Background and objectives: Amerindians are blood group O, but the dist
ribution of the various O alleles is unknown. Their ABO genotypes were
compared with samples from other Brazilian ethnic groups, Materials a
nd methods: Genomic DNA was examined by PCR-RFLP analysis, PCR-SSP and
direct sequencing. Results: An unusual allele distribution was found,
with 91% of the O alleles being O-lvariant. Almost half of these alle
les had an additional novel mutation (G542A), which was also detected
in a few other Brazilian and European samples. The O alleles correlate
d completeley with ABO-related haplotypes previously determined by Sou
thern blot. Conclusion: The three Amerindian tribes represent a homoge
neous (ABO blood group) population, except for the G542A mutation. The
presence of this mutation in all other populations examined suggests
that it originated before the migration of man into America.