Occurrence of Su in a German family.

Investigating a paternity case we observed a pretended opposite homozygosity of the S and s alleles between a mother and her child. The presence of the rare allele Su in this family could be demonstrated with the aid of dosage studies and blood group testing of the mother's parents. 22 additional genetic marker systems, including the HLA-system were examined, a biostatistical calculation was performed as well. The results obtained from these testings were in accordance with the hereditary rules and the posssibility of ilegitimacy or of children's substitution could be excluded. Only Caucasoid ancestry was known to the family. In addition, family members showed another rare blood group marker, the allele GPT0.