In Mass Effect, Turians and Quarians seem very similar in physical shape and physiological characteristics. They have the same number of digits on their hands and similar foot and leg structure. They also both have dextro-amino based bio-chemistry; iccidently the only two sentient species known to have that biochemistry. Has there been any word or hints from Bioware as to whether there is some connection or is it just a weird coincidence?
Based on that logic, one could argue that Humans and Asari are related. After all, they seem very similar in physical shape (hair excepted) and physiological characteristics. They have the same number of digits on their hands, and identical foot and leg structure. They also both have Levo-amino based bio-chemistry.
The point I'm trying to make is that they may appear similar, but are wholly separate races. They have different homeworlds (Palavan vs. Rannoch), different social structures (Turian Clans vs. Quarian Ship-based loyalties), wholly different immunologies (Turian carapace developed because of the radiation of Palavan's sun; Rannoch had little microbial life, so Quarians had weak immune systems before their exile, which has really weakened it), etc.
I suppose it's possible that they're both genetic experiments by the reapers, but everything Bioware has done has classed them as completely and wholly separate.