Question

P-elements are a type of transposon commonly used in Drosophila (fruit fly) research. A common marker for P-elements is the miniwhite + gene, an engineered version of the white locus. Flies mutant for the natural white have white eyes instead of wild-type red eyes. A miniwhite + gene on a P-element in a white mutant will produce eye pigment, and will act as a dominant marker indicating that the P-element is present. P-elements used for research are nonautonomous, meaning that they do not encode their own transposase. The transposase is supplied using a second locus, where the transposase enzyme is no longer within a transposon and thus is immobilized (meaning that it cannot move itself). For flies with both a nonautonomous P-element and immobilized transposase, the P-element can move within the genome. Question: A researcher is interested in screening for P-elements inserted into a region on chromosome 3. To produce new insertions, she crosses females homozygous for a miniwhite + P-element on the X chromosome with males homozygous for immobilized transposase on chromosome 2. What genotype will the F1 male flies have? (Note that a “+” indicates a wild-type chromosome without the transposase locus or the P {miniwhite +} insertion. The X /Y chromosomes are listed first, followed by the second chromosome.) a) Xtransposase/ Y; P{miniwhite+} /+ b) XP{miniwhite+}/ Y; transposase / + c) YP{miniwhite+}/ X ; transposase / + d) XP{miniwhite+}/ Y; transposase / transposase

Answer 1

ANS: b) XP{miniwhite+}/ Y; transposase / +

Explanation:

According to her experiment for the new insertion production she interested P-elements into a region on chromosome 3. After this the successful insertion she crosses males homozygous for immobilized transposase on chromosome 2 with females homozygous for a miniwhite + P-element on the X chromosome. So according to the above given options only F1 males (XP{miniwhite+}/ Y; transposase / +) genotype will be possible.