The pattern of mutation of an unstable gene in Delphinium ajacis

Abstract

1. Inheritance of flower colour in Delphinium ajacis is controlled by a locus with three stable alleles: pb (blue) is dominant to pl (lavender), which is dominant to p (pink). An unstable allele, p*, exists in a number of states, distinguished by the pattern of their mutation to pb and p during the development of the sepals.2. The rate of occurrence of blue sectors and spots in the developing sepals of p*p* plants is twice that in the sepals of p*pl plants. The rate of mutation to pb apparently falls during the development of the sepals and this is probably due to p* mutating also to the stable p allele.3. The frequency of pb and p gametes from p*p* plants is twice that from p*pl plants.4. The pb mutants from p* show no evidence of instability; the controlling element has transposed from the locus.5. Some p mutants from p* are apparently stable; others can reacquire instability, especially during sexual reproduction. The latter are tentatively interpreted as due to transpositions of the controlling element to other sites within the gene.6. The instability of p* is only shown in the presence of a dominant activator.7. Evidence is presented of transposition of the controlling element from p* to a locus controlling the colour of the foliage.