• D. H. Long

      Articles written in Journal of Genetics

    • The inheritance of colour in diploid potatoes - I. Types of anthocyanidins and their genetic loci

      K. S. Dodds D. H. Long

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      Two independent loci are shown to be concerned with the development of certain anthocyanin pigments throughout the plant body of diploid cultivated potatoes. A third locus is epistatic to these in its homozygous recessive phase and suppresses the development of pigment in the tuber only.

      One pigment locus, designatedP, governs the occurrence of an acylated glycoside of petunidin in tuber, sprout and flower, and in this respect corresponds to the ‘wild-type’ locus of wild tuberous species in which the same derivative of petunidin occurs alone.

      Two alleles of the other pigment locus, designatedR, are identified and are hypostatic toP. The dominant,R, in the absence of P, has a dual effect: an acylated glycoside of pelargonidin occurs in the tuber and sprout only, and a glycoside of cyanidin in the flower only. Epistasy is incomplete in the flower where the glycoside of cyanidin occurs also in the presence ofP. These multiple effects are inseparable in heredity. In individuals homozygous for the recessivePpw, and in the absence ofP, these pigments do not occur.

      An acylated derivative of peonidin occurs in all cultivated diploids, and in consequence no conclusions can be drawn about its inheritance. This anthocyanin is suppressed in the flowers only of genotypes homozygous forRpw. The suggestion is made that further search might reveal an alleler which in the homozygous phase and in the absence ofP would be expected to suppress all pigments, at least in tubers and flowers.

      Types of anthocyamdins other than petunidin occur only in cultivated potatoes but are similar in diploids and tetraploids. Presumably, this variability has been established by human selection at the diploid level and the evolution of tetraploidy was a later event in the genetic history of cultivated potatoes.

    • The inheritance oe colour in diploid potatoes II. A three-factor linkage group - With one text-figure

      E. S. Dodds D. H. Long

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      o| li]1.|Three loci,B, I andF, concerned with the distribution of anthoeyanins in diploid cultivated potatoes, are identified. AllelesBd>Bc>Bb>Ba>b, in order of dominance, are distinguished.

      Bd produces in the seed a band of pigment on the node of the hypocotyl of the embryo and, in the mature plant, a band of pigment at each node, a coloured floral abscission layer and a coloured eyebrow on the tuber.

      WithBc, a band of pigment at each node of the mature plant is absent, but other effects are like those ofBd.

      Bb gives a coloured floral abscission layer and a coloured eyebrow on the tuber. WithBa only the floral abscission layer is coloured.

      LocusI in its homozygous recessive phase,ii, inhibits pigment in the tuber.

      LocusF in its homozygous recessive phase,ff, gives flecked flowers. li]2.|The three loci are closely linked and probably in the orderB-I-F. li]3.|Bc andI, in coupling, give a positional effect so that the characteristic nodal bands ofBd occur. LocusB appears to be a super-gene. li]4.|The suggestion is made that the proximity of these loci is original and functional. It may facilitate intergenic co-operation in the distribution of pigment.

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