A Cytogenetic Study of Clarkia Unguiculata Ii. Supernumerary Chromosomes

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Analysis of 512 plants derived from 200 populations shows that the widely distributed western North American Chaenactis douglasii species‐complex consists of diploids (n = 6), triploids, tetraploids, and hexaploids. Microsporocytes were the source of most of the chromosome counts. About 9% of all plants examined had one or more full‐sized extra chromosomes. Multivalents, usually a ring or chain of four chromosomes, were almost entirely restricted to polyploids, where one or more were identified in 38% of the tetraploids and 33% of the hexaploids. With two exceptions, diploids and polyploids were not found in the same population. Frequencies of diploid, triploid, tetraploid, and hexaploid populations were, respectively, 34, 1.5, 55 and 9.5%. With significant exceptions, diploid populations predominate in the Pacific and Rocky Mountain Systems, whereas polyploid ones are most frequent in the intervening plateaus. Ploidy level is correlated with age of substrate, rather than with climate, elevation, vegetation, or soil type. Range, morphology, ploidy level, and meiotic behavior suggest that var. achilleifolia tetraploids and hexaploids are descendents of hybrids between other variants of the complex. The diploid‐tetraploid‐hexaploid geographic distribution and the age of the substrates where each tends to occur suggest that the complex evolved in late Cenozoic time in response to major climatic and geologic changes that induced migration and hybridization. The hybrid derivatives, stabilized by polyploidy and tolerant of increasing aridity, came to occupy newly available habitats in areas disturbed by volcanic activity and glacial or glacial‐related processes.

Section: Discussion-extra Chromosomes-that Individuals With Extra Chrmentioning

confidence: 95%

mentioning

confidence: 99%

A Cytogeographic Study of Chaenactis Douglasii (Compositae, Helenieae)

Mooring

1980

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Trisomic Transmission in Clarkia Unguiculata

Vasek

1961

Vasek, F. C. (U. California, Riverside.) Trisomic transmission in Clarkia unguiculata. Amer. Jour. Bot. 48(9): 829–833. 1961.—Seven primary trisomic plants derived from a triploid‐diploid cross were self‐pollinated. The 7 progenies included diploids and trisomics, the latter varying in frequency from 16 to 30%. In addition, 2 of the progenies included tetrasomic plants. Crosses were made between diploids and either trisomics or tetrasomics. The extra chromosome of 1 progeny was readily transmitted through the pollen of trisomic and tetrasomic plants. When a trisomic of the same progeny was used as a seed parent, only diploids and tetrasomics were found among the offspring, indicating a duplication of the extra chromosome. The extra chromosomes of other progenies were not transmitted through either pollen or eggs in controlled diploid‐trisomic crosses but trisomics of these progenies were recovered after self‐pollination. It is suggested that differential pollen‐tube growth precluded transmission to diploid‐trisomic hybrids and that under conditions of reduced pollen competition the extra chromosome normally would be transmitted through pollen. The extra chromosomes generally occur as univalents at metaphase and are ordinarily included in telophase nuclei.

Cytogenetic Studies in Clarkia, Section Primigenia. I. A Cytological Survey of Clarkia Amoena

Abdel-Hameed

Snow

1963

Snow, Richard. (U. California, Davis.) Cytogenetic studies in Clarkia, section Primigenia. I. A cytological survey of Clarkia amoena. Amer. Jour. Bot. 50(4): 337–348. Illus. 1963.—Clarkia amoena (2n = 14) shows great cytological diversity based on reciprocal translocations. About ½ the plants sampled were heterozygotes; in 2 of the subspecies the frequency was as high as ⅔. The metaphase configurations were varied, including rings of 4, 6, 8, 4 + 4, 6 + 4, and more unusual types forming a chain of 3 + a univalent or a chain of 4 + a univalent. The latter have only 13 chromosomes but are not true monosomies. Some plants with supernumerary chromosomes were found, in addition to a plant with only 12 chromosomes which was derived from a “monosomic” type. From crosses of various homozygous lines to a standard strain, it was found that the standard end arrangement of chromosomes occurs widely and commonly throughout the species. A minimum of 7 different end arrangements, giving a ring of 4 with the standard strain, and 1 giving a ring of 6, account for the chromosome pairing found in interstrain crosses. No doubt more would be found with further testing. Some of the translocations may be components of adaptive polymorphic systems, though there is no proof of this yet. No balanced lethal systems similar to those in the closely related genus Oenothera were found.