Practice question

For autosomal recessive inheritance, heterozygous individuals are healthy carriers because one normal allele suffices for normal physiological function. When two carriers mate, Mendelian segregation predicts twenty-five percent homozygous recessive affected, fifty percent carriers, twenty-five percent normal homozygotes among children on average. Thus affected children typically arise from phenotypically unaffected parents who each silently harbor mutant allele. If one parent were homozygous affected, every child would be at least carrier and half affected, but classic recessive pedigree hallmark shows unaffected carrier parents producing affected offspring.