Author: Anonymous

Tay-Sachs disease is a rare inherited disorder caused by an autosomal recessive allele of the HEXA gene. Affected individuals exhibit severe neurological symptoms and do not survive to reproductive age. Individuals who inherit one copy of the allele (Tay-Sachs carriers) typically show no symptoms of the disorder. The frequencies of Tay-Sachs carriers in the general population of North America and in three different subpopulations are presented in the table. For general population the frequency is 0.004. For subpopulation 1 the frequency is 0.037. For subpopulation 2 the frequency is 0.035. For subpopulation 3 the frequency is 0.020. Based on the information presented, which of the following best explains the difference in phenotype between Tay-Sachs carriers and homozygous recessive individuals?

The first figure is labeled crossing over, and depicts a circle with two sets of chromosomes. The first set of chromosomes overlap in two places. The second set of chromosomes overlap in one place. The second figure is labeled conjugation, and depicts two ovals attached to each other by a thin line. The third figure is titled fertilization, and depicts a circular shape surrounded by numerous sperm shapes, all heading toward the circle. The processes illustrated in the models depicted above all result in which of the following?

Arsenic is a toxic element found in both aquatic and terrestrial environments. Scientists have found genes that allow bacteria to remove arsenic from their cytoplasm. Arsenic enters cells as arsenate that must be converted to arsenite to leave cells. Figure 1 provides a summary of the arsenic resistance genes found in the operons of three different bacteria. E. coli R773 is found in environments with low arsenic levels. Herminiimonas arsenicoxydans and Ochrobactrum tritici are both found in arsenic‑rich environments. E. coli, Herminiimonas arsenicoxydans, and Ochrobactrum tritici. One operon for arsenic removal is located on E. coli plasmid R 7 7 3, and it contains, from left to right, the following genes: a r s R, then a r s D, then a r s A, then a r s B, and finally a r s C. The following bacteria are found in arsenic rich environments. Herminiimonas arsenicoxydans contains four operons for arsenic removal. The first operon shown contains, from left to right, the following genes: a r s R, then a r s C a, then a r s B 1, then a r s H. The second operon shown contains, from left to right, the following genes: a r s R, then a r s C a, then a r s B 1, then a r s C b, then a r s H, then Permease. The third operon shown contains, from left to right, the following genes: a r s R, then a r s C a, then a c r 3, then M S F, then a r s C b, then a r s H. The fourth operon shown contains, from left to right, the following genes: a r s R, then a r s C a, then a r s H. Ochrobactrum tritici contains two operons for arsenic removal. The first operon shown contains, from left to right, the following genes: a r s R 1, then a r s D, then a r s A, then C B S, then a r s B. The second operon shown contains, from left to right, the following genes: a r s R 2, then a r s C 1, then a c r 3, then a r s C 2, then a r s H, then a r s R 3. Figure 1. Operons found in three selected bacteria for arsenic removal Researchers claim that bacteria that live in environments heavily contaminated with arsenic are more efficient at processing arsenic into arsenite and removing this toxin from their cells. Justify this claim based on the evidence shown in Figure 1.

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?