Why do obligate symbionts often contain lower G+C content when compared to free-living organisms?
A) Ancestral symbionts had low GC content genomes by chance, and these low GC content genomes are passed onto their progeny.
B) Free-living organisms must have a more stable genome to survive; low G+C content organisms are often selected against in nature.
C) Replicating high G+C content genomes requires several additional enzymes, to break apart the strong triple bonds formed from GC pairs, which are rarely found in symbionts with relatively small genome sizes.
D) Symbionts usually do not have as many DNA repair mechanisms as free-living organisms, and two common spontaneous mutations change GC pairs into AT pairs.
Answer: D
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A PCR procedure that allows a determination of the amount of a particular DNA fragment that is present in a sample is called
A. reverse PCR. B. real-time PCR. C. quantitative PCR. D. analytical PCR.
Can two different species that are members of the same clade have more than one common ancestor? Choose the MOST correct answer and explanation.
A. No. Because they are members of a clade, by definition they can have only one common ancestor. B. Maybe. Two species in the same clade can have more than one common ancestor only in cases where horizontal gene transfer from a third, previously unrelated, species has occurred. C. Maybe. If they are members of a paraphyletic clade, they can have more than one common ancestor. D. Yes. Although two species in the same clade have only one most recent common ancestor, they also have a number of older common ancestors that occurred earlier in their evolutionary history. E. Yes. Two species of the same clade always have eight common ancestors, matching the number of levels higher than species in the taxonomic hierarchy.
You find some rather strange plants in your backyard. They consist only of thin, pale yellow stems that are wrapped around other species of plants growing nearby. You experiment by unwrapping some of the strange yellow plants and planting half of them alone in pots of soil and half in pots with other plants from your yard. You water and fertilize both sets of pots, but after a few weeks you find that the yellow plants that were potted alone have died, while those potted with other plants are thriving. What term would you use to describe the strange yellow plants?
A. asexual B. holoparasitic C. monophagous D. aposematic E. hemiparasitic
Seven species extinctions (indicated by horizontal bars) completely eliminate three deep branching clades such as in Figure A below
What is the likely impact of such extinctions on the diversity of physiological traits when compared to a case when the same number of extinctions is spread evenly across different clades (Figure B)? a. It affects the same number of species, therefore the effect on physiological diversity is the same. b. Physiological diversity is always greater within than between clades. The extinctions in Figure B will cause a greater loss of physiological diversity. c. Deep branching points correspond to greater evolutionary differentiation. This is also the case for physiological traits. The extinctions in Figure A will have the greater effect. d. All of the above are equally likely.