Genes conferring fertility restoration, in each of the following three hexaploid restorer lines of common wheat (Triticum aestivum L) carrying cytoplasm of Triticum timopheevi Zhuk, were located using monosomic analyses: [(T. timopheevi × Aegilops squarrosa) × Canthatch3] F7, [(T. timopheevi × Ae. squarrosa) × Dirk3] F6 and (T. timopheevi × Ae. squarrosa) × Karn3] F6.Testcross data revealed that in the Dirk restorer, a major gene (Rf1) conferring fertility restoration was carried on chromosome 1A, while a minor gene (Rf4) was located on chromosome 7D. The restorer line of Canthatch was found to carry a major gene (Rf2) and a minor gene (Rf3) on chromosomes 6B ad 6D respectively. Chromosomes 1A and 6B were found to carry genes for fertility restoration in the Karn restorer. Critical chromosomes carrying genes conferring fertility restoration in each of the three restorer lines were found not to be involved in translocations found in F1 plants of Rescue monosomics × restorer lines. Chromosomes 2A, 6A and 3D of Rescue appeared to carry genes which modified the degree of restoration obtained.
To ascertain whether the genotypic similarity of monozygotic twin partners is reflected in their chromosome measurements despite the crudeness of presently available techniques, the lengths of the long and short arms were measured in 10 cells (5 from each twin partner) from 10 pairs (3 male and 7 female) of aged monozygotic twins. In total, then, measurements were available from 100 cells, derived from peripheral leukocyte cultures of subjects ranging in age between 78 and 89 years. Measurements were made by hand, rather than computer, from photographic karyotypes as customarily constructed in cytogenetic laboratories. The centromeric index, rather than the arm ratio, proved mathematically to be the more precise measure of the relative position of the centromere and, supporting the recommendation of others, it is urged that it be the only measure used. Of the two parameters measuring relative total length, the one relative to the autosomal sum seems preferable to the one relative to the autosomal sum plus X on other than statistical grounds. Even though the present measurements were derived from aged twins, they are in general agreement with those reported in the literature for younger single borns and, like those of other investigators, show marked intraindividual variability combined with relatively low variability between persons. Nonetheless, there emerges for relative length, the seemingly more accurate of the two measures, the indication of greater homogeneity within pairs of monozygotic twins than between pairs. Larger samples, including younger age groups and dizygotic pairs, with many more cells per individual need to be studied before definitive conclusions can be drawn.
This first longitudinal study on aged subjects confirms previous cross-sectional observations of increasing aneuploidy with advancing age in women but not in men. In this study of 17 aged twins (mean age 89.7 years), 11 women and 6 men, spanning an interval of approximately 6 years between examinations, only women showed a significant increase in hypodiploidy (also hyperdiploidy and monosomy C). This increase in hypodiploidy was not due to a high frequency of chromosome loss in a few subjects but rather was exhibited by most of the subjects. While men showed a loss in G-group chromosomes during this 6-year interval, that loss was not statistically significant. These findings confirm for the first time by means of longitudinal follow-up that women and not men, even in the ninth decade of life, show a significant increase in hypodiploidy.
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