Homozygous recessives from inbreeding

Pedigree of a rare recessive phenotype determined by a recessive allele a. Gene symbols are normally not included in pedigree charts, but genotypes are inserted here for reference. Personsand II-5 marry into the family; they are assumed to be normal because the heritable condition under scrutiny is rare. Note also that it is not possible to be certain of the genotype in some persons with normal phenotype; such persons are indicated by A/–. Persons III-5 and III-6, who generate the recessives in generation IV, are first cousins. They both obtain their recessive allele from a grandparent, either I-1 or I-2.