I don’t know how rare this phenomenon is, but I have never seen one in many decades of butterfly-watching. I do have a vague recollection of a gynandromorph Silver-studded Blue on UKB some time ago.
The raised abdomen seems more indicative of a female pose although the shape suggests male.
What actually happens to cause such genetic mutations? This may be a rather rhetorical question, perhaps quite topical given the ability of viruses to mutate. I know very little about the subject (as my comments demonstrate), but the evolution of prokaryotes into eukaryotes appears to be a result of an incredibly rare freak mutation that happened only once in a billion years or so. Which led eventually to complex organisms like us posting on UK Butterflies. No wonder that SETI and the like are still searching.
