II. 7. A new type of trisomic for chromosome 6 (metatrisomic 6A) in barley. (1)
Junzo Fujigaki (2) and Takumi Tsuchiya, Department of Agronomy, Colorado State University, Fort Collins, Colorado 80523, U.S.A.
(1) Supported in part by USDA/SEA Competitive Research Grant 5901-0410-90334-0 to T. Tsuchiya.
(2) Visiting Associate Professor, on leave of absence from Tokyo University of Agriculture, Tokyo, Japan.
Plants which have one extra small metacentric chromosome were isolated in the F2 population from the cross, Triplo 6 x Utah T41 (CSU T35-10) (Tsuchiya and Baldivia, 1981). Frequency of the new type of trisomic is shown in Table 1. The plants are tentatively called "metacentric trisomic" or "metatrisomic" and somatic chromosome complement is designated as 2n = 14 + 1 meta 6A.
Morphological characteristics of the metatrisomic plants are difficult to describe precisely because of the hybrid condition. Therefore, to obtain a uniform genetic background the metatrisomic plants were backcrossed to Shin Ebisu 16 (SE16). Transmission rate of the metacentric chromosome was examined in the progenies of reciprocal crosses with SE16 and selfing and is shown in Table 2.
It seems from this data that the metacentric chromosome in plant No. 1 was eliminated in the course of development and not included in gametes. The extra metacentric chromosome was transmitted 25% through female gametes in plant No. 2. Transmission rate of the metacentric was higher (32%) in selfing than in the cross with SE16, but no dimetacentric plant (2n = 14 + 2 metas) was recovered. This may be due to small population size. More precise analyses are now underway to clarify the cytogenetical nature of the metacentric chromosome.
Three other metatrisomic types (metatrisomic 1A, metatrisomic 3A and 3B) have been reported (Shahla and Tsuchiya, 1979; Singh and Tsuchiya, 1981; Tsuchiya, 1972).
References:
Shahla, A. and T. Tsuchiya. 1979. A new trisomic type in the progeny of Triplo 1S. BGN 9:94-95.
Singh, R. J. and T. Tsuchiya. 1981. A balanced unstable metacentric trisomic for chromosome 3 in barley. BGN 11:68-69.
Tsuchiya, T. 1972. Cytogenetics of telotrisomics in barley. BGN 2:93-98.
Tsuchiya, T. and Ruth Baldivia. 1981. Primary trisomic analysis of an incomplete dominant zebra mutant, zbc, in barley. BGN 11:63-64.
