EXTRA, DIMINUTIVE CHROMOSOMES IN OENOTHERA

Mooring, John S. (Washington State U., Pullman.) A cytogenetic study of Clarkia unguiculata. II. Supernumerary chromosomes. Amer. Jour. Bot. 47(10): 847–854. Illus. 1960.—Supernumerary chromosomes morphologically comparable to those of the basic complement occur in high frequency in wild populations of this onagraceous annual plant. This paper evaluates the role that these supernumerary chromosomes play in the population dynamics of this species. The results of crossing plants with various numbers of supernumeraries showed that these chromosomes often increased in number in the seed parent. Examination of microsporocytes showed that almost 30% of the 491 plants determined had 1 or more supernumerary chromosomes. Studies of natural populations revealed that the frequency of individuals with supernumeraries varied from 0 to 79% in different populations, and also that in 1 population their frequency varied significantly in different years. It is concluded that supernumerary chromosomes in this species are adaptive under at least certain conditions. It is speculated that they are components of polygenic systems which increase tolerance to environmental extremes.

A Cytogenetic Study of Clarkia Unguiculata Ii. Supernumerary Chromosomes

Mooring

1960

Cytology of Supernumerary Chromosomes in Haplopappus Spinulosus Ssp. Cotula

Jackson

1961

Li, Ning, and R. C. Jackson. (U. Kansas, Lawrence.) Cytology of supernumerary chromosomes in Haplopappus spinulosus ssp. cotula. Amer. Jour. Bot. 48(5): 419–426. Illus. 1961.—The behavior of supernumerary chromosomes was investigated in 2 plants. In 1, the number of supernumeraries was highly variable in both somatic and meiotic cells, presumably as a result of somatic non‐disjunction. In the second plant, the number of supernumerary chromosomes was less variable, but an end‐to‐end association of a pair of supernumeraries and a regular bivalent was observed in a small percentage of the microsporocytes at zygotene and pachytene. This end‐to‐end association apparently resulted in a permanent fusion of the supernumerary and regular chromosome ends in some instances because the union persisted throughout both meiotic divisions. There was no evidence of normal pairing between the supernumeraries and regular chromosomes.

Evidence of Relationship Between Extra Diminutive Chromosomes in Geographically Remote Races of Oenothera

Cleland

Hyde

1963

Self Cite

CLELAND, R. E. (Indiana U., Bloomington), and B. B. HYDE. Evidence of relationship between extra diminutive chromosomes in geographically remote races of Oenothera. Amer. Jour. Bot. 50(2): 179-185. Illus. 1963.-Two California races of O. hookeri, Mono (from Mono Co.) and llfataguey (from San Diego Co.), have extra diminutive chromosomes. These diminutives do not associate with any of the normal chromosomes present. The extras from the 2 races, however, are able to synapse with each other and to form chiasmata, although the extras in Mono are distinctly larger than these in Mataguey. This suggests that they are at least partially homologous and that they have come from a common source. Two alternative hypotheses for their origin are suggested: (1) they have resulted from the loss of pairing ends through deletion, having descended from the same chromosome; (2) they represent normal chromosomes derived from another subgenus, through an inter-subgeneric cross followed by a backcross to hookeri. The facts tend to favor the latter hypothesis.