A good idea is to keep two separate, but related, lines of the same strain and cross these lines each fourth or fifth generation. This postpones the urgency to bring in unrelated lineage for more generations. Characteristics of an angelfish are determined by its array of genes. Dominant genes express themselves when crossed with other genes it can predominate or act in codominance with. For example, the genotypes for the true breeding black angelfish are considered a dominant gene when crossed with a gold angelfish.
Recessive genes express themselves only when crossed with another related recessive gene.
The genotypes for the pearlscale angelfish is considered a recessive gene just as the gold angelfish genotype whereas the characteristic desired will only express itself if both parents carry the allele. A simple way to determine phenotypes is to designates single letters for individual characteristics. Both the female and male genotypes are combined to form the offspring's characteristics. Simple multiplication can be used to give theoretical ratios. A diagram can be used to visualize what characteristics a breeding pair would produce in what is called the Punnit Square.