The present invention relates to a method for determining the genotypes of
polymorphic loci amplified in a mixture of restriction fragments, using
an oligonucleotide sequence that is essentially complementary to part of
the target restriction fragment, and located adjacent (upstream) to the
polymorphism to be detected. The method involves contacting the mixture
of restriction fragments with the oligonucleotide sequence under
hybridization conditions, such that when the target restriction fragment
is present, a hybrid is formed between the target restriction fragment
and the oligonucleotide sequence. When the resulting hybrid has at least
one unpaired nucleotide of the target restriction fragment and the
oligonucleotide being present, and the at least one labeled nucleotide or
nucleotide analog is complementary to the at least one unpaired
nucleotide of the target restriction fragment directly adjacent to the 3'
end of the oligonucleotide sequence, the nucleotide sequence is extended
with a labeled nucleotide or nucleotide analog, which can be detected.