scholarly journals Reversals in complex traits uncovered as reticulation events: Lessons from the evolution of parity‐mode, chromosome morphology, and maternal resource transfer

Author(s):  
Jose L. Horreo ◽  
Teresa Suarez ◽  
Patrick S. Fitze
Author(s):  
Godfrey C. Hoskins

The first serious electron microscooic studies of chromosomes accompanied by pictures were by I. Elvers in 1941 and 1943. His prodigious study, from the manufacture of micronets to the development of procedures for interpreting electron micrographs has gone all but unnoticed. The application of todays sophisticated equipment confirms many of the findings he gleaned from interpretation of images distorted by the electron optics of that time. In his figure 18 he notes periodic arrangement of pepsin sensitive “prickles” now called secondary fibers. In his figure 66 precise regularity of arrangement of these fibers can be seen. In his figure 22 he reproduces Siegbahn's first stereoscopic electron micrograph of chromosomes.The two stereoscopic pairs of electron micrographs of a human chromosome presented here were taken with a metallurgical stage on a Phillips EM200. These views are interpreted as providing photographic evidence that primary fibers (1°F) about 1,200Å thick are surrounded by secondary fibers (2°F) arranged in regular intervals of about 2,800Å in this metanhase human chromosome. At the telomere the primary fibers bend back on themselves and entwine through the center of each of each chromatid. The secondary fibers are seen to continue to surround primary fibers at telomeres. Thus at telomeres, secondary fibers present a surface not unlike that of the side of the chromosome, and no more susceptible to the addition of broken elements from other chromosomes.


Author(s):  
R. V. Kulyan

The Russian Research Institute of Floriculture and Subtropical Crops has the citrus germplasm collection, in total over 150 genotypes of various origins including 30 wild and semi-wild relatives. As a result of controlled hybridization in 17 crossings combinations of with the participation of relatives of citrus plants, new 769 hybrid offspring were obtained, which combine the traits of both the maternal and paternal genotypes. Analyzing the populations, promising combinations were highlighted: C. reticulata × Fortunella margarita (47.1%); C. x natsudaidai × 3252 (42.1%) and C. reticulata × C. reticulata ‘Cleopatra’ (40.9%) to create the gene pool of distant hybrids. From the mentioned combinations of crossings the greatest percent of seedlings which phenotypes tend to cultivated varieties was received. This hybrid material is a valuable source for isolating forms that are resistant to extreme environmental factors. According to phenotypic characteristics, hybrids were divided into three categories: I – Cultural, II – Semi-wild and III – Wild. Of the first category, the largest number 87 prospective forms were selected, and can be of interest for further breeding. As a result of the study of interspecific hybrid seedlings, 137 promising forms have been identified, which are carriers the complex traits such as dwarfism, thornless, early maturity and increased winter hardiness. From this set 17 genotypes were selected, which received the status of an elite forms, which successfully pass the primary test, and will be also useful in further breeding work for creating sources with a complex of positive traits and on breeding new varieties of citrus crops resistant to growing conditions.


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