Without getting into the very many other issues that come to mind, I have to observe, first of all, that "genetics" cannot possibly have anything to do with this.

Not that a person's genetic heritage might not impact their musical inclinations and talents ~ I'm sure that it always does. But I don't see how any meaningful difference could ever be found between the genetic makeup of the black folks who wound up living in the Delta area, as opposed to those anywhere else in the South, or for that matter anywhere else in the US, or even beyond.

The Delta was sort of the "Wild West" of the world of American slavery, occupied and developed long after the plantation system had been founded to grow tobacco, rice and indigo in coastal Virginia/Carolina/Georgia. The very large Black population harnessed to work the industrial-scale cotton operations that emerged later along the Mississipppi did not come directly from Africa, or even from the Caribbean ~ most came from slave states further to the east.

So, their genetic characteristics, as a group, couldn't possibly be significantly different from those of other African Americans.

Incidentally, some of you reading this may not know that the "Mississippi Delta" is nowhere near the mouth of the river. This term actually describes the northwest corner of the state of Mississippi, just south of Memphis, Tennessee. The once-very-fertile land of the area, wen first discovered, was especially rich in silt from the river's annual flooding over eons of geological time.

The geographical term "delta" refers to the silt deposis typically built up around its mouth; in the case of the Mississippi, the land on either bank for almost half its length ~ the southern portion ~ is alluvial silt. The cotton-growing region just below Memphis became known as "The Delta" because the characteritically fertile soil covered an unusually wide region there.

Technically, I suppose, the word "delta" could be used for an even larger area on either side of the river, much of Arkansas and Mississippi and at least half of Louisiana. But, in practice and by custom, the term "Mississippi Delta" refers to a well-defined region of northwestern Mississippi.