Yes, it too will have some effect on the sex of the person, as any deviation from the normal genotype causes some or the other disorder Klinefelter's syndrome is a genetic disorder caused when someone has two X-chromosomes and one Y-chromosome (XXX) It affects male physical and cognitive development. Affected individuals have small testes gynecomastia and are usually infertile. Now, if you change it to XYY condition, the disorder will also change. You will be glad to know that the disorder with XYY already exists and is known as Jacob's syndrome. A person with this syndrome would most likely to be tall and more aggressive due to over production of male hormones,