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Genetic and Biochemical Consequences of Polyploidy in Tragopogon
M. L. Roose and L. D. Gottlieb
Vol. 30, No. 4 (Dec., 1976), pp. 818-830
Published by: Society for the Study of Evolution
Stable URL: http://www.jstor.org/stable/2407821
Page Count: 13
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The tetraploid species of Tragopogon, T. mirus and T. miscellus, are the only unambiguous examples of the recent natural origin of allotetraploid plant species. Both species originated during the present century and it is likely that their genomes have undergone little or no modification since their origin: T. dubius × T. porrifolius gave rise to T. mirus, and T. dubius × T. pratensis to T. miscellus. Thus, the two tetraploid species provide critical evidence regarding the initial genetic and biochemical consequences of allotetraploidy. Electrophoretic analysis of variation in 13 enzyme systems specified by a minimum of 21 genes revealed that the three diploid species are monomorphic or nearly so for different alleles at about 40% of their genes, a result fully concordant with their sharp morphological separation. The combination of these divergent diploid genomes to form the tetraploid species has provided them with substantial phenotypic heterozygosity. Thus, T. mirus has a fixed heterozygous multi-enzyme phenotype specified by 43% of its 21 duplicated genes examined and T. miscellus is similarly heterozygous at 33% of its genes. In contrast, very few individuals in the diploid species were heterozygous at even a single gene. Every one of the enzymes detected in each tetraploid species was fully accounted for by simple additivity of polypeptide subunits specified by alleles inherited from its diploid parents. The tetraploids also express novel heteromeric enzymes not produced in either one of their parents. The observed patterns of additivity in both tetraploid species fully confirm their ancestry as documented by Ownbey (1950). Their substantial enzyme multiplicity may extend the range of environments in which normal development can take place and thereby may contribute to their apparent ecological success (T. miscellus is one of the most common weeds in and around Spokane, Washington).
Evolution © 1976 Society for the Study of Evolution