The genes that code for the human leukocyte antigen(HLA) antigens, also known as the major histocompatibility complex(MHC) genes, are all located on human chromosome $6$. Two brothers and a sister participated in a bone marrow donor registration, and their HLA typing results are given.
| ID | HLA-A | HLA-B | HLA-C | HLA-DR |
|---|---|---|---|---|
| $1$ | A$1$, A$3$ | B$5$, B$7$ | C$3$, Cw$19$ | DR$3$, DR$9$ |
| $2$ | A$1$, A$6$ | B$2$, B$6$ | C$2$, C$16$ | DR$4$, DR$13$ |
| $3$ | A$1$, A$6$ | B$2$, B$6$ | C$2$, C$16$ | DR$4$, DR$13$ |