Canadian Journal of Genetics and Cytology

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ISSN : 0008-4093
Published by: Canadian Science Publishing (10.1139)
Total articles ≅ 2,587
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Geoffrey K. Rickards
Canadian Journal of Genetics and Cytology, Volume 28, pp 926-931; https://doi.org/10.1139/g86-129

Abstract:
Genetically balanced and unbalanced microspores of an interchange heterozygote of Allium triquetrum are shown to behave differently with respect to their first pollen grain mitosis (PGMI). Two types of unbalanced microspores abort immediately prior to PGMI, while another two types are delayed in their progression through PGMI. The data presented have relevance to transmission potentials of unbalanced postmeiotic cells and estimates of their frequencies in interchange (reciprocal translocation) heterozygotes.Key words: differential behaviour, unbalanced cells, pollen grain mitosis, interchange heterozygosity.
E. B. Lawrence, Paul E. Nelson, T. A. Toussoun
Canadian Journal of Genetics and Cytology, Volume 28, pp 932-941; https://doi.org/10.1139/g86-130

Abstract:
Cultural instability is a common phenomenon in the genus Fusarium. As with other species, Gibberella baccata (Fusarium lateritium) contains cultures that are less morphologically stable than others. When grown on certain media, such as potato dextrose agar, these cultures produce areas of aberrant growth (mutant patches) after 6 weeks. Single conidial cultures from these patches produce colonies different from the original culture and from each other in growth rate, colony color, aerial mycelium production, and pionnote production. Random ascospore analyses of crosses of the original morphological type to the mutant types showed there had been a one gene change in each case. Mutant patch forming and nonforming isolates of Gibberella baccata were crossed in all possible combinations, and the progeny were rated for ability to produce mutant patches. Broad sense heritability estimates for inheritance of mutant patch formation were high (60.0 to 95.9%), strongly indicating a genetic basis with a limited number of genes involved. The mutator activity of these genes appeared to be conditional and mutant patch development was dependent on the presence of some unknown factor in certain media rich in carbohydrates and other compounds.Key words: Gibberella baccata, Fusarium lateritium, colony morphology, spontaneous mutability, cultural instability.
, Raymond P. Guries
Canadian Journal of Genetics and Cytology, Volume 28, pp 942-946; https://doi.org/10.1139/g86-131

Abstract:
Lethal genetic load might be caused by a few lethal genes or by large numbers of mildly deleterious polygenes. The extent of this lethal load can be quantified as the number of "lethal equivalents" in each individual. If there are large numbers of deleterious genes scattered throughout the genome then we might expect a correlation between the number of lethal equivalents and the level of heterozygosity at isozyme marker loci. Using data from 52 isozyme loci, we estimated this correlation on 68 individuals in four conifer species (Pinus ponderosa Laws., Pinus contorta Dougl., Picea glauca (Moench) Voss., and Pseudotsuga menziesii (Mirb.) Franco). No significant correlation was detected. We interpret this consistent result in four species as indicating that lethal equivalents do not represent large numbers of mildly deleterious polygenes in these forest trees.Key words: genetic load, lethal equivalent, Pinaceae, heterozygosity.
B. E. Ballachey, W. D. Hohenboken, D. P. Evenson
Canadian Journal of Genetics and Cytology, Volume 28, pp 954-966; https://doi.org/10.1139/g86-133

Abstract:
Genetic factors affecting spermatogenesis, sperm morphology, and chromatin structure in mice were estimated using a diallel cross of the inbred lines C3H/HeJ, C57BL/6J, DBA/2J, and BALB/cByJ. Flow cytometry of acridine orange stained cells was used to evaluate (i) proportions of testicular tetraploid, diploid, and haploid cells and (ii) nuclear chromatin structure of sperm, measured by resistance of chromatin to in situ acid denaturation, and quantified by the ratio of double- to single-stranded DNA (αt). Percent morphologically abnormal sperm was scored by light microscopy. Heterosis, line, maternal, and reciprocal effects, and general and specific combining abilities were estimated for body and testis weights, testicular cell proportions, sperm αt values, and percent abnormal sperm. Heterosis was important for testis weight, αt values, and percent abnormal sperm. Inbreds varied in body and testicular weights, αt values, and percent abormal sperm. Significant maternal effects were noted for several traits but could be due to sex-linked (X or Y) factors, since maternal and sex-linked effects were confounded. Although a high positive correlation existed between αt values and percent abnormal sperm, the proportion of sperm with altered chromatin structure, measured by FCM, was generally much lower than proportion of morphologically abnormal cells.Key words: mouse, spermatogenesis, chromatin structure, flow cytometry, diallel.
David D. Perkins, Namboori B. Raju, Virginia C. Pollard, Joseph L. Campbell, Adam M. Richman
Canadian Journal of Genetics and Cytology, Volume 28, pp 971-981; https://doi.org/10.1139/g86-135

Abstract:
Use of a centromere-linked Spore killer gene Sk reduces manyfold the labor involved in obtaining tetrad data that would otherwise require ordered dissection of intact linear eight-spored asci. Heterozygous crosses are made for Spore killer (SkK × SkS) and for markers to be tested. In such crosses only SkK ascospores survive. The four viable (SkK) and four aborted (SkS) ascospores of each ascus are ejected from the perithecium as a physically disordered group. The four surviving SkK ascospores of individual asci are germinated and scored. SkK segregates from SkS at the first meiotic division. If both marker alleles are represented in the surviving products, they must therefore have segregated from one another at the second division. Four-spore (Fsp) genes have been used to eliminate one postmeiotic nuclear division, so that only two ascospores per ascus need to be scored. The Spore killer method has been useful for mapping closely linked genes in centromere regions, for identifying genes that are far out on chromosome arms, for obtaining information on meiotic crossing-over, and for comparing linkages in different species.Key words: tetrad analysis, centromere mapping, Spore killer, Neurospora.
Namboori B. Raju
Canadian Journal of Genetics and Cytology, Volume 28, pp 982-990; https://doi.org/10.1139/g86-136

Abstract:
Two nonallelic Four-spore mutants are known in which ascospore walls enclose the four immediate products of meiosis rather than the normal eight products of a postmeiotic mitosis. Expression depends on temperature. The Four-spore phenotype is expressed when the developing asci are subjected either to high temperatures (25–30 °C) for Fsp-1 or to low temperatures (15–20 °C) for Fsp-2. Heterozygous Fsp-1 × Fsp-1+ crosses make eight-spored asci at 15–20 °C but produce many four-spored asci at 25 °C and mostly four-spored asci at 30 °C. Homozygous Fsp-1 × Fsp-1 crosses respond similarly to increasing temperature but make 40–50% four-spored asci even at 20 °C. Heterozygous Fsp-2 × Fsp-2+ crosses produce almost exclusively four-spored asci at 15 °C but a mixture of four- and eight-spored asci at 20, 25, and 30 °C. Homozygous Fsp-2 × Fsp-2 crosses make all four-spored asci at 15 and 20 °C and a mixture of four- and eight-spored asci at 25 and 30 °C. When both Fsp-1 and Fsp-2 are present in a cross, either homozygous or heterozygous, no asci contain more than four ascospores at any temperature. Limited temperature-shift experiments with Fsp-1 and Fsp-2 show that the sensitive period for Four-spore expression is sometime after meiotic prophase, possibly at interphase II.Key words: Neurospora, temperature sensitive, Four-spore mutants, large ascospores.
D. W. A. Roberts
Canadian Journal of Genetics and Cytology, Volume 28, pp 991-997; https://doi.org/10.1139/g86-137

Abstract:
'Rescue', 'Cadet', and the 42 reciprocal chromosome substitution lines derived from these two spring wheat cultivars were tested for vernalization response and cold hardiness. Cold hardiness was tested after hardening under a 16-h day for 8 weeks with 6 °C day and 4 °C night temperatures or in the dark for 7 weeks at 0.8 °C followed by 8 weeks at −5 °C. Chromosomes 5A, 5B, 7B, and possibly 2A carried loci for vernalization response. Chromosomes 2A, 5A, and 5B carried loci affecting cold hardiness measured after 8 weeks in the light at 6 °C during the day and 4 °C at night, whereas chromosomes 6A, 3B, 5B, and 5D were involved in cold hardiness after hardening in the dark at 0.8 °C followed by −5 °C. The results suggest that the rank order of cultivars for cold hardiness depends on the hardening technique used since the two different techniques tested had different genetic and presumably somewhat different biochemical bases.Key words: Triticum aestivum L., cold hardiness, vernalization.
Ram S. Verma, Jorge Rodriguez, Arvind Babu, Sundari Chemitiganti, Morton Coleman, Richard T. Silver, Harvey Dosik
Canadian Journal of Genetics and Cytology, Volume 28, pp 998-1002; https://doi.org/10.1139/g86-138

Abstract:
The secondary constriction region (h) of human chromosome 9 was evaluated in 55 chronic myelogenous leukemia (CML) patients with respect to its size and position. Each case was examined by C-banding and distamycin A–4,6-diamidino-2-phenylindole techniques for the expression of the h regions. When one h region of chromosome 9 was larger, it was more frequently involved in the reciprocal translocation with chromosome 22. In addition, there was a higher incidence of pericentric inversions in the h regions in the translocated chromosome 9 when compared with normal homologues. The role of the constitutive heterochromatin of chromosome 9 as a possible influencing factor during 9q;22q translocation in CML is suggested.Key words: chromosomes 9 and 22, leukemia C-banding, DA–DAPI technique, heterochromatin.
Michael A. Delgado, Duwayne C. Englert
Canadian Journal of Genetics and Cytology, Volume 28, pp 1003-1008; https://doi.org/10.1139/g86-139

Abstract:
The effects of single wild-type immigrants on populations of Tribolium castaneum initially homozygous for the antennapedia (ap) allele were examined in reference to gene frequencies and age structures. One population received a wild-type male, another received a wild-type female, and the control population received no wild-type immigrant. The rate of increase in the wild-type gene frequency was significantly higher in the female immigrant population. Rapid increase in heterozygosity for this population resulted in a higher average number of adults than for the other two treatment groups. No significant differences in the numbers of larvae and pupae were observed. Results indicated increased larval survivability to be the major factor in establishment of the wild-type gene and the sex of the immigrant in the rate of increase.Key words: Tribolium, population, selection, immigration, antennapedia.
A. Shahla, T. Tsuchiya
Canadian Journal of Genetics and Cytology, Volume 28, pp 1026-1033; https://doi.org/10.1139/g86-143

Abstract:
An acrotrisomic plant was identified in the progeny of a telotrisomic for 1S. The acrocentric chromosome had a complete short arm (5S) and 40% of the proximal segment of the long arm (5L). Morphology of the acrotrisomic 5S5L was similar to the primary trisomic (triplo 5) and triplo 5L. At meiosis the acrocentric 5S5L either paired with its normal homologues forming a trivalent or remained as a univalent. Seed fertility was high. Transmission of the acrocentric was 37.6% through the female and 9% through the male. Genetic tests showed that fs2 and g were located in this 40% proximal segment of the 5L. Gene f3 showed a trisomic ratio with acrotrisomic 5S5L, but its arm location is not known. Two genes, f7 and trd, were located on the 60% distal segment of the 5L. The segregation ratio with gene int-a1 was also disomic but it could not be assigned to the 60% distal segment because its location on chromosome 5 is questionable at this time. This experiment demonstrates the usefulness of acrotrisomics in physical gene mapping by locating genes on a specific segment of the chromosome arm.Key words: acrotrisomic, barley, acrocentric, trisomic, telotrisomic.
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