II.33 Trisomic analysis of grandpa 2 (gp2).
T. Tsuchiya, Agronomy Department, Colorado State University, Fort Collins, Colorado 80521, U.S.A.
Walker et al. (l963) reported the results of inheritance and linkage
studies of a grandpa-type mutant induced in the variety, Montcalm. Their
results indicated that the grandpa gene (gp2) showed linkage with
orange lemma gene (o) on chromosome 6 with crossover value of 38.0
+ 3.7. Later, Matchett (1968, Ph.D. Thesis, Colo. State Univ.) found
from allelism test that gp2 was allelic to the previously designated
grandpa gene (gp) which was located at the distal part of chromosome
2 (Matchett, 1968; Robertson, 1971). A trisomic test was made to solve
this problem of conflict on the association of gp2 and its chromosome
with the use of primary trisomic for chromosome 6 (Purple) and telotrisomic
for chromosome 2L. The segregating ratio of normal green vs. grandpa in
F2 from crosses between Purple and gp2 fitted well to the disomic
ratio of 3:1 (X2 = 0.023, p = 0.90-0.80) with appreciable frequency
of recessive homozygotes in the trisomic portion. In the F2 population
from the cross between 2x + 1 telo 2L and gp2 stock, the segregating
ratio did not fit the disomic ratio (X2 = 12.83 with very small
p value). The segregating ratio fits, however, a 7:1 (X2 = 2.13
and p = 0.20-0.10). These results clearly showed that the gp2 gene
is not carried by chromosome 6 but located on the long arm of chromosome
2. All 45 F1 plants from reciprocal crosses between grandpa (gp)
and grandpa 2 (gp2 ) showed typical grandpa characters in agreement
with the results obtained by Matchett (1968). This finding strongly suggests
the importance of an allelism test before the linkage analysis of a new
mutant is made. The effectiveness of trisomic analysis in associating a
gene with its respective chromosome or chromosome arm was also demonstrated.
Reports II.29 (P. 58) through II.39 (P. 66) by T. Tsuchiya and coworkers are based on the results of researches supported partly by NSF Research Grant GB 4482 X.