“[G]eneticists have... been able to zero in on a... gene, {{w|FOXP2}}... implicated in one particular disorder affecting speech and language... [[w:Mutation|[M]utation]]s have been heterozygous... [i.e.,] a mutation in only one copy... (Humans are diploid organisms carrying two copies of every gene, one from the father, the other from the mother, with... exceptions such as the genes on {{w|sex chromosome}}s.) ...[C]ases of FOXP2-related disorder suggest ...reduced ...FOXP2 {{w|protein}} in the brain circuits... important for speech and language.”