In fruit flies, an X-linked dominant mutant allele of the Notch gene (N) causes Notched wings in heterozygous females but is lethal in hemizygous or homozygous condition. What ratio of offspring would be observed in a cross of a Notched-wing female with a normal male?
A) 1/3 Notched-wing females, 1/3 normal females, 1/3 normal males
B) 1/4 Notched-wing females, 1/4 normal females, 1/4 Notched-wing males, 1/4 normal males
C) 1/2 Notched-wing females, 1/2 normal males
D) 1/2 normal females, 1/2 Notched-wing males
E) 2/3 Notched-wing females, 1/3 normal males
A) 1/3 Notched-wing females, 1/3 normal females, 1/3 normal males
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High productive agricultural soils; long, cold winters; perennials; grazing mammals and burrowing rodents; fires.
A. desert B. savanna C. taiga D. temperate grassland E. tropical rain forest
An outbreak of severe diarrhea occurs in an intensive care wing of a major hospital. As a result, the patients are all screened for colonization and infection by the pathogenic organism. However, not all of the patients identified carrying the organism by phenotypic identification and characte-rization are displaying symptoms of infection. The reason for this discrepancy is:
a. some patients have a stronger immunity to the pathogenic organism. b. the patients who are not displaying symp-toms have been on antibiotics and the or-ganism has mutated and is no longer pa-thogenic. c. the patients are not all infected with the same strain of the organism that is carrying the enteric toxin causing the diarrhea. d. the laboratory has likely misidentified the organisms.
The Earth formed approximately
a. 4600 years ago. b. 1 million years ago. c. 1 billion years ago. d. 4.6 billion years ago.
The walls of the descending limb of the loop of Henle are relatively permeable to sodium. Indicate whether the statement is true or false