there are two types of DNA, nuclear (this is our main DNA, it is our genetic code), and mitochondrial.
Nuclear DNA is extracted from the nucleus of the cell. It is contained in 46 chromosomes, 22 pairs of autosomes + 2 sex chromosomes, XX or XY.
STR is just a method to analyze DNA. There are others, too. Y STR is just “Y chromosome analyzed by STR”.
STR analysis - Wikipedia
Now, if there is very little material and the sample is halfway destroyed, it potentially could be so that you recovered one Y and nothing else, but highly, highly unlikely.
Y is passed from father to son potentially unaltered, although from one generation to another, there might still be mutations. They occur.
And a boy’s paternal uncle might have the same Y. But it also might be so that the mutation has occurred in the uncle. It is all random. It is a very interesting question, for genealogy, to pick up these mutations.
I don’t believe that LE have one Y and don’t know whose Y it is. Because you virtually have to pick one cell with broken nucleus and harvest that Y. If there are two or three cells, you have got other chromosomes, too.
Mitochondrial DNA is probably something they have. It is tiny ring-cell structure, and you have the same as your mother’s one. A father and a son would have different mitoDNAs.
And much as mito DNA is tiny, mitochondrias are abundant, so it is easier to obtain it.
Now, there might be one case I am thinking about. A father and a daughter’s DNAs mix. Degraded sample, contaminated with other DNAs.
You will see a mix of two DNAs that are 50% alike, plus that Y from the father. If the sample is contaminated/degraded, they may not notice this 50% difference, this is when they’d end up with this Y...If they have the DNA of the mother to compare to, they will see the difference between daughter/father more clearly.
I don’t think Delphi is such a case, but we may see it in the future cases. Or maybe JBR could be that case if the police did a good job? Who knows. The