Which consequence is least likely if HLA class I alleles were on chromosome 6 and class II alleles were on chromosome 7?

The statement indicating that class II would now assume more importance in matching for bone marrow transplantation is least likely to occur if HLA class I alleles were on chromosome 6 and class II alleles were on chromosome 7. Traditionally, the importance of matching for bone marrow transplantation is largely driven by the presence of class I alleles, which are crucial for the recognition of self versus non-self cells and play a significant role in graft-versus-host disease.

If class I and class II alleles were located on separate chromosomes, as suggested, the matching process would not inherently promote class II alleles over class I alleles. Instead, it could lead to a reevaluation of their roles in transplantation matching. Class I alleles would still hold primary importance because they are directly recognized by cytotoxic T lymphocytes, which are integral to the immune response in transplant scenarios.

The other consequences are likely to occur as a result of the separation of these alleles onto different chromosomes. Independent genetic inheritance of class I and class II alleles would necessitate family studies to assess them separately, and the linkage disequilibrium—which refers to the non-random association of alleles at different loci—would likely decrease. Moreover, crossover events between loci on different chromosomes are