HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR.

HIV's genome of RNA includes the code for reverse transcriptase (RT), an enzyme that acts early in infection to synthesize a DNA genome off of an RNA template. The HIV genome also codes for protease (PR), an enzyme that acts later in infection by cutting long viral polyproteins into smaller, functional proteins. Both RT and PR represent potential targets for antiretroviral drugs. Drugs called nucleoside analogs (NA) act against RT, whereas drugs called protease inhibitors (PI) act against PR. 

Which of the following represents the treatment option most likely to avoid the production of drug-resistant HIV (assuming no drug interactions or side effects)? A) using a series of NAs, one at a time, and changed about once a week 

B) using a single PI, but slowly increasing the dosage over the course of a week
C) using high doses of NA and a PI at the same time for a period not to exceed one day
D) using moderate doses of NA and two different PIs at the same time for several months


Answer: D

Within the body of an HIV-infected individual who is being treated with a single NA, and whose HIV particles are currently vulnerable to this NA, which of these situations can increase the virus' relative fitness? 1. mutations resulting in RTs with decreased rates of nucleotide mismatch 

2. mutations resulting in RTs with increased rates of nucleotide mismatch
3. mutations resulting in RTs that have proofreading capability
A) 1 only
B) 2 only
C) 3 only
D) 1 and 3
E) 2 and 3


Answer: B

HIV has nine genes in its RNA genome. Every HIV particle contains two RNA molecules, and each molecule contains all nine genes. If, for some reason, the two RNA molecules within a single HIV particle do not have identical sequences, then which of these terms can be applied due to the existence of the nonidentical regions? A) homozygous 

B) gene variability
C) nucleotide variability
D) average heterozygosity
E) All but one of the responses are correct.


Answer: E

Every HIV particle contains two RNA molecules. If two genes from one RNA molecule become detached and then, as a unit, get attached to one end of the other RNA molecule within a single HIV particle, which of these is true? A) There are now fewer genes within the viral particle. 

B) There are now more genes within the viral particle.
C) A point substitution mutation has occurred in the retroviral genome.
D) The retroviral equivalent of crossing over has occurred, no doubt resulting in a heightened positive effect.
E) One of the RNA molecules has experienced gene duplication as the result of translocation.


Answer: E

In a hypothetical population's gene pool, an autosomal gene, which had previously been fixed, undergoes a mutation that introduces a new allele, one inherited according to incomplete dominance. Natural selection then causes stabilizing selection at this locus. Consequently, what should happen over the course of many generations? 

A) The proportions of both types of homozygote should decrease.
B) The proportion of the population that is heterozygous at this locus should remain constant.
C) The population's average heterozygosity should decrease.
D) The two homozygotes should decrease at different rates.


Answer: A

Learn More :

Biology

• The most likely explanation for the high rate of sympatric speciation that apparently existed among the cichlids of Lake Victoria in the past is
• Which of these should decline in hybrid zones where reinforcement is occurring?
• A hybrid zone is properly defined as
• The phenomenon of fusion is likely to occur when, after a period of geographic isolation, two populations meet again and
• The origin of a new plant species by hybridization, coupled with accidents during nuclear division, is an example of
• Beetle pollinators of a particular plant are attracted to its flowers' bright orange color. The beetles not only pollinate the flowers, but they mate while inside of the flowers. A mutant version of the plant with red flowers becomes more common with the passage of time. A particular variant of the beetle prefers the red flowers to the orange flowers. Over time, these two beetle variants diverge from each other to such an extent that interbreeding is no longer possible. What kind of speciation has occurred in this example, and what has driven it?
• Among known plant species, which of these have been the two most commonly occurring phenomena that have led to the origin of new species? 1. allopatric speciation 2. sympatric speciation 3. sexual selection 4. polyploidy
• The difference between geographic isolation and habitat differentiation is the
• Two closely related populations of mice have been separated for many generations by a river. Climatic change causes the river to dry up, thereby bringing the mice populations back into contact in a zone of overlap. Which of the following is not a possible outcome when they meet?
• In a hypothetical situation, a certain species of flea feeds only on pronghorn antelopes. In rangelands of the western United States, pronghorns and cattle often associate with one another. If some of these fleas develop a strong preference for cattle blood and mate only with other fleas that prefer cattle blood, then over time which of these should occur, if the host mammal can be considered as the fleas' habitat? 1. reproductive isolation 2. sympatric speciation 3. habitat isolation 4. prezygotic barriers
• What does the biological species concept use as the primary criterion for determining species boundaries?
• Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. If pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species, then which of these terms is applicable?
• Rocky Mountain juniper (Juniperus scopulorum) and one-seeded juniper (J. monosperma) have overlapping ranges. If pollen grains (which contain sperm cells) from one species are unable to germinate and make pollen tubes on female ovules (which contain egg cells) of the other species, then which of these terms are applicable? 1. sympatric species 2. prezygotic isolation 3. postzygotic isolation 4. allopatric species 5. habitat isolation 6. reduced hybrid fertility
• Dogs (Canis lupus familiaris) and gray wolves (Canis lupus) can interbreed to produce viable, fertile offspring. These species shared a common ancestor recently (in geologic time) and have a high degree of genetic similarity, although their anatomies vary widely. Judging from this evidence, which two species concepts are most likely to place dogs and wolves together into a single species?
• When male horses (stallions) and female donkeys (jennets) mate, they produce a sterile hybrid called a hinny. Hinnies occur much less frequently than do mules, but are just as healthy and robust as mules. Logically, which of the following best accounts for the relative rarity of hinnies, and what kind of prezygotic isolating mechanism is at work here?
• Theoretically, the production of sterile mules by interbreeding between female horses (mares) and male donkeys (jacks) should
• Two species of frogs belonging to the same genus occasionally mate, but the offspring fail to develop and hatch. What is the mechanism for keeping the two frog species separate?
• Rank the following from most general to most specific: 1. gametic isolation 2. reproductive isolating mechanism 3. pollen-stigma incompatibility 4. prezygotic isolating mechanism
• Dog breeders maintain the purity of breeds by keeping dogs of different breeds apart when they are fertile. This kind of isolation is most similar to which of the following reproductive isolating mechanisms?
• You are confronted with a box of preserved grasshoppers of various species that are new to science and have not been described. Your assignment is to separate them into species. There is no accompanying information as to where or when they were collected. Which species concept will you have to use?
• There is still some controversy among biologists about whether Neanderthals should be placed within the same species as modern humans or into a separate species of their own. Most DNA sequence data analyzed so far indicate that there was probably little or no gene flow between Neanderthals and Homo sapiens. Which species concept is most applicable in this example?
• Which of the various species concepts distinguishes two species based on the degree of genetic exchange between their gene pools?
• Which of the following statements about species, as defined by the biological species concept, is (are) correct? I. Biological species are defined by reproductive isolation. II. Biological species are the model used for grouping extinct forms of life. III. The biological species is the largest unit of population in which successful interbreeding is possible.
• What is true of the flightless cormorants of the Galápagos Islands?
• What is true of macroevolution?

Share this

Share on FacebookPlus on Google+