Genetic instability of anthocyanin production in Impatiens balsamina

Summary It is established that in a naturally occurring variegated Impatiens balsamina the phenotype is determined by a mutable allele p^m, of an anthocyanin-governing gene P^r. The special allele produces an acyanic phenotype like the stable recessive p but undergoes frequent changes to P^r in somatic and germinal cells (causing a variegated phenotype in the former) when a controlling element M is also present in the genome. It is suggested that p^m is a repressed p^r and M acts either by removing or inactivating whatever causes that repression. Such changes proceed in a unique fashion: either p^m changes to p^r or to an intermediate labile condition P which then changes to p^r, resulting either in dark or pale, or dark super-imposed on pale, sectors; a reverse situation was not observed. Colourless plants which occasionally appear in unstable lines seem to be due to loss of M although changes ofp^m itself cannot be ruled out at present.