How can marker analysis determine which hla alleles are present?

Marker analysis is going to screen and look for alleles present in the code.  HLA are controlled by the Major Histocompatibility Complex, which is a set of genes all located together in the same bunch.  Marker analysis just detects molecular similarities in gene code, so it's best suited for this job.

If the experiment was perfomed more then once and you get the same results