Fruitflies of the P strain have P elements in their genome; fruitflies of the M
ID: 79457 • Letter: F
Question
Fruitflies of the P strain have P elements in their genome; fruitflies of the M strain do not. When a female of the M strain is mated to a male of the P strain, most of the F1 progeny are sterile. Why?
The P strain and the M strain are not the same species. P element excision produces double-stranded breaks that the embryo is unable to repair. P element transposition causes insertional mutagenesis of the embryo's genome. Flies of the M strain do not have their own transposase gene, and cannot activate P element transposition. P elements enter the lytic pathway and erupt from the fly embryo, killing it.Explanation / Answer
Flies of the M strain do not have their own transposase gene, and cannot thus activate P element transposition.
The reason is that the P strain contains numerous copies of the P element that are mobilized in embroyos derived from M eggs.These eggs lack a repressor protein that inhibits P element mobilization. P element transposons reside passively in P strains because they express a repressor that keeps the transposons silent.When P strains are mated with an M strain lacking such a repressor the transposons are mobilized and often integrate into genes required for germ cell formation. This explains the high frequency of sterlity in the offsprings.
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