There are multiple types of inheritance mechanisms in humans. The well-known ones are include autosomal dominant, where only one copy of the gene is enought for the individual to express that characteristic. Another type is autosomal recessive, in which an individual must receive a copy of the gene from both parents in order for the gene to be expressed. The type concerning blood groups is codominance and it is when two different versions of a gene are expressed. Both of the alleles have a role in the appearance of the characteristic. Both the A blood group and B blood groups are dominant; however, if both alleles are present, the individual has an AB blood group.