Heteroduplex question

People with the recessive disease, Purple Tongue Syndrome, are unable to make the enzyme Blue Pigment Decolorase (BPD). You isolate mRNA from a person (P) afflicted with the disease and from a normal person (N) and do the following:
i. Mix excess P mRNA with cloned genomic DNA carrying the BPD gene and, separately, mix Normal (N) mRNA with the same DNA.
ii. Raise the temperature of the mixtures, and then cool to allow RNA-DNA hybridization to occur.
iii. For each mixture, locate by electron
microscopy heteroduplex molecules.
"Heteroduplex" here refers to hybrid
molecules in which one strand is mRNA and
the other BPD DNA. The cartoon to the right
is supposed to be what you see by electron
microscopy.
Double-stranded regions are represented by
thick lines, and single-stranded regions are represented by thin lines.
 
a-The single-stranded loops are composed of which: RNA or DNA?
Why?
b- What is the single-stranded region at one end of the heteroduplex?Why is it single-stranded?
c- What is the molecular cause of Purple Tongue Syndrome based on the hybridization experiments?