The silkworm, Bombyx mori, is domesticated lepidopteran insect (moths and butterflies) which has been scientifically and practically used for a long time. Sex-limited yellow cocoon (Sy) strain was induced by γ-irradiation in order to discriminate male cocoons from females. The W chromosome has been believed to be translocated a long fragment of chromosome 2 carrying yellow blood (Y) gene locus. Our BAC-FISH analysis of the Sy female revealed the W mutation consists of not only chromosome 2 but also chromosome 24 with reciprocal translocation. The female sex chromosomes and the partners (designated as W1, W2, Z, S2S24, Chr2 and Chr24) forms a hexavalent during meiosis. Because of normal karyotype in Sy males the sex chromosome constitution (major type, 2n=56) can be considered to be kept by the hexavalent formation and its segregation.
We noticed a few male individuals of the Sy descendant whose growth are delayed with smaller body size in the final achievement. Real-time quantitative PCR (qPCR) demonstrated that 30 among 33 males have only single copies in wide range of chromosome 2 genes tested (approx. 1.5Mb to the end). We also found 3 males were fully single copy carrier of the chromosome 2 genes tested. One of the males (Syr6) was crossed with a p50 (+p/+p) female. The phenotype of hybrid larvae (p50Syr6) segregated to +p : pS = 1 : 1 in the both sexes. Further cross of the +p males to p53 (pY/pY) females segregate to +pY and pY phenotypes with 1 to 1 ratio. Similar qPCR analyses revealed that former +p and the latter pY individuals have single copies of the chromosome 2 genes tested. Hence we suppose that the Syr6 and the descendants are autosomal monosomy that is the second case in animals after 97-years-ago discovery in Drosophila melanogaster.
The silkworm, Bombyx mori, is domesticated lepidopteran insect (moths and butterflies) which has been scientifically and practically used for a long time. Sex-limited yellow cocoon (Sy) strain was induced by γ-irradiation in order to discriminate male cocoons from females. The W chromosome has been believed to be translocated a long fragment of chromosome 2 carrying yellow blood (Y) gene locus. Our BAC-FISH analysis of the Sy female revealed the W mutation consists of not only chromosome 2 but also chromosome 24 with reciprocal translocation. The female sex chromosomes and the partners (designated as W1, W2, Z, S2S24, Chr2 and Chr24) forms a hexavalent during meiosis. Because of normal karyotype in Sy males the sex chromosome constitution (major type, 2n=56) can be considered to be kept by the hexavalent formation and its segregation.
We noticed a few male individuals of the Sy descendant whose growth are delayed with smaller body size in the final achievement. Real-time quantitative PCR (qPCR) demonstrated that 30 among 33 males have only single copies in wide range of chromosome 2 genes tested (approx. 1.5Mb to the end). We also found 3 males were fully single copy carrier of the chromosome 2 genes tested. One of the males (Syr6) was crossed with a p50 (+p/+p) female. The phenotype of hybrid larvae (p50Syr6) segregated to +p : pS = 1 : 1 in the both sexes. Further cross of the +p males to p53 (pY/pY) females segregate to +pY and pY phenotypes with 1 to 1 ratio. Similar qPCR analyses revealed that former +p and the latter pY individuals have single copies of the chromosome 2 genes tested. Hence we suppose that the Syr6 and the descendants are autosomal monosomy that is the second case in animals after 97-years-ago discovery in Drosophila melanogast ...
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