The darts target the genes that determine the most interesting and obvious differences between barley varieties. These genes determine morphological traits - things we can see with our eyes. No genetics labs required. In this example, we are showing two of the possible visible manifestations (phenotypes) of each of these genes (e.g. Blp, Vrs1, etc.) None of these genes have yet been cloned so we do not know the differences in DNA sequence (genotype) that lead to the differences in phenotype.
The two forms of each trait that we illustrate are present in the two parents of the Oregon Wolfe Barley population. In the population of 94 plants derived from this cross, one sees predicted patterns of Mendelian segregation and independent assortment of the dominant and recessive alleles at these morphological trait loci.
There are different genetic mechanisms that can lead to dominant and recessive alleles, but one of the simplest is a loss of function of the gene due to the loss or gain of DNA nucleotides. If the gain or loss of DNA changes important coding or regulatory regions of the dominant form of the gene, this can result in a different gene product, or no gene product. This altered or different product leads to the recessive) phenotype.
Genetic differences are essential for evolution and for genetic analysis. These difference arise through mutation, which occurs naturally. Mutations can also be induced in various ways. Since only very few of the thousands of genes in an organism show striking morphological differences like those illustrated in the dartboard, geneticists have found other ways to create genetic variation.
One powerful tool for creating genetic variation is called transposon tagging. This involves harnessing the Ac and Ds transposons of corn to tag genes in other species. The concept is simple - if the transposon inserts in a gene, it will alter the gene and based on this change, the gene can be isolated. The isolation is possible due to the fact that the sequence of the transposons is known and serves as a tag for retrieval of the gene sequence.
With support from the National Science Foundation, we have transferred the Ac and Ds transposons to barley and we are tracking their movement through the barley genome. We have mapped these insertion sites (Cooper et al) and these sites are shown on the dartboard as Dst loci. For more information on each of the Dst loci, please visit Transposon-Mediated Functional Genomics in Barley, hosted by GrainGenes.
Unfortunately, none of the Ds transposons have landed in any of the morphological genes - causing a visible change from dominant to recessive. Most of the transposons have landed in genes that we do not yet know very much about and we are currently studying the effects of these insertion events.
So stay tuned - as we characterize changes in gene function due to Ds insertion, these results will appear on the dartboard.