Not that much for genetics, though the rest is pretty stellar.
- Medic: "He's lost a lot of blood"
- Robot: "Sarah Connor is O-. Universal donor."
- Medic: "He needs at least three pints of his own blood type: AB-"
- John: "Test mine."
If your mother is O, the chance you're AB is 0%. My mother is AB the chance that I could be O is 0%. You get one gene or the other, if you have no gene to give you have O. Regardless what version of the gene John got from his father, his mother doesn't have the other gene to give him. With a mother who has AB, I can have A, B, or AB. Depending on my father's blood type (B heterozygous). I have B.
John, ofcourse, had the right blood type. This forces me to conclude that John's mother is not Sarah Connor. -- Odd. I understand the switching to a new timeline, but why exactly are they changing facts established prior to John's conception?
A commenter informed me of a good explanation of this.
Linda Hamilton's Sarah Connor must have had a blood type to allow John to have AB- whereas Lena Headey's Sarah Connor has type O- blood. The mother currently in this show is clearly different than the mother who gave birth to him; everything makes perfect sense now.