 Later, staining with DAPI, a more sensitive dye, revealed the DNA running through each loop and then returning to the axis of the chromosome.He also unveiled the structure and location of the rDNA, the part of the genome that specifies the ribosomal RNA and made many more important discoveries about nuclear structure.Gall and then-graduate student Mary-Lou Pardue wanted to find out where in the chromosomes a distinctive highly repeated DNA sequence called satellite DNA occurred.