II. 12 Linkage of shrunken endosperm mutant sex 1 and male sterile mutant msg, , bk on chromosome 6 of barley.
C. A. Foster, Welsh Plant Breeding Station, Aberystwyth, Wales, G. B.
A shrunken endosperm mutant inherited as a monofactorial recessive expressing xenia, described by Jarvi and Eslick (1971), was designated se 6 and assigned to chromosome 6 (Jarvi, 19709. It was subsequently redesignated sex 1 (Eslick and Hockett, 1976) in order to distinguish shrunken endosperm genes expressing xenia from those which do not.
Male sterile genes msg 6 and msg, , bk have also been assigned to chromosome 6 (Hockett, 1971; Eslick, Ramage and Clark, 1974).
The following linkage estimate between sex 1 and msg, , bk was obtained in 1976. F2 progenies of 8 F1 repulsion heterozygotes (Msg, , bk sex 1/msg, , bk Sex 1) were grown, progeny sizes ranging from 59 to 120 and totalling 625 plants. The analysis of X2 for observed against a 9 : 3 : 3 : 1 expectation (Table 1), confirms the single gene segregations and that the families were homogeneous. The X2 for linkage was significant and again the families were homogeneous.
Table 1. Summary of chi-square analysis of eight F2 families segregating for ms, , bk and sex 1.
The xenia expression of the shrunken endosperm gene permitted separation of normal and shrunken seed prior to sowing, allowing identification and distinction of the male fertiles which were homozygous for Sex from the heterozygotes Sex sex, thus providing a no-linkage expectation of five classes instead of the usual four, i.e,, a 3 : 6 : 3 : 3 : 1 ratio instead of a 9 : 3 : 3 : 1 ratio. The observed segregation was:
9 MS_Sex Sex : 301 Ms_Sex sex : 152 Ms Ms xex sex:
160 ms ms Sex Sex : 3-ms ms sex sex
The linkage estimate obtained from this F2 data, by the maximum likelihood method, was p = 0.047 + 0.012, i.e., a recombination value of 4.7% + 1.2%.
This estimate corresponds closely with that made by Eslick and Ries (1976) based on F3 data, namely 5.6% + 1.0%. Both estimates place these two genes considerably closer than suggested by Kasha (1976).
It is interesting to note that without the separation of the two genotypic classes within the fertile class the linkage estimate based on the usual 9 : 3 : 3 : 1 expectation would have been 148 + 3.9%, considerably less accurate. With the partial classification of the F2 being possible, F3 data would not be expected to provide a better estimate than the 4.7% obtained (Allard, 19562,
References:
Allard, R. W. 1956. Formulas and tables to facilitate the calculation of recombination values in heredity. Hilgardia 24, 235-278*
Eslick, R. F. and E. A. Hockett. 1976 Description of shrunken endosperm mutant sex 1. BGN 6, 140.
Eslick, R. F., Ramage, R. T., and D. R. Clark. 1974 Two genetic male steriles, msg 6 and msg, , bk assigned to chromosome 6. BGN 4,
Eslick, R. F. and M. N. Ries. 1976. Positioning sex 1 on chromosome 6. BGN 6, 21-22.
Hockett, E. A. 1971. Description of male sterile mutant ms 6. BGN 1, 178-179.
Jarvi, A. J. 1970. Ph.D. Thesis. Montana State University, Bozeman, Montana.
Jarvi, A. J. and R. F. Eslick. 1971. Description of shrunken endosperm mutant se 6.
Kasha, K. J. 1976. Chromosome 6 co-ordinator's report, BGN 6, 100
