A blood stain from a crime scene and blood samples from four suspects were analyzed by PCR using fluorescent primers associated with three STR loci: D3S1358, vWA, and FGA. The resulting electrophoretograms are shown below. The numbers beneath each peak identify the allele (upper box) and the height of the peak in relative fluorescence units (lower box).
(a) Since everyone has two copies of each chromosome and therefore two alleles of each gene, what accounts for the appearance of only one allele at some loci?
(b) Which suspect is a possible source of the blood?
(c) Could the suspect be identified using just one of the three STR loci?
(d) What can you conclude about the amount of DNA obtained from Suspect 1 compared to Suspect 4?