Ahem. that is in GT. GT is not Canon to the rest of the series. Akira Toriyama had no creative control over anything in GT. suffice to say: anything in GT can be completely ignored. though it probably won't, depending on whos doing the game-making...
and look at it from a genetic point of view.
Goku = 100% saiyan
Gohan = 50% saiyan
Pan = 25% saiyan.
Trunks = 50% saiyan
say Trunks marries and has a son with a human
Trunks's kid + Pan get married.
their kid: 25%. why? let's do a percentage. ok. they each have 25% add that together, you get 50%. nwo there's a whole 200% cuz we're counting both. 50 is, of 200, 25%. so the child would be 25%.
but, what if their 25% child married a person of 50% saiyan blood - say, Goten(eww, he'd be like, 60, though saiyans age slow)
25+50 = 75% of 200. that's roughly a combined total of 37.5% really, the highest they can reach is 50% saiyan, 50% human.
EDIT: also, it's highly improbable that anything GT will be involved, if Wikipedia can be trusted.
QuoteDragon Ball Online takes place on Earth, 216 years after the events at the conclusion of the Dragon Ball manga series
as you shold know, GT was never part of the DB manga.