A man with trisomy 21 could pass Down syndrome to offspring if he
A) produces sperm that have two copies of chromosome 21.
B) produces sperm lacking chromosome 21.
C) also has Turner syndrome.
D) is a carrier of a deletion for chromosome 21.
A) produces sperm that have two copies of chromosome 21.
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There are little birds that spend a great deal of time on the back of a rhinoceros and eat the blood-sucking ticks out of the rhino's ears. The rhino greatly benefits from the relationship, since it cannot remove the ticks itself. The tick-rhino relationship is an example of ________.
A. mutualism B. predator-prey C. commensalism D. parasitism
At rest, neurons exhibit a negative membrane potential. Among the factors that maintain this polarity, assess which is most DIRECTLY responsible for the difference between intracellular and extracellular ion concentrations?
A. movements of negatively charged proteins and nucleic acids across the membrane. B. passive leakage of Na+ ions across the membrane. C. passive leakage of K+ ions across the membrane. D. movement of Na+ ions through voltage-gated Na+ channels. E. movement of K+ ions through voltage-gated K+ channels.
An example of a species that uses the estuary as a nursery ground is the:
a. Atlantic eel. b. seal. c. shad. d. lobster. e. tuna.
The "thumb" of the panda is really a modified ________ bone, which evolved because it improved ______________.
Fill in the blank(s) with the appropriate word(s).