M chromosome of the wild silkworm, Bombyx mandarina (n = 27), corresponds to two chromosomes in the domesticated silkworm, Bombyx mori (n = 28).
Chromosomes of Bombyx mori (n = 28) and of Bombyx mandarina (n = 27) were studied cytogenetically to resolve the origin of the large M chromosome in the Japaneses type of B. mandarina. In the F1 progeny from the reciprocal cross between B. mandarina and B. mori, the mitotic chromosome number was 2n = 55, and a chromosome configuration of 26 bivalents plus 1 trivalent was observed at metaphase I of germ cells. The trivalent chromosome consisted of the M chromosome from B. mandarina and two chromosomes from B. mori. When males of B. mori were mated to the F1 females, nuclei with two types of chromosome number (2n = 55 and 2n = 56) and two sets of chromosome pairs (26 bivalents plus 1 trivalent versus 28 bivalents) were observed in the metaphase I stage. Linkage analysis showed that the 14th chromosome of B. mori was involved in these two types of chromosome segregation. This result indicates that the M chromosome in B. mandarina arose from a fusion between a chromosome corresponding to the 14th linkage group and another, yet unidentified linkage group.
Banno
Yutaka
Y
Institute of Genetic Resources, Kyushu University Graduate School of Bioresource and Bioenvironmental Sciences, Fukuoka, Japan. banno@agr.kyushu-u.ac.jp
Nakamura
Takashi
T
Nagashima
Eiichi
E
Fujii
Hiroshi
H
Doira
Hiroshi
H
D000818:Animals; D012831:Bombyx / Q000235:genetics*; D002874:Chromosome Mapping; D020090:Chromosome Segregation / Q000235:genetics*; D002875:Chromosomes / Q000235:genetics*; D003433:Crosses, Genetic; D007564:Japan; D007621:Karyotyping