The female-killing chromosome of the silkworm, Bombyx mori, was generated by translocation between the Z and W chromosomes.
Bombyx mori is a female-heterogametic organism (female, ZW; male, ZZ) that appears to have a putative feminizing gene (Fem) on the W chromosome. The paternally transmitted mutant W chromosome, Df(p ( Sa ) + ( p )W + ( od ))Fem, derived from the translocation-carrying W chromosome (p ( Sa ) + ( p )W + ( od )), is inert as femaleness determinant. Moreover, this Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome has been thought to have a female-killing factor because no female larvae having the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome are produced. Initially, to investigate whether the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome contains any region of the W chromosome or not, we analyzed the presence or absence of 12 W-specific RAPD markers. The Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome contained 3 of 12 W-specific RAPD markers. These results strongly indicate that the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome contains the region of the W chromosome. Moreover, by using phenotypic and molecular markers, we confirmed that the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome is connected with a partially deleted Z chromosome and that this fused chromosome behaves as a Z chromosome during male meiosis. Furthermore, we demonstrated that the ZZW-type triploid female having the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome is viable. Therefore, we concluded that the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome does not have a female-killing factor but that partial deletion of the Z chromosome causes the death of the ZW-type diploid female having the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome. Additionally, our results of detailed genetic analyses strongly indicate that the female-killing chromosome composed of the Df(p ( Sa ) + ( p )W + ( od ))Fem chromosome and deleted Z chromosome was generated by translocation between the Z chromosome and the translocation-carrying W chromosome, p ( Sa ) + ( p )W + ( od ).
Fujii
T
T
Department of Biological Production, Faculty of Agriculture, Tokyo University of Agriculture and Technology, Saiwai-cho 3-5-8, 183-8509, Fuchu, Tokyo, Japan.
Tanaka
N
N
Yokoyama
T
T
Ninaki
O
O
Oshiki
T
T
Ohnuma
A
A
Tazima
Y
Y
Banno
Y
Y
Ajimura
M
M
Mita
K
K
Seki
M
M
Ohbayashi
F
F
Shimada
T
T
Abe
H
H
D000818:Animals; D017849:Animals, Inbred Strains; D012831:Bombyx / Q000196:embryology / Q000235:genetics*; D019457:Chromosome Breakage; D002872:Chromosome Deletion; D004531:Eggs; D005260:Female; D005262:Feminization / Q000235:genetics; D005804:Genes, Lethal; D005819:Genetic Markers; D005838:Genotype; D008297:Male; D012150:Polymorphism, Restriction Fragment Length; D011123:Polyploidy; D012727:Sex Characteristics; D012729:Sex Chromosome Aberrations; D012732:Sex Determination Analysis; D016019:Survival Analysis; D014178:Translocation, Genetic / Q000502:physiology*
D005819:Genetic Markers