The estimation of parental genotypes by the analysis of a fixed number of their offspring

When genotypes are cryptic in adult organisms but visible in young life-stages, it is possible to estimate the genotypes in parents after the examination of a fixed number of their offspring. Thus, in Drosophila, males collected in the wild can be crossed to females of a homozygous laboratory stock, and the identification for genotype of seven larvae is largely enough to guarantee a correct diagnosis of the two alleles of the father (P = 0.984). On the other hand, when collected females were inseminated in nature, it should be possible to determine the constitution both the female and her mate, after the analysis of a sufficient number of their offspring. Nevertheless, exact formulas for the probabilities of correct diagnoses of parental genotypes in this case have not yet been published. In this paper we derive such formulas, and illustrate their application. The conclusion we draw from our calculations is that, unless 13 larvae are examined among the offspring, the probability of misdiagnosis is over the 0.05 level. Of course, the errors produced become greater as smaller offspring numbers are analyzed. But in the case of one locus with two alleles, we have derived formulas to correct the observed number of matings and estimate its actual number in the sample, for any offspring sample size. After these corrections, we have been able to calculate estimates of relative mating frequencies in the sampled population, together with their associated errors, which can be subsequently used in studies of adult fitness components, mainly in those dealing with sexual selection.     

The Evolutionary History of DROSOPHILA BUZZATII. Xii. the Genetic Basis of Sterility in Hybrids between D. BUZZATII and Its Sibling D. SERIDO from Argentina

The genetic basis of hybrid sterility has been investigated in backcross segmental hybrids between two sibling species, Drosophila buzzatii and D. serido. Asynapsis of homologous bands in hybrid polytene chromosomes has been used to identify the D. serido chromosome segments introgressed into the D. buzzatti genome. All the investigated chromosomes contain male sterility factors. For autosomes, sterility is produced when an introgressed D. serido chromosome segment, or combination of segments, reaches a minimum size. On the other hand, any introgressed X chromosome segment from D. serido, irrespective of its size, produces either male hybrid sterility or inviability.     

Spermiogenesis of inversion heterozygotes in backcross hybrids between Drosophila buzzatii and D. serido

Interspecific F1 hybrid females of D. serido and D. buzzatii are fertile, but hybrid males are sterile. By successive backcrossing of hybrid females to D. buzzatii males it is possible to diminish the genomic contribution of D. serido to the hybrid karyotype. Finally, only selected chromosome sections of D. serido known as inversions restricted to this species were individually left in the otherwise D. buzzatii karyotype, namely: 2 C2b-F4a (j⁹m⁹n⁹), 2 B2c-F4a (j⁹k⁹), 3 C5a-G1b (k²), 4 E2a-G2f (m) and 5 C5d-F2h (w). The present paper deals with the influence of these chromosome sections on sperm differentiation. Any of them produces hybrid male sterility in heterozygous condition. We analyzed spermiogenesis using the DNA specific fluorescence dye BAO in hybrid males which were heterozygous either for only one inversion, as in chromosomes 3, 4 and 5, or for a series of inversions on the same chromosome, as in chromosome 2. The abnormalities recorded included abnormal formation of the cysts, lower than normal number of cysts, abnormal number of nuclei per cyst, incomplete elongation of the cyst, incomplete elongation of the nuclei, displacement of the nuclei from the head region of the cyst and lack of individualization. In no case was there any contents in the seminal vesicle. The section from chromosome 2 of D. serido had the most drastic effect; the disruption produced by the chromosome section corresponding to inversion 3 k² was only a little more severe than that due to 5 w, and both may be distinguished only quantitatively; inversion 4 m produced the slightest deviation from normal spermiogenesis. The larger the serido section introduced in the hybrid, the more severe were the abnormalities it produced. An interpretation in terms of a balance genic theory on the functioning of the genetic system is given.This is paper No. VII in the series The evolutionary history of Drosophila buzzatii.     

Growth of Odontesthes bonariiensis (Atherinidae) larvae feeding on suboptimal zooplankton densities

Synopsis In this study we investigate the effect of food availability (zooplankton biomass) on the growth of Odontesthes bonariensis (Atherinidae) larvae. The larvae were stocked in four 45 m² outdoor tanks at relatively high densities (100 and 200 larvae m^–2). Because of the high stocking densities, the zooplankton biomass was depleted in all tanks. However, the patterns of food limitation, and particularly periods of severe food shortage, differed in tanks stocked at different densities. We could therefore, observe the effect of food limitation in larvae that differed in weight and age. The effects of variables suspected to influence O. bonariensis growth rates (age and weight of larvae, available zooplankton biomass, mean individual weight of available preys, total ingested prey weight, and mean weight of ingested preys) were investigated using standard multiple regression methods, and a model assuming: (1) an allometric relationship between maximum growth rates and weight of larvae, and (2) an inverse relationship between growth depression and the available zooplankton biomass. Both methods were consistent in showing that only the weight of larvae, and the availability of zooplankton prey had significant effects on the growth of O. bonariensis. The model's results additionally suggest that, if the observed growth rates are scaled by the maximum growth rate corresponding to the larva weight, the effect of zooplankton biomass is largely independent of age and weight of larvae.     

Fine mapping of the Autosomal Dominant Split Hand/Split Foot Locus on Chromosome 7, Band q21.3-q22.1

Split hand/split foot (SHFD) is a human developmental defect characterized by missing digits, fusion of remaining digits, and a deep median cleft in the hands and feet. Cytogenetic studies of deletions and translocations associated with this disorder have indicated that an autosomal dominant split hand/split foot locus (gene SHFD1) maps to 7q21-q22. To characterize the SHFD1 locus, somatic cell hybrid lines were constructed from cytogenetically abnormal individuals with SHFD. Molecular analysis resulted in the localization of 93 DNA markers to one of 10 intervals surrounding the SHFD1 locus. The translocation breakpoints in four SHFD patients were encompassed by the smallest region of overlap among the SHFD-associated deletions. The order of DNA markers in the SHFD1 critical region has been defined as PON–D7S812–SHFD1–D7S811–ASNS. One DNA marker, D7S811, detected altered restriction enzyme fragments in three patients with translocations when examined by pulsed-field gel electro-phoresis (PFGE). These data map SHFD1, a gene that is crucial for human limb differentiation, to a small interval in the q21.3-q22.1 region of human chromosome 7.     

Probability of mast cells to mediate anaphylaxis in skeletal muscle

Are there enough mast cells in denervated skeletal muscle to account for autopharmacological mediation of the antigen potentials (APs) elicited by microtaps? Through rough qualitative estimations, some authors have suggested a positive answer to this question. However, in view of measurements performed in this investigation of both the density of mast cells and the diffusion coefficient of antigens, the probability of such mediated effects was found to be relatively low:P=0.016 for egg albumin andP=0.004 for ferritin. Therefore, most APs induced by microtaps should be attributed to the direct effect of antigen over the sensitized muscle fibers. Yet, both the density of mast cells found in this work and the known amount of histamine they are capable of releasing when challenged with antigen, support the hypothesis regarding the involvement of these cells when antigen is massively superfused so as to induce Schultz-Dale reactions in muscle strips. Under this circumstance, the direct and mediated mechanisms may coexist.     

Root/Shoot Allocation and Root Architecture in Seedlings: Variation among Forest Sites, Microhabitats, and Ecological Groups1

I analyzed patterns of variation in root mass allocation and root morphology among seedlings of woody species in relation to environmental factors in four Neotropical forests. Among forests, I explored the response of root traits to sites varying in water or nutrient availability. Within each forest, I explored the plastic response of species to different microhabitats: gaps and understory. Additionally, I explored evidence for life history correlation of root and shoot traits by comparing species differing in their successional group (light‐demanding [22 spp.] or shade tolerant [27 spp.]) and germination type (species with photosynthetic cotyledons or species with reserve cotyledons). At each forest site, young seedlings from 10 to 20 species were excavated. A total of 55 species was collected in understory conditions and 31 of them were also collected in gaps. From each seedling, six morphological ratios were determined. Allocation to roots was higher in forest sites with the lowest soil resources. Roots were finer and longer in the most infertile site, while roots were deeper in the site with the longest dry season. Seedling traits did not differ between germination types. Shade tolerant species allocated more to roots and developed thicker roots than light‐demanding species. Light‐demanding species showed stronger plastic responses to habitat than shade tolerant species, and species with photo‐synthetic cotyledons showed lower plasticity than species with reserve cotyledons. Overall, these results suggest that among Neotropical species, root allocation and root morphology of seedlings reflect plant adjustments to water or nutrient availability at geographic and microhabitat scales. In addition, life history specialization to light environments is suggested by differences among groups of species in their allocation to roots and in their root morphology.     

Mutational analysis of the RecA protein L1 region identifies this area as a probable part of the co-protease substrate binding site

Previous mutational analysis of the L1 region of the RecA protein suggested that Gly-157 and Glu-158 are 'hot-spots' for the occurrence of constitutive LexA co-protease mutants (coprt^c). In the present study, we clearly establish that position 157 is a hot-spot for the occurrence of such mutants, as 12 of 14 and 10 of 14 substitutions result in this phenotype for UmuD and LexA cleavage respectively. The frequency of such mutations at position 158 is somewhat lower, 8 of 13 and 5 of 13 for UmuD and LexA respectively. Comparison of the UmuD vs. LexA co-protease activity for all single mutants with substitutions at positions 154, 155, 156, 157 and 158 (47 in total) reveals that, although there is good agreement among most mutants regarding their ability to cleave both LexA and UmuD, there are two in particular (Glu-154→Asp and Glu-154→Gln) that show a clear preference for cleavage of UmuD. We also show that three second-site mutations that completely suppress coprt^c activity toward LexA have little or no effect on the coprt^c activity of the primary mutant toward UmuD. In addition, we observe a high frequency of second-site suppressor mutations, suggesting a functional interaction among side-chains in this region. Together, these results support the idea that the L1 region of RecA makes up part of the co-protease substrate-binding site.