The nonsense biology I can buy--it's the 24th century, and based on a remark made in TNG 02x20, it seems that someone has developed a gene splicing doohickey for interspecies couples, and it's existence is apparently well-known and often used, given the existence of B'Elanna, K'Ehleyr, Spock, and Troi--but the idea that it would result in some sort of split personality is dumb. Their personality should be informed by biology, but dominated by their cultural upbringing (like how Worf has a Klingon temper, but has a considerably more human-like personality than other Klingons and a strong understanding of human social cues.)