II.26. Linkage between the loci Amy1 (alpha-amylase), o (orange lemma) and xn (xantha seedling).
Gunnar Nielsen and Ove Frydenberg, Danish Atomic Energy Commission Research Establishment Risø DK-4000 Roskilde, and Department of Genetics, University of Aarhus, DK-8000 Arhus C, Denmark.
Linkage between the alpha-amylase locus Amyl and the orange lemma locus, o, which is located on chromosome 6, has been reported previously (Nielsen and Frydenberg, 1971). The linkage relation between Amyl, o, and xn has now been investigated in a three point test from the following cross:
Amy1Bi/Amy1Bi, O/O, Xnn/xn (female) x Amy1Ke/Amy1Ke, o/o, Xn/Xn (male)
The genes o and xn are recessive and plants homozygous for xn die at the seedling stage. The amylase alleles are codominant and homozygotes as well as heterozygotes can be identified on the germinating F2 seeds including the xn/xn seeds. Since the homozygous xn plants cannot be classified for orange lemma the F2 analysis was complemented with F3 plants to identify more of the F2 genotypes.
The F2 segregation, shown in Table 1, yielded the following recombination percentages:
Amy1 - o r = 24.9 + 2.6
Amy1 - xn r = 19.7 + 2.3
xn - o r = 6.1
+ 1.5
The observed numbers of plants are in good agreement with the expected numbers calculated from the estimated recombination values (X2 = 10.0 d.f. = 17).
The order of the loci is obviously o - xn - Amy1 and, according to the positions of o and xn given in BGN 3:102, this means that Amy1 is located on the long arm of chromosome 6.
Attention is called to the fact that the amylase gene symbols have been changed in order to agree with the nomenclature rules. Amy1Bi = Amy (BGN 1:34) = alpha-amyC (Frydenberg et al. 1969); Amy1Ke = amy = alpha-amyC1.
Table 1. Observed and expected (in brackets) numbers of F2 plants.
References:
Frydenberg, O., G. Nielsen and J. Sandfaer. 1969. The inheritance and distribution of a-amylase types and DDT responses in barley. Z. Pflanzenzuchtung 61:201-215.
Nielsen, G. and O. Frydenberg. 1971. Linkage between the loci orange lemna and amy. - BGN 1:34.
