Most alleles of the Drosophila cut (ct) gene are stable. For example, all progeny from crossing ct1 to ct2 to yield ct1 /ct2 heterozygotes have "cut" wings. ct1 is a strong allele with severe cutting of the wings. ct2 and another allele, ctMR2, are weaker with only moderate cutting of the wings. When ctMR2 homozygotes are crossed to ct1 homozygotes, three kinds of progeny are produced, 95% have a moderate cutting of the wings (as expected for ctMR2 / ct1 ), 2.5% have wild-type wings and 2.5% have more severe cut wings like ct1 homozygotes. a) How do you explain the high frequency of reversion to wild-type? b) How do you explain the high frequency of progeny with the more severe cut phenotype?

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?

Which of the following is not a benefit of genetically modified foods? a.pest-resistant crops b.herbicide-resistant crops c.plants that do not require water?

Which plate boundary causes plates to collide forming mountain ranges, volcanoes, and island arcs? give an example of this type of plate boundary. 2. at which plate boundary do rifts and mid-oceans ridges form? give an example of this type of plate boundary. 3. at which plate boundary do plates slide past each other while moving in opposite directions? give an example of this type of boundary.