Extent and high frequency of a short conversion between the human Aγ and Gγ fetal globin genes

Southern blotting and DNA sequencing after polymerase chain reaction (PCR) amplification provide evidence for the frequent occurrence (in 7 out of 24 chromosomes) of a short conversion Gγ→Aγ in the 3′ end of the human fetal Aγ globin gene. This short conversion is characterized by the presence, 3 nucleotides downstream from the termination codon of the Aγ gene, of the TCAC sequence that is normally present at the equivalent position at the 3′ end of the Gγ gene; it is therefore identical to a conversion already described. Interestingly, we have found that this conversion is associated with the presence of theHindIII polymorphic restriction site in the Aγ IVS2, occuppying an equivalent position in both the Gγ and Aγ genes. Our observations strengthen the hypothesis that the presence of the HindIII polymorphic restriction site in Aγ IVS2 and the presence of the sequence TCAC at the 3′ end of the Aγ gene might be the result of a single conversion event.