Angelfish Genetics

This section will give you a basic overview of genetics and how it applies to angelfish. Much of the information on angelfish genetics contained  here, has come from Dr. Joanne Norton's research on angelfish genetics and from the practical knowledge obtained by Steve Rybicki, with the hundreds of crosses he has made over the last 25+ years. Dr. Norton's information on angelfish genetics was first published in FAMA Magazines articles starting in the early 80's. A majority were published by the end of 1992. Dr. Norton's angelfish genetics research was later published in a couple books, one put out by Tetra in 1992 called Aquariology. Steve personally confirmed all these crosses in his hatchery before 1990 with the exception of Albino and Streaked, which came out later.

The angelfish gene names used here are those that were originally used by Dr. Norton or the person first researching the new angelfish gene mutation (up until now, no one else has done any documented research that has demonstrated the inheritance characteristics of any gene mutations in angelfish). Many different common angelfish names are used, so it is important to also attach universally used angelfish gene names for the alleles that are proven in any particular angelfish strain.

Genetic Terms

Gene: Genes contain the genetic material by which hereditary characteristics are transmitted. Each gene occurs at a specific location (called locus) on each chromosome, whose existence can be confirmed by allelic variants (mutations). Chromosomes occur in pairs, one coming from each parent. Therefore, each gene has an opposing gene on the other chromosome.

Allele: Alleles are the mutational variations of a gene that can occur at each locus. Each is distinguished from other alleles by the effect it has on phenotype. There may be several alleles possible at any given location, though no more than two can occur at the same time in any individual.

Dose: A term commonly used to designate the allele donated by a parent. For example, a Double-Dose Black means that each angelfish parent transmitted one allele of Dark to the offspring.

Hybrid: An angelfish trait that was derived from two different alleles. The angelfish hybrid will not breed true, however, a percentage of the hybrid's offspring will be true breeding.

Mutation: The process of mutation is the source of new alleles. It is an abrupt and permanent change in the genetic material. Minor mutations are relatively common and somewhat insignificant. They are either slight or have no desirable quality. Since mutations are random in the genetic code and the proper code is very specific, useful mutations of a major proportion are rather unlikely. Truly valuable or significant mutations are quite rare. In angelfish, there have been no more than 2 to 3 dozen major mutations that were perpetuated in the last 50 years. The gradual change in the looks of a fish, over many generations, is also caused by mutations. The result  is simply the accumulation of less significant, minor mutations.

Homozygous: A trait determined by two identical alleles at the same locus, resulting in a true breeding strain for that trait. i.e. a true breeding Double Dose Black is homozygous for Dark.

Heterozygous: A trait determined by two different alleles at the same locus, resulting in a hybrid angelfish that will not breed true for that trait. i.e. a single dose of Dark and a single dose of it's allele, Gold, will produce 25% homozygous Blacks, 25% Gold and 50% single dose Blacks that have a single dose of Gold, thus the single dose Black is heterozygous for Dark and Gold.

Recessive: When different alleles occur at the same locus and one of the alleles is not expressed in the presence of the other, the non-expressed trait is considered recessive.

Dominant: When different alleles occur at the same locus and one of the alleles is not expressed in the presence of the other, the expressed trait is considered dominant.

Intermediate Inheritance: When different alleles occur at the same locus and there is a blending of traits, each trait is an incomplete-dominant (or Co-dominant). In Black Lace Angelfish is there is a blending of traits, therefore Dark and Silver (wild type) act as incomplete dominants to each other.

Phenotype: The physical appearance of a trait. To be considered a distinct phenotype the trait should be uniquely identifiable.

Genotype: The written expression of the genetic makeup of the trait in question. With angelfish we use one or two letter notation to represent this. There are two notations for each gene location. For example,  Gm/g represents two possible alleles that could be found at this location - Gold Marble (Gm) and Gold (g)..

Penetrance: Expressed as a percentage. It is the frequency with which a given genotype expresses it's mutant phenotype to at least some degree. A good example is Halfblack angelfish, which is influenced by environment. 100% penetrance occurs under ideal tank conditions with some lines. If at least a partial pattern develops on all the angelfish, then 100% penetrance has occurred. Some Halfblack angelfish lines appear to contain modifiers that inhibit the expression of Halfblack. In these lines, penetrance will be less than 100%, even under ideal conditions.

Expressivity: The degree or range in which a phenotype for a given trait is expressed. Once again, Halfblack is a good example. This mutation can exhibit a wide range of expressivity. Halfblack angelfish patterns are seldom complete on every fish in a spawn. Various degrees of partial patterns are somewhat normal. This range can be due to incomplete penetrance and well as adverse environmental conditions.

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