Investigation of candidate loci and variations within the homopolymeric stretches. (a) A triple alignment of pT684 to two outgroup species, the rhesus macaque and the common marmoset. The TSDs are highlighted in grey, the poly(T) stretch in green, and the L1 is highlighted in blue. (b) A gel chromatograph of polymerase chain reaction products depicting an insertion present in humans, chimpanzees, gorillas and orangutans, but absent in rhesus macaque and owl monkey. (c) Internal primers were designed around the poly(T) stretches for all human-specific loci; two loci are shown here. For each locus, HeLa DNA and a mixture of the DNA of 80 human individuals was run out on a 4% agarose gel with 100 bp and 20 bp ladders. No within-species variation in poly(T) length was observed.