Swyer syndrome is a genetic disorder whose exact cause is not known, but it is usually due to alterations in the SRY gene. This gene is located on the short arm of the Y chromosome and is responsible for male sexual differentiation and masculinization of the external genitalia.
When a zygote is absent from the SRY gene or this gene is altered, the testicles are not formed and as a consequence, the phenotypic sex is female. However, the karyotype or set of chromosomes will be 46, XY. Therefore, there is no correlation between phenotype and genotype.