title: Extensions of the classical twin method.
mesh_terms: D005260:Female; D014644:Genetic Variation; D005824:Genetics, Behavioral; D006801:Humans; D008297:Male; D008957:Models, Genetic; D011247:Pregnancy; D012641:Selection, Genetic; D014427:Twins; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic