But it isn't just that it's "small in quantity" that means that there is a problem. Amanda was a housemate, it would be incredible if her DNA couldn't be found

But it isn't just that it's "small in quantity" that means that there is a problem. Amanda was a housemate, it would be incredible if her DNA couldn't be found in her housemate's room. The simplest explanation for Amanda's DNA being in the room is that she had previously spent some time there talking to Meredith. To put this another way, have a think about where you would expect your own DNA to show up. At home, at your partner's appartment, at the office, at the cafe around the corner from the office, in your car, in your partner's car, at your best friend's home, your best friend's car. If a murder ever took place in one of these locations, how would you feel about the presence of your DNA being used to implicate you in the murder?