IB 150 Exam 3 practice exam

A population of 500 jackrabbits has two alleles, FBand FW, for a locus that codes for fur color. FBFBindividuals have black fur, FBFW individuals have gray fur,FWFWindividuals have white fur. 250 individuals are black, 150 individuals are gray and 100 individuals are white. What are the observed genotype frequencies in this population?

0.50, 0.30, 0.20

A species of seagulls exists as a large number of different populations on separate islands of the Azores archipelago. Both black and white gulls are present. The black-colored seagull is due to a dominant allele (M). Mm and MM individuals are black, and mm individuals are white. During a storm, two males and two females are blown 300 miles West, to an isolated island uninhabited by seagulls. They reproduce and found a new population. They cannot disperse back to the original habitat, nor can any new seagulls cross to the new island. Three of the original colonists were white-colored gulls and one was black. Genotyping shows the single black gull to be heterozygous. What is the frequency of the recessive (m) allele in this new population?

0.875

What causes insecticides (man-made chemicals intended to kill insects) to become less effective over time?

Regular use of an insecticide kills almost all individuals except those with alleles that allow them to tolerate the insecticide.

In which of the following situations would it be impossible for the indicated mechanism to cause divergence between two populations of flowering plants?

Pollinators have no preference for flower color and routinely visit flowers in both populations

How do sexual selection and inbreeding differ?

Sexual selection can change allele frequencies, inbreeding cannot.

If you observe significant deviations in genotype frequencies for ALL genes from Hardy-Weinberg Equilibrium expectations in a population, that result in higher frequencies of homozygotes than expected, what is likely occurring in this population?

There is a lot of inbreeding in this population

If a trait evolves convergently more than once, what is most likely true?

This trait is most likely adaptive

Finches on the Galapagos Islands require food to eat and water to drink. (Apart of the finches question).

When food and water are scarce, some birds may be unable to obtain what they need to survive.

Consider the following graph of body size in a population of insects in 2008 and 2012: what type of selection is depicted?

disruptive

True or false? Natural selection can create variation of a heritable trait within a population if none exists, but only when the trait increases the fitness of individuals with this trait.

false

Species in a polyphyletic grouping likely have ....

many analogous characters that were mistakenly assumed to be shared derived characters

Which of the following statements justifies why mutation is a random process, but evolution by natural selection is a nonrandom process?

mutation is an error that occurs during DNA replication, but selection results from differences in fitness

Depending on their beak size and shape, some finches get nectar from cactus flowers, some eat grubs from bark, some eat small seeds, some eat large nuts. Which statement best describes the interactions among the finches and the food supply?

Finches compete primarily with closely related finches that eat the same kinds of food, and some may die from lack of food.

Consider the following two genetic disorders (descriptions modified from Wikipedia): Huntington's disease is caused by an autosomal dominant allele of a gene called Huntington. It is a degenerative disorder that affects muscle coordination and leads to cognitive decline and dementia. Physical symptoms of this particular variant of Huntington's disease usually begin between 35 and 44 years of age. Tay-Sachs is caused by an autosomal recessive mutation on the HEXA gene. Its most common variant causes a deterioration of mental and physical abilities that usually results in death by the age of four. Using only this information, could either of these genes be in Hardy-Weinberg equilibrium (HWE) in the US population (>300 million people)?

Huntington's could be in HWE, but not Tay-Sachs

Which reproductive isolating mechanism operates after the zygote is formed?

Hybrid sterility

Which answer correctly describes the order of events that can occur during the process of speciation?

reduced gene flow, selection, reproductive isolation

All phenotypic traits of an organism are adaptations.

true

If you want to test your prediction in the preceding question, which of the following data would you need to collect to directly measure the fitness of male guppies in this population?

Count the number of offspring produced by male guppies

Define what a null hypothesis is. What is the null hypothesis for evolution? What is a prediction associated with this null hypothesis that you can test for a population? What kind of data do you need to collect to test this hypothesis?

A null hypothesis describes what would happen if only random processes are at play. The null hypothesis for evolution is that a population is not evolving, because all alleles are equally likely to be passed on, as all individuals are equally likely to reproduce, and pass their alleles on in the same proportions, while mating with a partner of random genotype for the gene under observation. The PREDICTION associated with this null hypothesis is that genotype frequencies will be in Hardy-Weinberg proportions in the next generation, if (and only if) the null hypothesis is true for a given gene in a population.

In which of the following scenarios would you expect allele frequencies in a population to shift dramatically in just one generation?

A severe flood kills 90% of an insect population.

In which of the following scenarios is the rapid fixation of an allele most likely?

A small population of plants that establish themselves on an island previously uninhabited by this plant

What aspect of fitness is NOT represented by the two shown selection pressures in the graphs above?

Ability to produce viable and fertile offspring

Which of the following is NOT a possible outcome of genetic drift over time?

Adaptation

What type of variation in finches is passed from parent to offspring?

All characteristics that are genetically determined.

How did the different beak types first arise in the Galapagos finches?

Changes in the finches' beaks occurred by chance, and when there was a good match between beak structure and available food, those birds had more offspring.

Which of the following is NOT a good explanation for why crocodiles possess a Foramen of Panizza?

Crocodiles inherited this structure from their common ancestor with all other reptiles.

What process or processes listed below can result in allele fixation?

Directional selection

You sequence the gene TTN in a sample of individuals taken from the boxer population, and discover that the genotype frequencies in the boxer populations are as follows, Where 'T' and 't' represent the dominant and the recessive alleles for gene TTN: genotype # of individuals observed T T 154 T t 51 t t 35

I reject the null hypothesis, with a calculated p-value of <0.001

What information do you need to determine if two birds are the same species using the biological species concept?

If they can produce fertile offspring

Inbreeding depression is not observed in species like Mendel's garden peas, where self-fertilization has occurred routinely for many generations. Why not?

Inbreeding exposes deleterious recessive alleles to selection. After many, many generations of inbreeding, deleterious recessive alleles can be lost from the population. Once this occurs, a self-fertilizing population will not exhibit reduced fitness under additional generations of inbreeding.

Imagine a recessive autosomal genetic disorder that causes death before sexual maturity. Which of the following best helps explain why such alleles persist in populations for long periods of time?

Individuals that are carriers of the allele have the same fitness as individuals without the allele

Why does gene flow make speciation by reproductive isolation less likely?

It prevents populations from diverging

Male guppies are quite colorful fish, while female guppies tend to have a tan coloration. Guppies live in pools at the edges of streams that harbor predatory fish that hunt prey by sight. Furthermore, female guppies show a strong preference for male coloration when selecting a mate, while males tend to court and attempt to copulate with any female they encounter in their environment.

Males experience BOTH selection pressures, females experience selection pressure 1

Based on the scenario described at the beginning, and a comparison of the observed number of individuals to the expected number of individuals if the population were in Hardy-Weinberg Equilibrium, which of the following processes is the most likely to be currently acting on this population of boxers?

Non-random mating - positive assortative mating

Based on the data presented in the previous question, what do you know for sure?

One or more of the five violations of Hardy-Weinberg must have been acting on this population within the last generation to cause its genotype frequencies to deviate from Hardy-Weinberg proportions.

Why do the circulatory systems of land vertebrates have separate circuits: one to the lungs and the other to the rest of the body?

The decrease in blood pressure as blood moves through the lungs may prevent efficient circulation to the rest of the body without passing the heart a second time.

What caused populations of birds having different beak shapes and sizes to become distinct species distributed on the various islands?

The finches were quite variable, and those whose features were best suited to the available food supply on each island reproduced most successfully.

In the finch population, what are the primary changes that occur gradually over time?

The proportion of finches having different traits within a population change.

Which of the following describes a phylogenetic constraint?

a developmental pathway in a group of organisms that can be modified by natural selection but that is difficult to reverse

Which process is most likely responsible for the frequency of the deleterious allele to be more common in the boxer population?

genetic drift

Which of the following graphs shows the overall fitness of male guppies with different phenotypes in this environment?

graph b

Rana aurora (red-legged frog) breeds in fast-moving, temporary streams, whereas its relative Rana catesbiana (Bullfrog) breeds in permanent ponds. What is the isolating mechanism between these Species?

habitat isolation

'Maximum parsimony' is a general principle with broad application in science, which states that:

in the absence of additional information, the explanation that makes the least unsupported assumptions is the most likely.

Which of the following (by itself) will NOT change allele frequencies of a single gene within a population?

independent assortment

Prof. Berlocher, a well-known biologist at the University of Illinois who is working on mechanisms of speciation, found two populations of very similar looking flies in the genus Rhagoletis that live side-by-side on the fruits of hawthorn and apple trees in the same geographic area. He would like to test whether these two populations are in fact separate species, that is, they do not mate with each other to produce viable offspring. Taken individually, he notices that each population (apple and hawthorn population tested separately) is in H-W equilibrium. He is planning to test whether flies from both populations combined are in Hardy Weinberg Equilibrium. He points out that if a group of flies sampled from both populations and combined in the analysis is NOT in Hardy Weinberg Equilibrium, this result would be consistent with the two populations representing distinct species. Why can he make this prediction? - Which assumption of the Hardy-Weinberg principle would be completely violated if the two populations are separate biological species?

individuals choose other individuals at random to mate with

Purebred boxers are one of the dog breeds that have an elevated likelihood to suffer from heritable cardiomyopathy (abnormal heart rhythms caused by a pathological ventricle) that can lead to premature death, and is caused by the presence of a recessive allele of the gene TTN, which codes for the protein titin. Titin provides structure, flexibility, and stability to muscle cells. Genetic testing confirms that the deleterious allele responsible for this condition is unusually common in boxers compared to other dog breeds and compared to wolves (wild ancestors of dogs). Which process is most likely responsible for the frequency of the deleterious allele to be very low in ancestral wolf populations?

natural selection

A small population of wolves was reintroduced to southern New Mexico 20 years ago. Within the population at that time were two different alleles (A1 and A2) for a particular gene that affects coat color. A recent analysis shows that there is only one allele (A2) in that population today, after only three generations. Which of the following mechanisms are potential reasons for this observation?

natural selection AND/OR genetic drift

A virus killed most of the seals in the North Sea (e.g., reduced the population from 8000 to 800). What is this an example of?

population bottelneck