Angus
I knew that I'd have to explain everything eventually; I just hadn't expected it to be so soon. I'd thought about how to do it for a couple of days, about how to start. Well, see, you're a vampire, same as me didn't quite cut it. And I hadn't expected to be factoring a normal fourteen year old teenager into the equation. I decided to use Marcus' terminology for now, and let the historical references drift through the conversation a bit later.
"Rebecca and I have something in common. We both use iron differently to other people. I have two brothers, Fergus and Marcus, who have the same, er, ability. Marcus has studied the basic physiological mechanics of how we use iron for a few years now, and he says that people like us are able to incorporate it into our tissues in different ways to normal people. The most important difference is a change in metabolic activity when we eat foods containing iron." Like blood, I thought.
"When we eat normal food, our bodies function like normal human bodies, using the usual metabolic pathways to extract energy from normal food types, mostly glucose, fats and proteins. But when we eat enough iron, our bodies switch over to a different metabolic pathway that has adapted to utilise molecular iron to increase the efficiency of many body functions." I looked at Rebecca. She was frowning, concentrating.
"Muscles work better, nerves conduct their messages faster, our bodies even heal faster, and are better at fighting off infections. And our skins are harder, because iron becomes incorporated into our cells, in the walls, so we don't exactly deflect bullets, but it's harder to hurt us." I paused, wondering how to continue.
"Our parents were also like us, and Marcus assumed that that would be the only mode of inheritance. But it looks like Rebecca here inherited it differently, recessively. That means that both your parents had to have the genes in their DNA, even though they weren't able to use iron themselves. Their DNA combined could generate an iron metaboliser. There's apparently a one in four chance. That's why you got the genes," I looked pointedly at Rebecca, "and your brothers didn't." I paused, expecting questions. I didn't have to wait long.
"So what happened today with Rebecca? It looked like she was going to die." Mark grimaced at the memory.
"She was dying. I'm not sure why exactly. I think something must have triggered her body to switch to the iron pathways, and she was using up all her red blood cells to feed those pathways. I had to give her a big dose of iron to stop that process, or it would have killed her." I wondered what could have precipitated the switch.