A strongly deviating Mendelian segregation of the high-lysine gene lys3a of mutant Risø 1508 has been found in some crosses (Ahokas, 1979; Doll and Oram, 1989). The distorted segregation frequency of mutant seeds in F2 varied from 1.2% in a cross with 'Crypt' to 7.3% in a cross with 'White Naked Atlas', in contrast to the 1:3 segregation found in crosses with the parent variety 'Bomi' (Doll 1973), and with a wide spectrum of non-related varieties (Doll and Oram, 1989). A genetic explanation of the distorted segregation based on the presence of suppressor genes in some varieties was suggested by Ahokas (1978), but this has not been verified.
The distorted segregation of gene lys3a in the hybrid Risø 1508 × White Naked Atlas has now been studied among female and male gametes separately. F1 plants of the hybrid were crossed as female and male parent with a lys3a-line being different from the hybrid in alleles of the Est1 locus (Hvid and Nielsen, 1977), thus allowing a distinction between hybrid seeds and selfings. The lys3a-line derives from the cross Risø 1508 × 'Sultan' that had a normal mutant segregation.
The BCF1 seeds were scored for the mutant character by looking for shrunken opaque seed, which is an easily detectable characteristic of Risø 1508 seeds. This simple classification was verified by analysing the hordein composition of every third seed by electrophoresis (Doll and Anderson, 1981). Mutant homozygotes contain only trace amount of hordein while heterozygotes and normal homozygotes have a high hordein content, which is apparent both during hordein extraction and in the electrophoresis gel. The embryo of the seeds analyzed for hordein were germinated and analyzed for isozymes of the Est1 locus to confirm that they contained one of the alleles of the hybrid together with the allele of the lys3a-line; no seeds derived from selfing were found.
The lys3a gene segregated 1:1 among the female gametes (Table 1) as expected for a single recessive gene. A very distorted segregation was found among the male gametes, of which only 6.3% or about 1:16 contained the lys3a gene. Hence the deviating Mendelian segregation in the cross Risø 1508 × White Naked Atlas is due to a distortion factor that only influences the male gametes. The mode of action of this factor is unknown. A study of the pollen development in the hybrid did not disclose any abnormalities. The distortion factor is apparently linked with the Lys3 locus in White Naked Atlas, because no lines segregating a corresponding surplus of mutant seeds were found among the F2-lines studied earlier (Doll and Oram, 1989). The presence of the same factor in other varieties showing deviating segregations of mutant seeds when crossed with Risø 1508 is indicated by the results of Ahokas (1988). He also reported a 1:1 segregation when the hybrid Crypt/1508 was pollinated by mutant 1508.
A study of the influence of the distortion factor on the segregation of genes linked with lys3a has been initiated.
Ahokas, H. 1978. Genetic suppression of shrunken endosperm in Risø mutant 1508. Barley Newsl. 21:62-64.
Ahokas, H. 1979. Further results on the suppression of shrunken endosperm in hiqh lysine mutants. BGN 9:3-7.
Ahokas, H. 1988. High-lysine gene segregation distorted in the barley cross Risø 1508 × Crypt CI 1090: Patterns of endosperm proteins by an electrophoretic method. Hereditas 108:129-131.
Doll, H. 1973. Inheritance of the high-lysine character of a barley mutant. Hereditas 74: 29B - 294.
Doll, H., and B. Andersen. 1981. Preparation of barley storage protein, hordein, for analytical sodium dodecyl sulfatepolyacrylamide gel electrophoresis. Analytical Biochemistry 115:61-66.
Doll, H., and R. Oram. 1989. Deviating Mendelian segregation of barley gene lys3a. Hereditas 110:97-99.
Hvid, S., and G. Nielsen. 1977. Esterase isoenzyme variants in barley. Hereditas 87:155-162.