DNA sequences that are methylated by a cell are usually genes that:a
have been replicated
b. are actively expressed.
c. are inactive.
d. are constitutive.
e. are repressed.
C
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The difference between normal and sickle-cell hemoglobin is _____
a. the number of amino acids in the molecule b. the substitution of one amino acid for another c. the number and orientation of the amino acid chains attached to the heme portion of the molecule d. the number of oxygen molecules that can be carried e. the types of blood cells that produce each protein
Which of the following is a gastropod?
a. clam. b. snail. c. squid. d. octopus.
One of the drawbacks to using pheromones for communication is:
a. they are effective only at night. b. they can only affect unrelated species. c. they are toxic to unrelated species. d. they require little energy for production. e. they can transmit only a limited amount of information.
Ritalin, like cocaine and amphetamines, acts by increasing the concentration of which neurotransmitter in neuronal synapses?
A) dopamine B) serotonin C) acetylcholine D) gamma-aminobutyric acid (GABA)