Why does it take more than a week before a mosquito just infected with yellow fever virus can transmit the disease?
A. The virus must replicate in the gut of the mosquito before it can reach high enough numbers for transmission to a new human.
B. Mosquitoes only feed once a week, which limits their ability to transmit the disease rapidly.
C. Yellow fever is caused by a protozoan. It must develop from the sporozoite form into the mature form to become infectious, and this takes time.
D. The virus multiplies in the gut of the mosquito, but then needs to migrate to the proboscis (biting nose) of the animal in order to infect a new human being after a new bite. This migration takes time
A.
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If an operon is regulated by ____ control, genes are ____ by a regulatory protein called a ____
a. positive; on unless they are switched off; repressor b. negative; off unless they are switched on; repressor c. negative; on unless they are switched off; repressor d. positive; off unless they are switched on; repressor e. positive; on unless they are switched off; activator
What type of tissue is blood?
a. epithelial b. muscular c. connective d. adipose e. noncellular fluid
The female gametophyte is the
a. flower. b. ovule. c. embryo sac. d. carpel. e. ovary
Two pure-breeding mutant plants produce white flowers. When they are crossed, all of the progeny have wild-type purple flowers. What does this genetic complementation tell you?
A) The genes are part of distinct biosynthetic pathways. B) The two lines exhibit different mutations in the same gene. C) More than one gene is involved in determining the phenotype. D) The allele is pleiotropic. E) The allele exhibits incomplete dominance.