Evolutin of fraction I protein in relation to origin of amphidiploid Brassica species and other members of the Cruciferae

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Abstract
Fraction I proteins contained in 14 species representing five genera of Cruciferae were analyzed by isoelectric focusing. Two types of large subunit polypeptides whose isoelectric points are coded by extranuclear DNA and four different small subunit polypeptides coded by nuclear DNA were identified. One small subunit polypeptide was found only in Sinapsis arvensis; the remaining three were distributed among the 13 other species. No correlation was discernible between fraction I protein composition and relatedness between the 14 species as determined by the cytogenetic analysis of Mizushima6 Fraction I protein composition of three alloploid Brassica species whose diploid progenitors had been determined showed that multiple small subunit polypeptides arise by allopolyploidy wherein the amount of each polypeptide in the alloploid is approximately one-half that contained in the parent. The results also showed B. nigra to have been the female partner with B. oleraceae in the genesis of B. carinata and the male partner with B. campestris in the genesis of B. juncea. Absence of a difference in large subunit polypeptides between B. oleraceae and B. campeslris disallowed determination of which species was the female in the genesis of B. napus.