Abstract
Albinism appeared in the globe-eyed goldfish (demekin) is not a simple Mendelian character but is the double recessive of two independently assorting autosomal genes since non-albino and albino types appear in the 15:1 ratio in the F2 generation. When scored on advanced embryos and larvae, however, the dark (normal), the light and the albino types appear in the 12:3:1 ratio, related in action of dominant epistasis.
Symbol M is proposed for the epistatic dominant gene responsible for normal melanin deposition as well as normal melanophore development, S for the hypostatic dominant gene governing slower melanin formation and slower melanophore development. The effect of the S is masked in the combination M, S, because of epistasis of the M to the S (M>S). The dark type, thus, is represented by either M, S or M, s, the light one by m, S and the albino by m, s. The F2 ratio scored on embryos and larvae becomes 12 dark (M, S and M, s): 3 light (m, S):1 albino (m, s).
In the light embryos and larvae, eyes darken slowly and melanophores are smaller in size and fewer in number, i.e., in earlier developmental stage. The degree of phenotypic divergence between the dark and the light types is gradually obliterated as development proceeds. Final melanin deposition as well as final state of melanophores become eventually the same since the two genes differ only in the time-relationships in the developmental process.
The M and the S act in the same sense like duplicate genes. Since, however, M>S in epistasis but not M=S, the mode of non-allelic gene interaction in this case may be termed as a dominant epistasis akin to duplicate genes.
The presence of the M and the S genes pertinent to melanin as well as melanophores in a number of the ordinary black-eyed varieties of the goldfish is pointed out.
