Full siblings have both mother and father in common. They each inherit half of each of their parent’s chromosomes and thus full siblings will share 50% of their genetic make-up. Monozygotic twins or identical twins are the exception as they will share 100% of their DNA.
Half siblings will share only one common parent (either the mother or the father). If the siblings have their biological father in common (therefore, have different mothers) is known as an agnate siblings. If the siblings share the same mother but have different fathers, then they are commonly called uterine siblings. The common DNA in half siblings is far less than that of full siblings and is in fact, normally expected to be 25%. Sibling Relationships can easily be tested using Relationship DNA tests. Relationship DNA tests can tell you whether you have common parents by doing what are known as sibling DNA tests (types of relationship DNA tests); thus, whether you are full siblings, half siblings or not siblings at all.