What is the relationship between Avram (Abram) and Sarai?

Answer From The Annual Reading Schedule - Week 3 Notes For Genesis: She was Avram's (Abram's) wife but also his sister, the daughter of his Father but not of his Mother (Genesis 20:12). This was done before it was prohibited to do so. At some point, such was probably the norm since the population on earth had to increase somehow. However, eventually this was outlawed later on in Leviticus 18:9.