"Ana Charrua" <ana_charrua at yahoo.com> wrote in message
news:94062i$91u$1 at venus.telepac.pt...
> Is it possible that a mutation could change the phenotype of "O" to "A" or
This is theoretically possible but, in reality, the answer is no.
The other way is much more likely, going from A or B to O.
The details are given in
Essentially, the ABO gene codes for an enzyme that catalyzes
the last in the series of reactions producing the glycoproteins
that are the blood type antigens. The "O" gene produces a
non-functional enzyme. Most of the mutations that produce this
allele start as single nucleotide deletions from the functional gene.
It is theoretically possible to have a mutation producing a single
nucleotide insertion of exactly the right type at exactly the right
location, but it is so unlikely as to be virtually impossible. In fact,
most people with type O allele have other mutations in this gene
besides the deletion, so converting back to a functional type
A or B is then really impossible.
The A and the B alleles differ at six nucleotides, so one mutation
cannot convert one to the other. However many single mutations
can convert an active A or B enzyme to a non-functional enzyme
producing the O allele.