Do all P-elements encode their own transposase, or just the 2.9 kb element?
The 2.9 kb element is the entire, wildtype P-element found in P strains and encodes transposase gene. It’s like Ac in maize. There are crippled versions, which arise through imprecise excision of the P element, are less than 2.9 kb and cannot themselves move. They are like Ds in maize. Engineered P-elements, for making transgenic flies, can be larger than 2.9 kb but do not usually have functional transposase. V.
