How can a DNA microsatellite be co-dominant if microsatellites are Short Tandem Repeats which in turn are typically non-coding?

Any DNA that does not code directly for the sequence of amino acids in a protein is non-coding or “junk” DNA. However it is important to realise that just becaue the DNA does not code for a protein doesn’t mean it does not do anything. Take humans and chimpanzees. The two species are very distinct. You are not going to mistake a human for a chimp but if you look at the DNA there is actually very little difference between the coding DNA for a human and the coding DNA for a chimp. The differences between the species comes not from the DNA that codes for proteins but from the “junk” inbetween. The coding section could be thought of as the building blocks while parts of the “junk” DNA could be thought of as the plans (not all the junk DNA of course some of it is actually junk and of no use what so ever).

Microsatellites are thought to have a role in gene expression. ie when and how a gene is used to make a protien.