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An analysis of the α-amylase isozymes in GA-treated endosperm of wheat nullisomic-tetrasomics shows that there is more variation at the α-Amy-1 and α-Amy-2 homoeoallelic loci than was previously thought. Among the 16 isozymes produced by genes on the group 7 chromosomes, most could be definitely established as products of a single homoeoallele.Inter-varietal allelic differences would be expected at such loci and clear variation was found in isozymes produced by chromosomes 6B and 7B. The latter allele, α-Amy-B2b carried by the variety 'Hope', was used to locate the enzyme structural gene within chromosome 7B relative to the centromere and five other gene markers.The nature of the α-Amy-B2b phenotype and the rare non-parental isozyme patterns found among the recombinant lines indicates that the locus is large and compound, probably involving some degree of intra-locus gene duplication.

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SUMMARYAnalysis of glucose phosphate isomerase (GPI) zymograms extracted from grains of wheat aneuploids indicated that the three Gpi-1 loci each control the production of at least two enzyme subunits. Flat bed isoelectric focussing revealed the 21 possible GPI dimers as 11 discrete bands.Although no varietal differences were detected in the Gpi-1 products, a null-allele at the Gpi-D 1 locus was found in some stocks of Chinese Spring.Analysis of crosses segregating for this Gpi-D lb phenotype indicated that the genes encoding the enzyme subunits are closely linked and comprise a compound locus.GPI zymograms were used to identify homoeologous loci in chromosome additions of rye and Hordeum chilense to wheat, and to confirm the genotypes of chromosome substitutions of Aegilops umbellulata in wheat.

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SUMMARYDetectable allelic variation at the Gpi-1 loci on the short arms of the homoeologous group 1 chromsomes in wheat is not common. However, a variant null allele at the Gpi-D1 locus is present in some stocks of Chinese Spring. This has allowed the locus to be mapped between the ω-gliadin locus carried distally on the short arm of chromosome 1D, Gli-D1 (34·5%) and the high-molecular-weight glutenin subunit locus carried near the centromere on the long arm, Glu-D1 (36·2%). The origin of this isoenzyme polymorphism in Chinese Spring stocks is described and its potential significance is discussed in relation to quantitative analysis of aneuploids, alien chromosome addition and substitution lines and intervarietal chromosome substitution lines involving Chinese Spring.

The reciprocal monosomic analysis (RMA) technique of intervarietal chromosome manipulation was used to investigate the genetic control of grain weight in two varieties of wheat (Spica and Chinese Spring). The method enabled major genetic differences between the two varieties for this quantitative character to be assigned to individual chromosomes.The RMA was extended by the extraction of reciprocal disomic F3 families, of which individual ears were analysed at maturity for grain weight at each position within the ear. Chromosomes 1A, 1D and 7A of the large-grained parent, Spica, increased grain weight relative to the homologous chromosomes of the small-grained parent, Chinese Spring. The effect of chromosomes 1D and 7A were proportionately similar throughout the ear, while that of 1A was disproportionately greater in the distal fiorets of each spikelet. None of these differences involved simultaneous effects on grain number and thus could be considered to be specific genetic effects on grain growth. INTRODUCTIONA conventional biometrical analysis of the genetic differences between two varieties of wheat (Triticum aestivum, 2n = 6x = 42) is often unsuitable for the identification of genes with major effects on quantitative characters because many genes are likely to be involved and their individual effects cannot be distinguished. Furthermore, in the case of grain weight at maturity, it is usually not possible to separate competitive effects on grain weight due to differences in grain number per ear from direct effects on grain development. Even varieties having the same mean number of grains per ear may have different numbers of spikelets and grain-bearing fiorets per spikelet, which can confuse the interpretation of genetic differences in grain weight.However, methods of genetic analysis involving intervarietal chromosome manipulation can be used to separate the effects of each chromosome of the genome so that the major chromosomal effects on a particular character can be identified. These methods range from the relatively simple, such as conventional F1 or F2 monosomic analysis (Sears, 1953; Kuspira and Unrau, 1959) sophisticated but labour-intensive, such as development and analysis of intervarietal chromosome substitution lines (Kuspira and Unrau, 1957;Law, 1967). The choice of method depends on the nature of the character being studied (qualitative or quantitative), the availability of appropriate aneuploid lines and the time and effort that it is practical to spend on the analysis.The method used here was that of reciprocal monosomic analysis, first described and used by McEwan and Kaltsikes (1970) and subsequently by Law et al. (1979;1981). It enables the detection and chromosomal location of allelic differences between two varieties by comparing the effects of each chromosome in one variety with those of its reciprocal homologous chromosome in the other variety. In addition to the identification of large genetic effects on grain weight, it was possible to overcome the problems of interpretation caused by...