No abstract

Lodging is a major constraint to increasing yield in many crops, but is of particular importance in the small-grained cereals. This study investigated the genetic contro! of lodging and component traits in wheat through the detection of utiderlying quantitative trait loci (QTL), The analysis was based on the identittcation of genomic regions which affect various traits related to lodging resistance in a population of 96 doubled haploid lines of the cross 'Milan' x 'Catbird", mapped using 126 microsatellite markers. Although major genes related to plant height (Rhl genes) were responsible for increasing lodging resistanee in this cross, several other traits independenl of plant height were shown to be important such as rool and shoot traits, and various components of plant yield. Yield components sueh as grain number and weight were shown to be an indicator of plant susceptibility to lodging-QTL for lodging and associated traits were found on chromosomes IB, ID. 2B. 2D. 4B, 4D. 6D and 7D. QTL for yield and associated traits were identified on chromosomes IB, ID. 2A. 2B. 2D. 4D and 6A,

The genetic basis of variation in complex traits remains poorly understood, and few genes underlying variation have been identified. Previous work identified a quantitative trait locus (QTL) responsible for much of the response to selection on growth in mice, effecting a change in body mass of approximately 20%. By fine-mapping, we have resolved the location of this QTL to a 660-kb region containing only two genes of known function, Gpc3 and Gpc4, and two other putative genes of unknown function. There are no non-synonymous polymorphisms in any of these genes, indicating that the QTL affects gene regulation. Mice carrying the high-growth QTL allele have approximately 15% lower Gpc3 mRNA expression in kidney and liver, whereas expression differences at Gpc4 are non-significant. Expression profiles of the two other genes within the region are inconsistent with a factor responsible for a general effect on growth. Polymorphisms in the 3′ untranslated region of Gpc3 are strong candidates for the causal sequence variation. Gpc3 loss-of-function mutations in humans and mice cause overgrowth and developmental abnormalities. However, no deleterious side-effects were detected in our mice, indicating that genes involved in Mendelian diseases also contribute to complex trait variation. Furthermore, these findings show that small changes in gene expression can have substantial phenotypic effects.

sue culture medium manipulations (Comeau et al., 1992;Suenaga, 1994;Kammholz et al., 1996). The genotypic A number of maize (Zea mays L.) genotypes were tested for their specificity became evident gradually, more as a result influence on induction and regeneration of haploid wheat (Triticum aestivum L.) embryos to improve further the efficiency of the wheat ϫ of a consensus emerging from several studies with varied maize system of haploid production. Fifteen maize genotypes were objectives than from a direct investigation of this phecrossed to five diverse wheat F 1 hybrids in a line ϫ tester fashion in nomenon. As a consequence of this situation, very few three replications. Two efficiency parameters, caryopses formation studies address this problem systematically, e.g., the gefrequency (CFF-number of caryopses/100 pollinated florets) and notypic specificity of only the maize or only the wheat embryo formation frequency (EFF-number of embryo-carrying carygenotypes was studied, the data was either based on a opses/100 pollinated florets), were estimated. Analysis of variance single replication (Suenaga and Nakajima, 1989; Laurie revealed that lines (wheat genotypes), testers (maize genotypes), and and Reymondie, 1991; Ushiyama et al., 1991; Amrani their interaction showed significant effects on both efficiency parameet al. Sarrafi et al., 1994;Suenaga, 1994; ters, but the effect of maize genotypes was greater than that of wheat al., 1995), or the study was based on only a few parents