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A researcher hypothesizes that RNA molecules were present in the most recent common ancestor of all living Which of the following scientific questions would best test the hypothesis?

The area covered by tropical rain forest is reduced by millions of hectares per year due to agriculture and logging. Which of the following best describes a likely result of tropical rain forest deforestation?

Which of the following communities is likely to be most stable?

Iridium is an element that is rare on Earth but commonly found in meteorites. A scientist believes that the first organic molecules may have come to Earth on meteorites 3.6 billion years ago. Which of these would be an appropriate null hypothesis to test related to whether meteorites hit the Earth 3.6 billion years ago?

Which of the following is most likely to create genetic variation in a population?

The diagram below illustrates the results of electrophoresis of DNA sequences obtained from a family of two adults and three children, and amplified using PCR. The bands represent short repeating sequences of variable length. Results for another female (X) are included for comparison. Beginning with the origin there are six lengths of DNA fragments that have separated on the gel. For each fragment the individual that has a band at that basepair length on their gel will be listed. The largest fragment, fragment one: father, child one. Fragment two: child three. Fragment three: mother, child one, child two, X. Fragment four: X. Fragment five: father, child two, child three. Fragment six: mother. The banding patterns of the DNA fragments reveal that

Figure 1 represents part of a process essential to gene expression. The two strands of the helix are paired at each end but are separated in the central portion. Bases of the nucleotides are indicated for the entire length of each strand. The left end of the upper strand is labeled 5 prime, and the right end is labeled 3 prime. The left end of the lower strand is labeled 3 prime, and the right end is labeled 5 prime. The lower strand is also labeled Strand X. An additional single strand of nucleotides that is complementary to the lower DNA strand is also present on the left and central portions of the figure. The sequence of the strand, from the left 5 prime end to the right 3 prime end, is as follows: A U G C C G C A A U C U G U U C A C G C A C U C A U G U G. Above the strand an arrow labeled Direction of Synthesis points along the strand from left to right. Figure 1. Model of process involved in gene expression. Which of the following best explains what strand X represents?

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.