Drosophila PP elements were discovered because of a phenomenon called hybrid dysgenesis-sterility of particular hybrid progeny. When scientists in the 1970s1970s crossed their D.D. melanogaster laboratory strains to flies of the same species obtained from natural environments outside the lab, they observed a remarkable result: The progeny of the crosses were sterile, but only when outside males were crossed with lab strain females. Progeny resulting from crosses of outside females with lab males were perfectly normal. DNA analysis revealed that while the genomes of the outside flies contain PP elements, the lab fly genomes have none. Apparently, PP elements spread throughout the wild population of DD. melanogaster after the capture of the originators of present-day laboratory strains over 100 years ago.
C) When males from certain outside strains are
mated to lab females, the hybrid progeny are only partially sterile rather than completely sterile. Given this information, describe crosses that would allow you to isolate loss-of-function mutations in the X-linked Drosophila gene yellow that are caused by PP element insertion. (These recessive mutant alleles will produce yellow rather than the wild-type tan body color.) At the molecular level, what do you think explains the difference between outside strains whose hybrid progeny are all sterile and outside strains whose progeny are only semisterile?
D) In wild-type fruit flies, researchers can observe rare patches on the bodies that have yellow rather than tan color. Interestingly, the frequency of these yellow patches did not increase in the progeny of a cross between outside males and lab females. What property of hybrid dysgenesis does this result suggest?
Please and thank you! (If possible, please no cursive if hand written, I can't read it that well... thank you!)
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