With some exceptions, inheritance of HLA genes follow classic Mendelian genetics. However, in about 2% of mating, there is a chance of recombination where genes on tetrads are switched during meiosis.
Siblings have a 25% chance of being identical at the genotypic level of HLA molecules. Immediate family members make great starting points for bone marrow and organ donations because of their higher probability of matching. Many a times non-familial, altruistic allogenic donors are used through various national and global registries.
HLA molecules are codominantly expressed, which is similar to the ABO/Rh system in erythrocytes.
Individuals express both haplotypes of HLA genes inherited from each parent. Just like in blood bank, there are two types of expression: homozygous or heterozygous. If a person received two of the same genes then they are homozygous, and if a person received two different HLA genes, the person will be considered heterozygous.