Half-siblings

There are two kinds of half-siblings, with varying degrees of consanguinuity (blood-sharing):
 * uterine sibling refers to when you share the same mother (the same uterus) also called a maternal half-sibling
 * agnate sibling refers to when you share the same father (from agnatus, paternal kinsman) also called a paternal half-sibling

A sub-group of half-siblings are three-quarter siblings (3/4 or 0.75). This occurs when the unshared parent has mean consanguanuity of 50%. This includes full siblings and parent/child. There are two kinds of 3/4 siblings:
 * horizantal: when the unshared parents are siblings, such as a man impregnating two sisters, or two brothers impregnating the same woman
 * this makes the 3/4 siblings first cousins, too
 * in the case of the unshared parents being identical twins, they are effectively full siblings
 * vertical: in the case of the unshared parents sharing a parental relationship, such as a father and son impregnating the same woman, or a man impregnating a mother and daughter