Human triploid and tetraploid fetuses occur, but they are inviable and undergo spontaneous abortion. Any of the following events could produce a polyploid fetus EXCEPT:
A. defective spindle apparatus during early
mitosis.
B. failure of homologous chromosome
separation.
C. fertilization of an egg by more than one
sperm.
D. chromosome duplication without cell
division.
E. development of an unfertilized ovum.
E
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Which of the following is not true of topoisomerase inhibitors?
A. They are effective against cancer cells and are currently used in chemotherapies against colorectal and ovarian cancer. B. They are effective against bacterial infections such as infections by the bacteria that cause anthrax. C. They are highly specific so there is negligible general toxicity and usually no unpleasant side effects associated with anticancer therapies that target topoisomerases. D. The anticancer agents that target topoisomerases generally increase the levels of DNA damage in targeted, rapidly growing tumor cells. E. They inhibit topoisomerases by trapping the topoisomerase-DNA complex in which the DNA is normally cleaved, preventing religation.
Which of the following systems is the first of those listed below to begin development in the human
embryo? a. nervous system b. excretory system c. reproductive system d. skeletal system e. endocrine system
Introducing a foreign piece of DNA into an organism in such a way that it can be passed along through the germ line (eggs and sperm) and hence to subsequent generations creates a ________ organism
Fill in the blank with correct word.
The primary advantage of gills versus the body surface for gas exchange in aquatic animals is that ________.
A. gills are located near the mouth B. gills decrease resistance to movement C. all gills contain a countercurrent exchange system D. gills have a much greater diffusion surface area