Kohaku Koi is always occupying my mind with a huge interest. However, there's not much information about them so far, like their origin, possible phenotypes / polymorphism, and underlying genetics mechanism that created such a cool creature (in my opinion). So, while keep searching for their archive, waiting for more research data introduced by other breeders, I would like to do something ... such as proposing a hypothesis from my observation on Kohaku strain. Although Kohaku Koi swordtail is collectively suggested as a Red and White swordtail model based on their color development (see Red and White swordtail classification by Mr. Rainer Rekord), I still feel very eager to explore more of the mechanism that controls Kohaku coloration because in my opinion it is pretty far different from the one of Piebald swordtail. Here is something I would like to share to fellow breeders: - Kohaku Koi is known as a recessive color gene. However, by observing popular phenotype [Red-White-Red] from my line development as well as from many other breeders' line, I would suggest that Kohaku phenotype is pretty much caused by the loss of function in Red pigment production gene. The suppression of this gene is likely stopping red pigment to be expressed in skin, thus exposing a large white pattern on the host body. - As proposed by some research documents, the red coloration is controlled by some genes of a family: 1) Red cap [Hr] gene: express from top head, extend to mouth, gill, neck, chest, then pectoral fins. 2) Dorsal red [Dr] gene: express from high back, around body down to belly, up to dorsal fin if being strong enough. 3) Red tail [Tr] gene: express from caudal peduncle covering lower body till anal fin, also may extend to caudal fin if being strong enough. Following that suggestion, popular Kohaku Koi phenotype [Red-White-Red] is assumed to be the loss of function in Dr gene [Dr-]. As the matter of fact, when being under strong expression, Hr or Tr gene may cover part of Dr expression region, even overlapping each other, but a suppressed Dr [Dr-] always show a triangle of white pattern as shown in the second picture below. Red cap phenotype (picture #3): In a rare case, we see a phenotype called Red cap, which is only Hr express on the host body, both Dr and Tr are suppressed. And if never before you found a true Kohaku Koi with milky white head without any red spot, would you think Hr gene is lethal when under suppression? Orange blossom phenotype (picture #1): I saw some people called a non-standard Kohaku Koi (with white spot at stomach) as Orange blossom. But from my experience, this phenotype showed 100% when you cross a pure Kohaku Koi to a Red swordtail in purpose of increase redness of the Kohaku strain. That meant the F1 phenotype is heterozygous Kohaku Koi [Dr Dr-]. When this phenotype happened in F2, I would consider those individuals to have low vibrant Red pigment production, and are often culled out because F3 (by interbreeding F2) resulted very bad Kohaku pattern. (to be continued...)
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AuthorDay by day, night by night, my hobby keeps surviving in limited time and space, but never stop! Categories
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September 2019
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