Zero allele

A null allele is an allele whose effect is either the absence of a gene product at the molecular level or the absence of function at the phenotype level .

An example are the human blood groups A, B and 0. The alleles for the A and B antigen are codominant , so they are both expressed if both exist. The 0 allele, on the other hand, is identical to the A antigen allele, but with a base substitution that is probably due to mutation . The protein so encoded is dysfunctional, which has a phenotypic effect in the absence of any antigen. Thus the group 0 allele is a kind of zero allele.

With respect to genetic markers , null alleles are the loss of a marker, e.g. B. microsatellites , by mutation during the PCR process. By changing the sequence to which the primer binds, the corresponding section cannot be amplified and the allele becomes a null allele. This can lead to misinterpretations e.g. B. lead in paternity analyzes.