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[C2] Introduction to the Genetics in Creatures 2 
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The Nymph (Administrator)
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Post [C2] Introduction to the Genetics in Creatures 2
Introduction to the Genetics in Creatures 2
Creatures is a simulation of life. It is so effective that the creatures themselves share many of the behaviors and responses of real animals, without any need to specifically program them. Just like a mischievous child, Norns don't always do what they're told and sometimes do the most unexpected things - providing a play experience that is never, ever the same twice!

You can even see how the creatures' genes change from generation to generation - as their pigmentation changes color or they become more friendly, perhaps even more intelligent. These sorts of changes occur when the genetic material inside your creatures is altered in some way.

This introduction to the genetics in Creatures 2 will, hopefully, make you want to take a closer look at the genes that control each aspect of a creature's biology - its pigmentation, biochemistry, gaits, instincts and brain structure. Who knows, you may start tinkering with the Creatures genetics so you can breed your own Norns with particular traits.


What are genes?
Real living systems are incredibly complex. Human beings have around 100,000 genes and each cell in our body carries a complete copy of them. These genes are strung out along structures called chromosomes, rather like beads on a necklace. Human beings have 46 chromosomes - 23 from the mother and 23 from the father.

Genes actually consist of a very long double-helix molecule called DNA or deoxyribonucleic acid. Without DNA (or in the case of viruses - RNA), life might never have evolved. DNA provides the instructions for manufacturing proteins; by chaining amino acids together, they become the proteins that make up our cells.

DNA in Creatures is called Creatures digital DNA™. It's not possible with current technology to model the process of genetics at the molecular level (though hopefully that day won't be too far away), however, CyberLife has stayed true to the principles of genetics; Creatures digital DNA contains a set of instructions describing structures; these structures create systems out of which behavior can emerge, just as in real biology.

In Creatures 2, Norns have 771 genes, while Grendels have 547 genes and Ettins 597 genes. Nearly half of the genes in each creature control poses and appearance; the rest are concerned with biochemistry, organs and brain structures. All of these genes are contained on a single chromosome so you'll find male and female genes on the same chromosome. When a creature is created, only the appropriately sexed genes are expressed - those from the other gender are carried but ignored.


Replicating chromosomes
The biological imperative in sexual reproduction is for offspring to get a mixture of genes from both parents. This is good news for us as it makes breeding Norns interesting. You can easily see a mixture of traits from each parent in your baby Norns - pigmentation is usually the most obvious.

The way in which genes are mixed during reproduction in Creatures is similar to the process you'd find in real living systems. The main difference is that most animals and plants have pairs of chromosomes (there are exceptions, like the garden worm) whereas in Creatures, each creature has just one chromosome.

During successful mating between creatures, the chromosomes are copied to produce a new one made up of genes from both parents. To prevent the loss of critical genes, each gene type is preceded by a standard header that indicates which errors are allowed:

Duplication - indicates that the gene can be accidentally duplicated
Mutation - indicates that individual information pieces within the gene can be mutated
Deleted - indicates that the gene can be deleted entirely.
As you'd expect, critical genes cannot be deleted entirely otherwise the Norn would not survive.

Replication of the chromosomes happens in a process called cross-over. Here's how it happens: The two chromosomes line up next to each other - one from the father and one from the mother. At first, the genes on one chromosome (in this case, the father) are copied, starting at the top (A). At point (B), cross-over happens and the code makes note of the gene identification number, its type and sub-type (eg 1-17) and moves over to the other chromosome (in this case, the mother) and identifies the same gene number before continuing to copy the chromosome. Cross-over may happen one or more times, (C) and (D), to ensure we have a mixture of genes from both parents.


My Norn's got 8 lungs!
It's important to understand how cross-over works as it explains some of the strange effects you can get. For example, you may notice that one of your Norns is missing an organ or has eight lungs. This happens when genes move around the chromosome and get out of sequence.

Suppose, when cross-over happened at point (B) that the corresponding gene (1-17) on the female chromosome had been moved and was now further down the chromosome. In this case, part of the female chromosome would not be copied and a number of genes will be missing. You notice this when a Norn is born with an organ missing.

Alternatively, if gene 1-17 had been moved further to the top of the female chromosome, then you'd get two sets of the same genes and a much longer chromosome will result.

Genes can get out of sequence quite easily. Suppose you decided you didn't want a particular instinct and deleted the gene (eg 3-8) for it. When you want to introduce another instinct, the Genetics Editor assigns a number automatically, reusing the deleted gene number 3-8, but places the new gene at the end of the chromosome rather than in its original location. Now the genes are out of sequence.

If you want to make sure two genes don't ever get separated, then always put them side by side. This will greatly reduce the chance of this happening.


Here are some things you can do
1. Study how pigmentation varies with time.
The pigmentation genes are spread along the length of the chromosome to increase the chance of cross-over mixing. Also, some genes are particularly prone to the mutation effects caused by radiation or heavy metals. With mutations, the genes are altered in some way and by making pigmentation very susceptible to mutation, we've encouraged the pigmentation in your Norn children to vary from their parents.

2. See how appearance changes over the generations
When you breed Norns you can see cross-over mixing and mutations happen to the appearance genes when you suddenly get a Norn with horns or one with a Grendel head as Brian Hershley discovered in his breeding experiments.

With the Genetics Editor (available from the Downloads Section), you can easily change the appearance of a particular body part by specifying the sprite type and donor species (Norn or Grendel). Suppose the donor species of a creature's head mutated from Norn to Grendel. You'd then get a very strange looking Norn! You'd have to breed quite a large number of Norns to get this to happen but you could tinker with the appearance settings to create some very unusual looking creatures - hopefully not too Frankenstein-like!

3. Change an instinct and see what happens.
You can have a lot of fun changing the Norn's instincts. Instincts influence what action will be taken in a given situation, as defined by up to three neural inputs. Let's take a look at the instinct - eat when hungry - and see how you can influence it.

Hunger is registered in the Drive lobe and when a Norn sees food, the food neuron in the Stimulus lobe fires. When both the hunger and food neurons fire, the message is passed onto the Concept lobe so the Norn registers that it is hungry and there's food around. This causes an 'Eat' neuron in the Decision lobe to fire and gives the Norn the signal to eat whatever food he can see. (For more details about the structure of the Norn brain, read the article which appears on the Creature Labs site.)

The Norn learns that eating is a good idea. Having eaten, the Stimulus gene monitors that it has eaten something and this causes hunger to decrease and for two other chemicals to be released. If you want to play around with an instinct, you could remove the gene that says 'I'm hungry, eat' and see what happens. You'll find that it will learn to eat when hungry but how long will it take?

Here are some of the stimuli you could play around with:

See what happens when hunger doesn't decrease after the Norn has eaten - you'd expect him to carry on eating and get fat. However, he may not continue eating as he won't be rewarded for it.
Increase the boredom drive and see if the Norn goes off to find a toy to play with.
Increase both the boredom and loneliness drives and see if the Norn becomes more friendly as he searches out another Norn.
Further reading
If you'd like to learn more about genetics and how it works then we can recommend The Cartoon Guide to Genetics. This book is an excellent introduction to genetics covering reproduction, inherited traits, chromosome replication, biochemistry etc. The book doesn't assume any knowledge of science or maths and is genuinely fun and readable.


Sat Jun 21, 2008 11:02 pm
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