Its the genetics that makes them. Generally the harder they are to make, the more desireable they are. There are 3 types of gene:
- Dominant - Co-Dom - Recessive
Each morph requires a differant combination of genes which are supplied by the parents.
With dominant genes, only one of the parents has to have the gene to produce offspring with it. With co-dom genes, one parent can have the gene, and offspring could inherit it. If two snakes that carry a co-dom gene are bred together, the offspring will be visually differant to the parents. With ressesive genes, both parents have to carry it to make offspring that are visually differant.