Cytogenetics of the acrotrisomic 5S5L in barley

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.

Genetic and demographic effects of single wild-type immigrants on a mutant population of Tribolium castaneum

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.

The expected probabilities of identity for the circular stepping-stone model

The expected values of the probabilities of identity by descent are derived for the circular stepping-stone model. The results are more easily interpreted than those derived previously.Key words: model, population, ecology.

Spontaneous mutability and colony morphology of Gibberella baccata

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.

Identification of mRNAs encoding low molecular mass heat-shock proteins in maize (Zea mays L.)

Subjecting 5-day-old maize seedlings to a rapid elevation in growth temperature (heat shock; 25–42 °C) results in a shift in the pattern of protein synthesis in maize plumules from the production of a broad spectrum of proteins to the new and (or) enhanced synthesis of a small number of heat-shock proteins (HSPs). The low relative molecular mass (Mr) HSPs, and more specifically an 18-kDa HSP with four major isoelectric variants, represent the majority of HSP synthesis following cell-free translation of total cellular poly (A)+ RNAs and polyribosomal RNAs extracted from heat-shocked plumules. Immunochemical studies, using polyclonal antibodies raised against the 18-kDa HSPs, show that the 18-kDa HSPs synthesized in vitro share immunochemical properties with HSPs of the same Mr synthesized in vivo by heat-shocked plumules. Furthermore, size fractionation and translation analyses of total cellular poly(A)+ RNAs extracted from heat-shocked plumules demonstrate that poly(A)+ RNAs encoding an 18-kDa HSP(s) have an estimated size of 0.6–0.95 kilobases. The observation that 18-kDa HSPs are absent among the translation products and immunoprecipitates of proteins synthesized in vitro by RNAs extracted from control plumules (25 °C) suggests that the mRNAs encoding 18-kDa HSPs are heat-shock induced.Key words: mRNA, maize, heat shock.

Random environmental variation and inbreeding: effects on pure-strain and hybrid populations of flour beetles (Tribolium)

The effect of inbreeding and of random environmental variation on fitness characters was studied in small populations derived from 10 inbred laboratory strains of Tribolium castaneum (I) and in 18 hybrids (IH) populations, obtained by crossing six mutant to three wild-type strains. Replicate population of each type were held in a constant (C) and a randomly varying (V) environment. Each replicate population was founded by a single pair of adults and one pair of sibs founded each subsequent generation. Thus four groups of inbreeding populations were created: IC, IV, IHC, and IHV. Outbred hybrid populations were held in the varying environment (OV). Several fitness characters were measured. The results confirmed that inbreeding populations exposed to random environmental variation had lower fitness than similar populations in the constant environment populations, as expected (IHC > IHV, IC > IV for each fitness trait). The environmental stress did not result in selection for individuals with higher fitness. In the hybrid populations, consistent and significant differences in fitness between populations having different wild-type (female) ancestors persisted for several generations. No such differences were found among populations grouped by their mutant ancestor. Within each environment, inbreeding had a pronounced effect on fitness. The order of magnitude of the fitness characters was IHC > IC, OV > IHV > IV, parallel to the level of inbreeding. Directional changes in relative (rank) magnitude of fitness characters among populations suggested that their genetic composition was changing temporally.Key words: Tribolium, selection, fitness, inbreedig, population.

Temperature-stress response in maize: a comparison of several cultivars

The protein synthetic response to a heat (28–41 °C) and a cold (28–4 °C) shock was studied in seedlings from 10 cultivars of maize with varying levels of cold tolerance. This response was compared by fluorography of one-dimensional polyacrylamide gels and immunoblot analysis. We utilized polyclonal antibodies against the 18 000 dalton (Da) heat-shock protein and the 73 000–89 000 Da heat-shock protein complex from Oh43 maize seedlings to ascertain antigenic similarity of these polypeptides. The heat-shock response varied in the numbers and relative molecular masses of the heat-shock proteins. Only three polypeptides appeared to be conserved across cultivars: a 93 000, 71 000, and 18 000 Da polypeptide. The cold-shock response varied from none to a dramatically altered pattern in a few cultivars. Thus, the heat- and cold-shock responses in these cultivars of corn differ in the types of polypeptides that are induced. All cultivars showed varying degrees of cross-reactivity when probed with the anti 18 000 Da heat-shock protein antibody. The inbred lines appeared to respond more to a cold shock than the hybrid lines but there was little relationship between the cold tolerance and the induction of a cold-shock response. Two of the cultivars demonstrated unique binding to a higher molecular weight polypeptide under control (28 °C) conditions. These data suggest that within species variation in both number and relative molecular weight of thermal stress polypeptides (heat and cold) is a function of genotype.Key words: heat shock, cold shock, cold tolerance, maize, gene expression.

Differentiation of H genomes in the genus Critesion: evidence from synthetic hybrids involving Elymus and Critesion and one natural hybrid of C. violaceum and C. bogdanii

Hybrids of Elymus canadensis (2n = 28; SSHH) × Critesion californicum (2n = 14) and E. canadensis × C. bulbosum (2n = 14) were synthesized at relative frequencies of 11.8 and 0.3%, respectively, by the aid of embryo rescue techniques. A natural hybrid was identified as C. violaceum × C. bogdanii (2n = 14) by a combination of karytotype analysis and plant morphology. Gross spike morphology of the hybrids was intermediate to that of the parents. Meiotic chromosome pairings in these hybrids suggested that the genome of C. californicum and C. bogdanii is more or less homologous with one of the two genomes of E. canadensis. Genomes of C. violaceum and C. bulbosum appeared to be different from each other and from those in C. bogdanii and C. californicum. Based on the data in this study and others, the degree of genome differentiation among some Critesion and some Elymus species containing the H genome was examined and discussed. The symbol H is proposed for the genome in C. bogdanii and C. californicum, Hv for C. violaceum, Hb for C. bulbosum, and Hc for C. chilense.Key words: interspecific hybrids, synapsis, phylogeny, Hordeum, Elymus, Critesion.

Use of Neurospora Spore killer strains to obtain centromere linkage data without dissecting asci

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.