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Cells that contain only circular chromosomes are most probably which of the following?

Fur color is a genetically controlled trait in mice. A population of a species of mouse that typically lives in habitats with light-colored soil was studied for several generations. The background color of the habitat of this population became darker after the second generation due to human activity. A researcher sampled approximately 120 mice in each generation and recorded the fur color phenotypes as shown in Figure 1. The categories are labeled along the horizontal axis as First Generation through Fourth generation. Each category has two bars indicated on it, which are each labeled Light-colored fur and Dark-colored fur, respectively. Each bar has an error range indicated. The vertical axis is labeled Number of Mice, and the numbers 0 through 120, in increments of 20, are indicated. The data for each bar is presented as follows. Note that all values are approximate. First Generation. Light-colored fur, 100, plus or minus 8. Dark-colored fur, 20, plus or minus 8. Second Generation. Light-colored fur, 91, plus or minus 16. Dark-colored fur, 30, plus or minus 10. Third Generation. Light-colored fur, 60, plus or minus 8. Dark-colored fur, 60, plus or minus 8. Fourth Generation. Light-colored fur, 20, plus or minus 4. Dark-colored fur, 100, plus or minus 8. Figure 1. Fur color phenotype distribution of mice over four generations The researcher claims that there is no selective advantage to fur color, so light and dark fur color phenotypes are present in similar frequencies in the fourth generation of this mouse population. Based on the data in Figure 1, which of the following best evaluates this null hypothesis?

Scientists have found that the existing populations of a certain species of amphibian are small in number, lacking in genetic diversity, and separated from each other by wide areas of dry land. Which of the following human actions is most likely to improve the long-term survival of the amphibians?

The TAS2R38 gene encodes a receptor protein that influences the ability to taste bitterness. The gene has two alleles: a dominant, wild-type allele that enables an individual (taster) to taste bitterness and a recessive, mutant allele that interferes with the ability of an individual (nontaster) to taste bitterness. Three single nucleotide mutations in the coding region of the TAS2R38 gene are associated with the nontaster allele. The nucleotides present at the three positions are shown in the table below. Nucleotide Variation in the TAS2R38 Gene Position in the Nucleotide Sequence 145 785 886 Human nontaster G T A Human taster C C G Bonobo C C G Chimpanzee C C G Gorilla C C G A cladogram representing the evolutionary relatedness of selected primates is shown below. From left to right, the branches are as follows: Orangutan, Gorilla, and Chimpanzee. Past the branches, the main line is labeled Human. Another branch, labeled Bonobo, is connected to the Chimpanzee branch. Toxic substances often have a bitter taste that causes animals who try to eat such substances to spit them out rather than swallow them. Additional data suggest that gorilla populations have a very low frequency of nontasters. In a sample of 2,400 people, 1,482 were found to have the dominant (taster) phenotype. Assuming that the population is in Hardy-Weinberg equilibrium, approximately how many individuals in the sample are expected to be heterozygous for TAS2R38?

labeled from left to right: individual 1, individual 2, individual 3 and individual 4. Starting from the smallest bands at the bottom of the figure, the bands will be numbered from 1 to 50, and if an individual has a band of the same basepair fragment size it will be listed as a thick or thin band and the number of the individual. Band 1, thick band 2, thick band 3. Band 2, thick band 4. Band 3, thin band 4. Band 4, thin band 4. Band 5, thin band 2, thin band 3. Band 6, thin band 4. Band 7, thick band 4. Band 8, thin band 3. Band 9, thick band 1. Band 10, thin band 1, thin band 2. Band 11, thick band 1, thick band 2. Band 12, thick band 2, thick band 3. Band 13, thin band 4. Band 14, thin band 4. Band 15, thin band 3. Band 16, thin band 3. Band 17, thin band 2, thin band 3. Band 18, thin band 1, thin band 2. Band 19, thick band 4. Band 20, thin band 1. Band 21, thin band 4. Band 22, thick band 4. Band 23, thick band 4. Band 24, thin band 2, thin band 3. Band 25, thick band 1, thick band 2. Band 26, thick band 3. Band 27, thick band 2, thick band 3. Band 28, thin band 1. Band 29, thin band 2, thin band 3. Band 30, thin band 3, thin band 4. Band 31, thin band 1, thin band 2. Band 32, thick band 4. Band 33, thin band 1. Band 34, thin band 4. Band 35, thin band 4. Band 36, thin band 1. Band 37, thick band 3, thin band 4. Band 38, thin band 1. Band 39, thick band 1, thick band 2. Band 40, thick band 4. Band 41, thin band 3. Band 42, thick band 1, thick band 2. Band 43, thin band 3. Band 44, thick band 2, thick band 3. Band 45, thick band 1, thick band 2. Band 46, thin band 4. Band 47, thick band 3. Band 48, thin band 4. Band 49, thin band 3. Band 50, thick band 1, thin and 2, thin band 3. Samples of DNA were isolated from four different individuals and each sample was digested by the same restriction enzymes. Gel electrophoresis was used to separate the resulting DNA fragments and the results are show above. These data best support which of the following hypotheses?

The bacterium Vibrio cholerae is harmless unless a lysogenic bacteriophage provides the gene coding for the cholera toxin, which converts the bacterium to the virulent form that causes cholera. Which of the following best explains how the gene encoding cholera toxin becomes part of the bacterial genome?

The three-spined stickleback (Gasterosteus aculeatus) is a small fish found in both marine and freshwater environments. Marine stickleback populations consist mostly of individuals with pronounced pelvic spines, as shown in Figure 1. Individuals in freshwater stickleback populations, on the other hand, typically have reduced pelvic spines, as shown in Figure 2. Each figure shows an image of a stickleback fish with a genetic structure below it. The left figure is labeled Figure 1. Marine stickleback. A long Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. The right figure is labeled Figure 2. Freshwater stickleback. A short Pelvic Spine on the fish is labeled. The genetic structure below the fish contains three enhancers, a promoter, and a gene. From left to right, the Enhancer Sequences are labeled Hindlimb, Pituitary, and Jaw. The Hindlimb enhancer is crossed out with an X, and it is labeled Disabled Due to Mutation. To the right of the Enhancer Sequences is a Promoter with an arrow moving up and to the right, over the top of the Pitx1 gene. As represented in Figure 1 and Figure 2, the phenotypic difference between marine and freshwater sticklebacks involves Pitx1, a gene that influences the formation of the jaw, pituitary gland, and pelvic spine. Enhancer sequences upstream of the Pitx1 genetic locus regulate expression of the Pitx1 gene at the appropriate times and in the appropriate tissues during development. Previous studies have found that a mutation in the hindlimb enhancer interferes with the formation of a pronounced pelvic spine. Which of the following best describes how sticklebacks in the same population with identical copies of the Pitx1 gene can still show phenotypic variation in the pelvic spine character?

Figure 1 illustrates processes related to control of transcription and translation in a cell. Gene X is shown at the top of the diagram, and a vertical arrow extends down from Gene X to a line representing an m R N A, where 5 prime is indicated at the left end and 3 prime is indicated at the right end of the m R N A. An arrowhead is also present at the 3 prime end of the m R N A. Another vertical arrow extends down from the m R N A to a circle labeled Transcription Factor. Five arrows extend from the Transcription Factor to 5 genes, labeled from left to right as Gene A, Gene B, Gene C, Gene D, Gene E. All of the genes except Gene D are labeled on; Gene D is labeled off. Genes A, B, C, and E each have a vertical arrow extending down to a short line representing an m R N A. A vertical arrow extends from each m R N A to a circle. The labels under the circles from left to right are Protein A, Protein B, Protein C, and Protein E. No arrows extend from Gene D. Figure 1. Model of a relationship between a transcription factor and selected genes Which of the following scientific claims is most consistent with the information provided in Figure 1?

In an experiment on the effects of deforestation of a portion of a northern temperate deciduous forest, all the trees were removed from a small mountainside watershed area and herbicides were applied for three years to prevent regrowth. Measurements of the concentration of calcium (an important nutrient) in runoff water were taken both before and after the deforestation. Monthly measurements also were made in a similar watershed in another part of the same forest that had been left undisturbed. The findings are displayed in the graph below. The figure shows a graph in quadrant one titled Monthly Measurements Of Calcium Concentration In Runoff Water. The horizontal axis has every month from June, 1965 to May, 1968, with a tick mark at each month. The vertical axis is labeled calcium ion concentration in runoff water in milligrams per liter, from zero to eleven in increments of one. The time of deforestation is marked at December 1965. There is a dashed line labeled losses from undisturbed watershed that remains at one milligram per liter with only slight fluctuations from June 1965 until the end of the graph in May 1968. There is a solid line labeled losses from disturbed watershed. The calcium ion concentration in runoff water for losses from disturbed watershed is approximately one milligram per liter from June 1965 until May 1966. There is a sharp increase from May to July where the ion concentration reaches seven milligrams per liter, then drops to five in August, and continues rising with fluctuations until October 1966 when it reaches a concentration of nine milligrams per liter. There is a decrease over time, with fluctuations, to six milligrams per liter by May 1967, when the concentration increases rapidly to above eleven, peaking in September 1967, then decreasing steadily with small fluctuations to approximately four milligrams per liter in May 1968. Which of the following is best supported by the data?

In certain Native American groups, albinism due to a homozygous recessive condition in the biochemical pathway for melanin is sometimes seen. If the frequency of the allele for this condition is 0.06, which of the following is closest to the frequency of the dominant allele in this population? (Assume that the population is in Hardy-Weinberg equilibrium.)