Which vertebrate group has a three-chambered heart?
A) Mammals
B) Amphibians
C) Lobe-finned fishes
D) Ray-finned fishes
E) Birds
B
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Which of the following is true?
A) Mutations that inactivate tumor suppressor genes are important in cancer. B) Cancer is a single disease with one underlying molecular cause. C) Uncontrolled cell growth alone is sufficient for the development of cancers. D) Cancer is a single disease resulting from a common set of mutations.
A free-swimming jellyfish has a body form known as a
(a) polyp. (b) strobila. (c) medusa. (d) hydra.
As many as 60% of people in malaria-infected regions of Africa have the sickle-cell allele, but only about 10% of the U.S. population of African ancestry carries the allele. Malaria remains a major disease in central Africa but has not been a serious problem in the U.S. for many generations. What is/are the reason(s) for the difference in the percentages and what is a reasonable statement about future percentages?
A. The presence of malaria in Africa maintains the advantage of the heterozygous sickle-cell trait, and the prevalence of malaria will likely continue to preserve the 60% rate. B. Lack of widespread malaria in the United States would have resulted in both homozygous and heterozygous carriers of sickle cell undergoing several generations of negative selection. We should expect this to continue unless innovative therapies give all individuals an equal chance of surviving and reproducing. C. The U.S. percentage may have always been somewhat lower due to immigration from nonmalaria regions, but changes in sites and rates of immigration could occur. D. All of the choices are reasonable.
What factor(s) typically influence a trait that shows continuous variation?
A) genetic factors only B) environmental factors only C) both genetic and environmental factors D) neither genetic nor environmental factors