The sickle-cell allele is pleiotropic (that is, it affects more than one phenotypic trait). Specifically, this allele affects oxygen delivery to tissues and affects one's susceptibility to malaria. Under conditions of low atmospheric oxygen availability,
individuals heterozygous for this allele can experience life-threatening sickle-cell "crises." Such individuals remain less susceptible to malaria. Thus, pleiotropic genes/alleles reveal that _____.
A) new advantageous alleles do not arise on demand
B) evolution is limited by historical constraints
C) adaptations are often compromises
D) chance events can affect the evolutionary history of populations
Answer: C
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The accepted method of testing water supplies for the possible presence of pathogens is to determine the presence of
A. Streptococci. B. coliforms. C. Staphylococci. D. Streptomyces.
Which of the following brings amino acids to the ribosomes?
A) ribosomal RNA B) transfer RNA C) messenger RNA D) introns E) exons
On a hot, dry day, plants will close their stomata to conserve water. Under this scenario, what will happen to the rate of photosynthesis and photorespiration?
What will be an ideal response?
This summer, you are returning to the research station in Costa Rica to follow up on the population of butterflies you have been studying. You are disappointed to find that there are fewer this year than last. In fact, at dinner your friends studying frogs and birds are complaining about the same thing. What type of influence do you suspect?
A. A density-dependent effect like environmental disruption B. A density-independent effect like an introduced predator C. A density-dependent effect like an introduced predator D. A density-independent effect like environmental disruption