Look
into the mirror. What kind of colour of your eyes do you have?
Brown, blue, grey or maybe even green? And if it's blue, why
isn't it brown? Mostly you will get the answer: "You got
that from your parents.". But they still have their colour,
so how can you've gotten it from them? Let's make it short:
Yes, it's true, you got "it" from your parents, but
the whole thing isn't that simple.
Look at you again in the mirror. Now you will see that you do't only have eyes, but also ears, hands, arms, legs, feet, hairs (and those have a colour as well!) and that's only what you can see in a mirror.
Have
you been X-rayed once? Maybe you've seen on these pictures that you
have an also interesting "inside"! You've got bones, a stomach,
lung, a heart and lot's of blood vessels and they all thoghether do
something in your body. Somehow genius, don't you think? It all works
without you giving a thought about it.
How works it anyway? Well, you're kind of "programmed". Never thought you get compared to a computer program, huh? :-) But in fact, you have a kind of memory inside of you where everything is written on, how you have to look like. E.g. the colour of your eyes, how tall you are etc. This memory is called the "genome".
Understood that? Okay, then let's go on. We will soon come to norns but just let me explain some terms.
The memory in your
computer is called a hard disk or a CD ROM etc, and in your
body it's called the genome.
The genome is divided into a lot of smaller parts of memory.
There's a part which e.g. contains the information for the colour
of your eyes. These "smaller parts" are called "genes".
So there you got an eye-colour gene (in fact, there must be
several genes which contain each a part of the whole information
for the colour of your eyes, the colour is defined by several
genes. But let's not be too pedantically. ;-) Accept, that you're
a VERY complicated creature and I can't tell you all the details,
otherwise this side here is not enough...!)
The memory of your computer consists of plastic and metal.
Your personnally one consists of DNA. That's short for Desoxyribonucleic
Acid. Acid? No, don't worry, you're not acidic at all because of that,
it's just a complicated name for a complicated build organic substance.
Yep! Organic! Your build very environmental friendly, don't you think
so?
And how come you get to such a genome? Well, that's where your parents join in again. Half of the amount of your genes you inherited from your mother, the other half is from your father. You inherited a bit of DNA from each of your parents (no problem, there's lots of it around in a body and get's rebuild all the time in anyway). Set together that's now your DNA. If you're going to have a child, that child will inherit also a bit of your DNA. Have you got a sister or a brother? How come he/she doesn't look exactly like you, even if both of you have the same parents? There are sooooo many genes present in a human, the chance you and your sister or brother get exactly the same genes from both your father and your mother is almost impossible (except identical twins)! So you're unique!
Now let's talk about Norns! 
I told you all these complicated things, cause the people, who developed Creatures took the humans as a model for their simulation of life and the norns. The nornic DNA is not an organic substance but just exists in your computer, therefore they called it "digital DNA". There's lots of mathematics and a programming language behind all that. With that digital DNA the genes where build and all the genes together build the genome of a norn, a digital genome.
So when two norns get a child by means of "kisspop", the child's genome is build of half of the mother, half of the fathers genome. That's why there will always be new and exciting recombinations! (btw: Unlike norns, humans do NOT get pregnant by kissing each other! :-))
But sometimes a norn looks VERY different than it's parents do or it's body shows some damages. The genome resp. the single genes can "mutate". A mutation is a sudden changing of the "information" on the DNA. It's qutie the same for humans. These mutations ocur naturally also in humans but can be multiplied and/or intensified by some substances, such as radioactivity or chemicals. The norn genome can mutate naturally but mutations can be triggered when norns live to near the vulcano and get poisened by heavy metals. It's offspring can inherit a part of it's damaged DNA and if it's damaged too much, the norn baby might even die. Btw, mutations in human genes can have the same fatal effect ...
The genome and it's genes can be altered deliberately by means of an editor (doesn't work yet with human DNA!;-)). There's the Genetic Kit from Creature Labs you can now download at the Creatures Developer Network for free (find there also some Tutorials ), the Genom Editor from Chris Double and LiveGMS of course. You can e.g. program new norn's colours or change it the way it never get's sick any more. Here's an example what the organ "lung" looks like (in the Genetics Kit)
Complicated? Well,
true! But I already told you that a norn 's quite a complicated
creature! ;-)
The original norn genome contains
811 genes. You can add some more without problems, for example
pigment genes for fur colour of the norn, or you can delete
genes as well.
Maybe you already noticed the long file names the norn files
have? This is a guarantee that each norn has it's distinct file
name and can be distinguished from other norn files. Quite long...but
that's also called "moniker" and you can find the
.gen file for every living norn in your game in the folder my
worlds\nameoftheworld\genetics and you can load those files
into a genetics editor and alter it.