Two loci containing genes encoding 5S rRNA were mapped on the second a
nd third chromosomes of barley. The two gene clusters located on diffe
rent chromosomes differed in the length of the nontranscribed spacer s
eparating the 5S rRNA genes. All nontranscribed spacers contained a va
riable number of trinucleotide tandem repeats. The distribution of 5S
genes between these two clusters and their copy number varied widely b
etween cultivars and doubled haploids derived from cross between two b
arley cultivars. However, this variation had no obvious effect on plan
t phenotype.