Researchers have identified specific gene variants in the receptors that detect sweetness: TAS1R2 and TAS1R3. There is also high variation in the detection of bitterness. However, the story is more complicated than sweet taste, as we have 25 receptors that detect different bitter molecules
The answer is Liver disease
Sex linked inheritance usually occurs on the X chromosome. Males have one X, meaning if they receive the specific sex linked gene, they will have the trait. However for a female to possess the trait, she must receive 2 X chromosomes for that trait.
I would say D. natrural selection