's DNA sequence. Nonrandom mating and allele frequency are both related to how existing alleles are distributed in a population, while genetic drift refers to random fluctuations in allele frequencies in small populations.

Question 5

When robins lay a clutch of more than four eggs,their chicks are often malnourished because they have so many to feed.If the robins lay fewer than four eggs,they may not have any viable offspring.As a result,robins typically lay a clutch of four eggs.This is an example of

Accepted Answer

This is an example of stabilizing selection because the fitness of offspring is favored when the clutch size is of intermediate size, whereas extreme or smaller clutch sizes lead to decreased fitness.

Question 6

Which of the following is NOT a mode of natural selection?

Accepted Answer

There is no such thing as “dormant selection.” The other options, directional selection, disruptive selection, and stabilizing selection, are all recognized modes of natural selection.

Question 7

A gene has two alleles,D and d.The frequency of the D allele is 0.2. What is the frequency of the d allele?

Accepted Answer

The frequency of the d allele is 1 minus the frequency of the D allele, so 1 - 0.2 = 0.8.

Question 8

Jean-Baptiste Lamark proposed that populations evolve when traits acquired during the lifetime of a parent are passed down to offspring.What is wrong with this proposal?

Accepted Answer

Lamarck's proposal does not take into account the fact that only changes in the DNA sequence of an organism can be inherited. Traits acquired throughout life generally do not involve changes in DNA, and therefore cannot be passed down to offspring. Darwin's theory of natural selection, which proposes that beneficial genetic mutations are passed down to offspring, is a more accurate explanation for how populations evolve over time.

Question 9

Alex is a student with Strep throat (caused by a strain of bacterium)who is given a prescription for an antibiotic and is told to take the drug for two weeks.After a week,he feels better and stops taking the drug.Two months later,Alex again shows symptoms of Strep throat and decides to finish the leftover antibiotic rather than going to the doctor again.Two months after that,he develops Strep throat for a third time and returns to the doctor.This time,the antibiotic does not work.The doctor runs a test and discovers that the bacterial strain Alex is carrying is antibiotic resistant.What most likely happened?

Accepted Answer

By stopping the antibiotic treatment early, a small number of the more drug-resistant bacteria would survive and repopulate the throat. Over time, the drug-resistant alleles of the bacteria would become more common, resulting in the third infection being caused by a drug-resistant strain. This is a classic example of how antibiotic resistance can develop through the misuse of antibiotics.

Question 10

Which of the following is true with regard to mutations?

Accepted Answer

Mutations can occur randomly or spontaneously due to errors during DNA replication, exposure to mutagens, etc. Environmental pressures may influence which mutations are beneficial or detrimental for survival, but they do not directly cause mutations to occur. Mutations can occur in any organism regardless of growth rate. A single mutation can result in a new phenotype or trait.

Question 11

The population of a cactus species in a particular area has two to seven spines with an average of four spines per square centimeter of surface area.Cacti with fewer than four spines per square centimeter are more easily eaten by the wild boars thriving in the area.Over time,the population of this cactus species in this area have an average of six spines per square centimeter of surface area.This is an example of

Accepted Answer

The increase in average number of spines suggests a shift towards individuals with more spines, which is an example of directional selection. The cacti with fewer than four spines are being selectively eaten, which is likely driving this directional shift towards individuals with more spines. Disruptive selection would involve favoring extreme values on either end of a trait distribution, and stabilizing selection would involve favoring intermediate values. There is no evidence of genetic drift in this scenario.

Question 12

In natural selection,________ that increase survival and reproductive success become more common in a population.

Accepted Answer

Natural selection operates on phenotypes, or physical traits and behaviors, of individuals within a population. Those phenotypes that provide an advantage in survival and reproduction are more likely to be passed on to the next generation, leading to an increase in their frequency within the population over time. This change in frequencies of beneficial phenotypes is what drives the evolutionary process.

Question 13

Several related bird species live in a desert.One species is much smaller than the other species.This small species nests in holes in cacti.Because the bird is so small,it can easily squeeze between the spines of the cactus and create a well-protected nest.This is an example of

Accepted Answer

The fact that the small bird species is able to create a well-protected nest in the cactus holes demonstrates that this adaptation provides a survival advantage. Over time, individuals with this trait will be more successful at reproducing and passing on this trait to their offspring. This process of differential reproductive success due to advantageous traits is known as natural selection.

Question 14

In a shallow bay,a population of oysters is the food source for the local crabs.The lightest colored oysters blend with the color of the rocks and the darkest colored oysters are concealed in the shadows cast by the rocks.Oysters with an intermediate coloring are easily detected by the crabs and become a tasty meal for them.Over time,fewer and fewer oysters display the intermediate coloring while more oysters are either the lightest coloring or the darkest coloring.This is an example of

Accepted Answer

This is an example of disruptive selection, as individuals with intermediate coloring are being selected against and the population is becoming bimodal, dominated by individuals with either the lightest or darkest coloring. Stabilizing selection would result in the opposite outcome, where individuals with intermediate traits would be favored and the population would become more homogeneous. Directional selection would favor individuals with a specific extreme trait, but in this case, both light and dark coloring are being favored. Genetic drift refers to random changes in gene frequencies, which is not the cause of the observed pattern in this scenario.

Question 15

Evolution can be described as

Accepted Answer

Evolution is a gradual and continuous change in the genetic characteristics of a population of organisms over time. This change can result from a variety of factors, including natural selection, genetic drift, and gene flow. Option A is incorrect as evolution does not follow a pre-designed plan. Option B is incorrect as sudden shifts in an individual's genetic characteristics are not sufficient to bring about evolutionary change in a population. Option D is incorrect as isolation can be a factor in evolution, but it is not the definition of evolution itself.

Question 16

What is the total number of alleles present for any given gene in a population of 100 individuals?

Accepted Answer

Each individual carries two alleles for any given gene, so in a population of 100 individuals, there are a total of 200 alleles present.

Question 17

When individuals with intermediate values of an inherited phenotypic trait,like head circumference at birth,have an advantage over other individuals in the population,________ is the apparent pattern of natural selection.

Accepted Answer

Stabilizing selection favors individuals with intermediate phenotypes, often leading to a decrease in population variation for the trait in question without changing the mean of the trait. This is because individuals with extreme values of the trait are selected against, while those with values closer to the population mean are more likely to survive and reproduce.

Question 18

The color of a certain species of beetle is determined by a single gene.Two beetles homozygous for green coloration (meaning they have two copies of the green allele)produce a single offspring with brown coloration.Brown color appeared in this offspring as a result of

Accepted Answer

The appearance of a new trait (brown coloration) in an individual that had two parents with a different color (green) is likely the result of a mutation. This suggests that one of the green alleles in one of the parents underwent a change in its DNA sequence, leading to the production of a brown pigment instead of a green one.

Question 19

Insecticides are used to kill insects.However,insecticide-resistant insects are being found.What is the mechanism for this new insect trait?

Accepted Answer

Insects with a random mutation that allows them to survive exposure to insecticides are more likely to reproduce and pass on the resistant trait to their offspring, leading to the development of insecticide-resistant populations over time. This is known as natural selection.

Question 20

Disruptive selection operates whenever

Accepted Answer

Disruptive selection occurs when extreme traits on either end of the spectrum are favored by natural selection, leading to a split in the population and potentially the development of two separate species. This is in contrast to stabilizing selection which favors intermediate traits and reduces the variation in a population. Option A is incorrect because disruptive selection is not disrupted by genetic drift, but rather operates independently of it. Option B is also incorrect because disruptive selection implies that there is a shift away from a balanced gene pool towards two distinct gene pools. Option C is incorrect because only the survival of the smallest individuals would not result in a split in the population and is not characteristic of disruptive selection.

Quiz 12: Mechanisms of Evolution