Characterize the frequency of changes in chromosome number in humans
A. Close to half of all conceptions are aneuploid.
B. They are a major cause of reproductive failure.
C. The frequency is significantly higher than it is in closely-related animals.
D. All of these.
E. None of these.
D
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The sense of euphoria from low doses of barbiturates is chiefly due to __________.
A. an inhibition of the respiratory centers in the medulla B. a disinhibition of the cerebral cortex C. an inhibition of the reticular formation D. an excitation of the limbic system
Alternate forms (the DNA sequences indicated by alphabetic abbreviations) of the same gene are called
a. traits. b. chromatids. c. chromosomes. d. centromeres. e. alleles.
The reptiles, which include lizards, snakes, alligators, crocodiles, turtles, and birds, evolved from the _____.
A) reptiles. B) amphibians. C) vertebrates. D) both A and C E) both B and C
At about what point in gestation can an ultrasound exam determine the sex of the fetus?
A) about 4 weeks after fertilization B) at the end of the first trimester C) about 20 weeks after fertilization D) at the end of the second trimester