If infant has PKU, child is placed on diet low in phenylalanine until brain is fully developed. Pedigree charts show pattern of inheritance within a family. A carrier is a heterozygous individual who has no apparent abnormality but can pass on an allele for a recessively inherited genetic disorder. Autosomal dominant and autosomal recessive alleles have different patterns of inheritance. Heterozygotes are affected.
Most affected children have normal parents since heterozygotes have a normal phenotype.
Two affected parents always produce an affected child. Polygenic inheritance occurs when one trait is governed by two or more sets of alleles. A hybrid cross for skin color provides a range of intermediates. Includes cleft lip, clubfoot, hypertension, diabetes, schizophrenia, allergies and cancers. The ABO system of human blood type is a multiple allele system.