The genomes of free-living spirochaetes are larger than those living in animal hosts. Why might this be so?
A.
Free-living spirochetes will need genes to code for additional proteins to synthesize or obtain their own food from the environment around them. Parasitic spirochetes obtain nutrients from the animal host, and may not need to move towards those nutrients either.
B. The spirochetes in animal hosts are different species entirely. As different species, they would naturally have smaller genomes.
C. A smaller genome implies simplicity-the spirochetes living in animal hosts have fewer needs, so they need fewer genes.
D. It isn't so-all spirochetes would have the same size genomes, since they're all the same species of microbe.
A
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Natural colonization can happen in all of the following ways except
A. a flock of birds gets blown off course. B. a bird eats a fruit on the mainland and defecates the seed on an island. C. people plant new species on an island. D. lowered sea levels connect two areas previously isolated. E. birds pick up seeds on their feet while wading in mud and drop them elsewhere.
Molecular clocks are based on _____ mutations
A. advantageous B. lethal C. deleterious D. neutral
The fact that nearly everyone on the island of Sardinia has the same X chromosome sequence indicates that the population has experienced
A) mutation. B) natural selection. C) nonrandom mating. D) gene flow.
Cells that possess a nucleus and a membrane system that establishes internal compartments belong in which of the following groups?
A) eukaryotes B) viruses C) Archaea D) Bacteria