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Antibiotics interfere with prokaryotic cell functions. Streptomycin is an antibiotic that affects the small ribosomal subunit in prokaryotes. Specifically, streptomycin interferes with the proper binding of tRNA to mRNA in prokaryotic ribosomes. Which of the following best predicts the most direct effect of exposing prokaryotic cells to streptomycin?

Researchers studying the evolutionary relationships of three species of snails collected the data shown in Table 1. Table 1. Comparison of selected characteristics of three snail species Species A Species B Species C Location of Fossils North America North America Europe Shell Orientation Counterclockwise Counterclockwise Clockwise Shell Composition Calcium carbonate Calcium carbonate Calcium carbonate Trophic Level Carnivore Carnivore Detritivore DNA Analysis % A+T = 43.2 % A+T = 43.4 % A+T = 43.0 % G+C = 56.8 % G+C = 56.6 % G+C = 57.0 Which of the following data sets is most likely to provide reliable information about the evolutionary relationships among these three snail species?

Prairie dogs are small mammals that live in large colonies in burrows in the ground. Prairie dogs that are near their own relatives when a predator approaches are much more likely to issue a warning bark than those that are near unrelated prairie dogs. The prairie dogs that hear a warning bark are more likely to hide in their burrows than to remain above ground. However, the prairie dog that gives the warning bark is putting itself at increased risk of being identified and killed by the predator. Which of the following presents the most likely evolutionary explanation for the behaviors described?

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. Which of the following best describes the likely evolution of the TAS2R38 locus in the gorilla population?

Nondisjunction during meiosis can negatively affect gamete formation. A model showing a possible nondisjunction event and its impact on gamete formation is shown in Figure 1. The first part of the figure shows a cell that has 5 pairs of chromosomes lined up at the equator of the cell. Each chromosome is composed of 2 chromatids. An arrow points to the next part of the figure that shows the same cell with the chromosomes starting to separate. 4 chromosomes and an additional unseparated pair of chromosomes are shown on the left side of the cell. 4 chromosomes are shown on the right side of the cell. Arrows point from the cell to the next part of the figure that shows 2 cells. One of the 2 cells has 6 chromosomes, each composed of a pair of chromatids, all in a single line along the equator of the cell. The other cell has 4 chromosomes, each composed of a pair of chromatids, all in a single line along the equator of the cell. Arrows point from each cell to 2 more cells in the final part of the figure. The 2 cells derived from the cell with 6 chromosomes each have 6 chromosomes. The 2 cells derived from the cell with 4 chromosomes each have 4 chromosomes. These four cells are labeled Gametes. Figure 1. Model of a nondisjunction event Which of the following best describes the most likely impact on an individual produced from fertilization between one of the daughter cells shown and a normal gamete?

Nine percent of a population is homozygous recessive (aa) at a certain locus. Assuming that the population is in Hardy-Weinberg equilibrium, which of the following is closest to the frequency of the recessive allele (a)?

There are two small black, shaded circles on the plate. The one on the left is labeled A and is surrounded by an unshaded circle on the agar. There is also another small black dot next to the circle. The other circle is labeled P and has no other visible change on the agar. A sterile agar plate, I, is streaked with a pure culture of bacteria by means of aseptic techniques. Paper discs treated with the antibiotics Aureomycin (A) and penicillin (P) are placed at opposite sides of the plate, as shown in the diagram above. The plate is examined after a 24-hour incubation period, and a clear ring is discovered around disc A, but not around disc P. Within the clear ring around disc A, a single bacterial colony with physical characteristics like those of the pure culture is observed. A second sterile agar plate, II, is then streaked with this single colony and also incubated with antibiotics. Which of the following would most likely be observed in plate II after 24 hours?

Researchers investigated the habitat preferences of two species of garter snakes, Thamnophis sirtalis and Thamnophis atratus. To create a choice chamber, the researchers built a meshed enclosure and positioned one end of the enclosure at the edge of a small pond. Zone I of the enclosure was located in the water, whereas zone IV of the enclosure was located 2–3 meters away from the water, as represented in the figure below. Snakes inside the enclosure were able to move freely between zones. From left to right, the zones are labeled 4 through 1. The side length of each square is 1 meter. A large semicircular shaded region, labeled “Pond,” completely covers square 1 and a very small part of square 2. The “Pond” region also extends beyond square 1 to the outside of the enclosure. In a series of experiments, the researchers introduced a single snake into zone IV of the enclosure at 7:00 A.M. The researchers recorded the location of the snake at six time points throughout the day. In a related experiment, the researchers introduced two snakes, one of each species, into the enclosure at the same time and observed the location of each of the two snakes at the same six time points as before. The researchers repeated both the one-snake and two-snake experiments using different individual snakes of each species. The results are presented in the table. The title of the table is ZONES MOST FREQUENTLY OCCUPIED BY GARTER SNAKES IN A MESHED ENCLOSURE. The top row contains the column labels, from left to right: column one, Time of Day; column two, Zone Most Frequently Occupied by T. atratus; column three, Zone Most Frequently Occupied by T. sirtalis; column four, Zone Most Frequently Occupied by T. Both species of garter snakes prey on the California newt, Taricha torosa, a small amphibian that produces a potent neurotoxin (TTX) in its skin. However, neither species of garter snake is affected by TTX. The resistance to TTX is associated with mutations in the SCN4A gene. Which of the following best supports a claim that TTX resistance arose independently in T. atratus and T. sirtalis?

Which of the following statements correctly describes a typical trend during the initial stages of succession in a terrestrial ecosystem?

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. The table shows the position in the Nucleotide Sequence for different species. The data are as follows. Human nontaster; 145, G; 785, T; 886, A. Human taster; 145, C; 785, C; 886, G. Bonobo; 145, C; 785, C; 886, G. Chimpanzee; 145, C; 785, C; 886, G. Gorilla; 145, C; 785, C; 886, 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. The TAS2R38 receptor protein has been detected on the surface of cells from individuals who are homozygous for the nontaster allele of the TAS2R38 gene. Which of the following is the most likely effect of the mutations associated with the nontaster allele on TAS2R38 gene expression?