A cord blood typed to have more than 2 HLA-A and more than 2 HLA-DRB1 alleles is least likely explained by which of the following?

The presence of more than 2 HLA-A and more than 2 HLA-DRB1 alleles in a cord blood sample is primarily associated with the genetic variation of the individual. When considering which explanation is least likely, the detection of new alleles does not logically account for the observed fact.

Typically, an individual inherits just two alleles for each HLA gene—one from each parent. The situation of having more than two alleles for HLA-A and HLA-DRB1 in a typical diploid organism would indicate the presence of either maternal blood or contamination, as these scenarios would introduce additional alleles from another source.

Therefore, the explanation involving the detection of new alleles, while interesting in a broader context of HLA typing, does not logically fit within the parameters of classical inheritance. New alleles would generally not account for the findings in a single individual's sample unless there were unique but improbable genetic phenomena at play, differentiating them from the more straightforward reasons of contamination or maternal blood interference.