He was an expert in childhood adversity, monoamine oxidase a genotype, and risk for conduct disorder.
It has long been known by now that successful generations of clones are subtly different, a bad copy, of their original genotype.
Identical twins will have the same DNA, genetic material (genotype), but it may be expressed differently (phenotype).
Subsequent diagnostic procedures (called mutation analysis and genotype determination) can actually identify the specific types of PAH gene mutations inherited by PKU infants.
The 'Mary' sisters, for instance, might have elder Mary, the genotype, followed by Maggie, Molly, Mirian, and so on, all spaced a year or two apart.