One of the genetic phenomena of silkworm. Cocoons are divided into white cocoons and colored cocoons, and colored cocoons are divided into two types: yellow cocoon and green cocoon.
Yellow cocoons
Yellow cocoons have golden, light yellow, ligustic, flesh-colored, light red and other cocoon colors. Common white cocoons are recessive to colored cocoons, but some varieties of European white cocoons are dominant to yellow cocoons and are called dominant white cocoons. Generally speaking, the yellow blood of the yellow cocoon silkworm is yellow blood, and the white cocoon silkworm blood is colorless, but the yellow blood white cocoon silkworm is found because it is known that the yellow cocoon and yellow blood are controlled by different genes. The golden cocoon gene (C) must be complementary to the yellow blood gene (Y) to show the outer golden color. The ligustic cocoon (C st ) and the inner yellow cocoon (C I ) must complement Y in order to appear. If it doesn’t combine with Y, it becomes a white cocoon. C st and CI are not completely dominant to the white cocoon gene (+ c ). The dominant white cocoon is due to the yellow blood suppressor gene (I) that makes Y not yellow. In addition, the coal element white cocoon gene (I s) Also prevents various cocoon colors from becoming white cocoons. The flesh-colored cocoon gene (F) must also coexist with Y to appear flesh-colored. The light red cocoon gene (PK) has to be combined with Y and F to show the light red cocoon color. The inner layer of both color cocoons is white. It has been found that the cocoon pigment of the yellow cocoon series comes from mulberry leaves. Carotene-like pigments in mulberry leaves (with β-carotene, new-bearing-β-carotene, lutein, dandelion xanthin, violaxanthin, and bacteroxanthin) after being ingested by silkworms It enters the blood through the wall of the midgut, and then enters the liquid silk material through the silk gland cells, and finally the silk cocoon appears different types of cocoon colors. Y can allow the pigment to enter the blood through the midgut membrane, but +Y cannot. When I or Is and Y exist together, the Y pigment cannot penetrate the midgut wall. Some people also explain the results of the decomposition of the pigment. It is also believed that in individuals with I or Is, the basement membrane of the midgut prevents the passage of pigment. A new gene, Acp, was found to modify the inhibitory function of I. When Acp and YIC coexist, the blood is not white but pale yellow. F is related to the permeability of carotene to silk gland cells, and C is related to the permeability of lutein. Y allows the pigment to penetrate the midgut epithelium and silk gland cells, and only the silk glands with YC genotype can take up various carotenoid pigments from body fluids. I does not inhibit the silk gland cells of individuals with YC genotype from uptake of pigment from the blood, but it can prevent the pigment from spreading from the silk gland cells to the liquid silk material. The difference in coloring between the inner and outer layers of the cocoon, such as golden outer color and inner white color, outer flesh color and inner white color, is due to the different pigment permeability of different parts of the silk gland, which is determined by the control of various genes. Conclusions made by gland transplantation experiments.
Green cocoons
Green cocoons have various concentrations of green cocoons and light bamboo color cocoons. The Bilian and Dazoo native to China are typical green cocoons. The progeny of the cross between the Chinese white cocoon species and the Japanese white cocoon species often produce light bamboo-colored cocoons, which are called Sasame cocoons in Japan. Light bamboo color cocoons have two genes, Ga and Gb, each of which appears white when they exist alone. Through hybridization, the two genes complement each other to produce light bamboo color. Another independently inherited Gc gene produces green cocoons with a stronger color, which is dominant to white cocoons. Green cocoon pigment is a flavonoid, and the bombycin synthesized in silkworms is not found in mulberry leaves. Ga enables midgut cells to synthesize green cocoon pigment, and silk gland cells also have pigment permeability, but the pigment cannot enter the blood through midgut epithelium cells, so the cocoon is white. Gb enables the midgut cells and blood to synthesize green cocoon pigment. The pigment can also pass through the midgut cells into the blood, but cannot pass through the silk gland cells from the blood, so it is also a white cocoon. The two complement each other, so that the pigment finally enters the silk gland cavity and a light green cocoon appears. The green cocoon pigment was extracted by paper chromatography. There are 7 yellow-green fluorescent spots and 2 yellow-brown fluorescent spots on the chromatogram. Five of them belong to flavonoids and four are flavonoid analogues. Green cocoon varieties contain these 9 pigments in the blood and in the cocoon layer. Although there are 9 pigments in the blood of light bamboo cocoons, the cocoon layer contains only 7 yellow-green fluorescent pigments, but not the other two yellow-brown fluorescent pigments in green cocoons. Green cocoon pigment is distributed in all silk materials, and it is abundant in green cocoons, even in yellow cocoons. Some studies have shown that green cocoon pigments are contained in various cocoons.
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