Which of the following provides an example of epistasis?
A) Recessive genotypes for each of two genes (aabb) results in an albino corn snake.
B) In rabbits and many other mammals, one genotype (ee) prevents any fur color from developing.
C) In Drosophila (fruit flies), white eyes can be due to an X-linked gene or to a combination of other genes.
D) In cacti, there are several genes for the type of spines.
B
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Which of the following is a difference between the solenoid and zigzag models for the formation of the 30 nm filament?
A. Most of the evidence to date supports the solenoid model, while the zigzag model is unlikely to occur in cells. B. Linker DNA is at the center of the filament in the zigzag model, and on the outside of the filament in the solenoid model. C. The solenoid model is a one-start helix and the zigzag model is a two-start helix. D. The helical pitch in the solenoid model is higher than the helical pitch in the zigzag model. E. The zigzag model occurs in higher eukaryotes such as humans, while the solenoid model occurs in lower eukaryotes such as yeast.
The exchange surfaces of fish gills are arranged as rows of
A. lamellae. B. trachea. C. alveoli. D. parabronchi. E. spiracles.
Vitamin B3 is a precursor of
a. NADH. b. ATP. c. DNA. d. RNA. e. more than one of these.
During the Pleistocene epoch, plant communities changed dynamically in response to:
a. a meteor impact. b. intense grazing pressure. c. competition with gymnosperms. d. iridium in the soil. e. fluctuating climates (ice ages).