Phantasians are defined by genes – hundreds of them! Each gene creates some kind of biological structure, perhaps a muscle, a chemical, a cluster of neurons in their brain, or a piece of the brain’s wiring. Without these genes, the creatures wouldn’t exist.

The genes are responsible for each creature’s characteristics and personalities, but not in any trivial way. In most ‘pet games’ and artificial life simulations, the genes are simply numbers that define the amount of something, much as a character in a D&D style of game might be assigned a certain strength, a certain proficiency with magic, and a certain level of aggressiveness. In other words, these systems define the creature’s phenotype very explicitly.

In natural living things, it’s vastly more complicated. A single gene produces a single protein, but that protein will almost certainly interact with many others. During the growth of an organism, these interactions can be extremely complex. Your liver is not defined by one gene, nor even hundreds of “liver genes”. A gene that influences the development of the liver in some way, may also influence the development of many other parts of the body.

In Phantasia, the genetics lie somewhere between these two extremes. Each gene produces and configures a single, sometimes quite complex structure. The creatures’ brains, for instance, are made from many different clusters of neurons, which we can think of as “modules”. Each module is mostly defined by a single gene that configures the many characteristics of that particular module. There’s no such thing as a “module for walking”, though – walking happens because of the interaction of many brain modules in many places, some of which would have a very different significance if they grew somewhere else.

Phantasian genes are stored on several chromosomes, which come in pairs. In natural life, every single cell contains an identical set of these pairs, apart from the sex cells (eggs and sperm), which effectively contain only one half of each pair. Phantasians are quite similar, except for the fact that they are not made from billions of individual cells, and so don’t have billions of copies.

Nevertheless, they do have multiple pairs of chromosomes. Each chromosome is made up of a long string of genes, with each chromosome in the pair generally having the same layout of genes. For example, the thirtieth gene on chromosome 3 might be a gene that produces a particular enzyme, involved in digestion. There will be two alleles for this gene, one on each strand of the pair. Although both of them would probably produce the same enzyme, they may each specify a slightly different variant of it. Perhaps the allele on strand A specifies a variant that breaks down fats more quickly than the variant defined by the allele on strand B.

Which allele gets to make the actual enzyme, depends on which is dominant. If the allele on strand B happens to be more dominant than the one on strand A, the allele on strand A is suppressed, and the creature will only produce the variant of the enzyme defined by strand B, which in this case breaks down fats more slowly.

This competition between pairs of alleles is quite complex, and ensures that every creature will be quite unique, showing characteristics that depend on which alleles it inherited from its two parents, and which ones turn out to be dominant.

Note for Creatures fans: In Creatures, the Norns were monoploid, meaning that their genes were not paired, and there was no such thing as dominance (there was crossover, though, so that children did inherit traits from both parents). Diploid creatures, with two copies of each gene, inherit traits quite differently. For instance, two brown-haired creatures might conceive a blond-haired child, because of the genetics of its grandparents. Things now work in the confusing way you were taught in school!