I don't know whether this is a myth, but I've run into this in various publications, and a few Egyptians I know personally have confirmed it: that the Egyptians of today and those who lived in the times of the Pharaohs are genetically identical.
Unlike their neighbors. Whatever Mediterranean state you take, the denizens' DNA will attest to all the migrations their country has witnessed over the past 4000 years or so. In Libya, next door to Egypt, the average citizen will have strains of Sub-Saharan, Greek, Roman, and Arab DNA. Sicilians have Norman blood in their veins, and Greeks have Turkish. And so forth. The Egyptians seem to be an exception: they don't mix with others. At least not genetically. Is this true, and if it is, how do they even manage it?
I mean, they fought all those wars with the Nubians; they once had a large population of Hebrew slaves; they lived under Persian, Greek, and Roman occupation - centuries upon centuries; and then there were the Caliphs; and the Brits; and - nothing? Not a trace? How can that be?