Brother and sister dating each other
In the case where the unshared parents are identical twins, the children share as much genetic material as full siblings do.In this case, a woman has children with two men who are father and son, or a man has children with two women who are mother and daughter. Furthermore, the two offspring will have an aunt/uncle-nephew/niece relation.Furthermore, environment influences personality substantially; however, it has little to do with whether they are reared together or apart.This study also suggests that heritability is substantial, but not as substantial as for younger subjects; it has less significance later on in life.
This is very rare and is due to there being a smaller possibility of inheriting the same chromosomes from the shared parent.
Adoptive siblings are legally related but need not be blood-related or biologically related.
Research was done to see what factors affected IQ, specifically family environment and genetics.
They gathered subjects with a mean age of 59, who included 99 pairs of identical twins, and 229 pairs of fraternal twins who were all reared apart.
They also gathered twins who were reared together: 160 pairs of identical twins, and 212 pairs of fraternal twins.