<prompt> Human leukocyte antigen HLA which plays an impoant role in graft rejection is present on chromosome:Sho arm of chromosome 6Long arm of chromosome 6Sho arm of chromosome 3Long arm of chromosome 3  <response>: The genes for the HLA antigens are clustered in the major histocompatibility complex MHC, located on the sho arm of chromosome 6. Three of these genes HLA-A, HLA-B, and HLA-C code for the class I MHC proteins. Several HLA-D loci determine the class II MHC proteins i.e., DP, DQ, and DR. Ref: Levinson W. 2012. Chapter 62. Major Histocompatibility Complex Transplantation. In W. Levinson Ed, Review of Medical Microbiology Immunology, 12e. 