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M A Toro

Publications and source records attributed to M A Toro.

12 recordsLinked to original sources
PubMed1999

Robust QTL effect estimation using the minimum distance method.

Robustness has received little attention in QTL studies. We compare Maximum Likelihood (ML) and the Minimum Distance (MD) methods when there exists data contamination caused by outliers. A backcross population of size (N) 200 and 500 and 0, 5 or 25 outliers was simulated. The mean and standard deviation of the first QTL genotype were set to 1. Four cases were considered: (i) micro2=1, sigma2=1; (ii)micro2=1, sigma2=1.25; (iii) micro2=1.252, sigma2=1; (iv) micro2=1.282, sigma2=1.25, where micro2 and sigma2 are the mean and standard deviation of the second genotype. Either full or selective genotyping was considered. A Monte Carlo MD method is proposed to deal with missing genotypes. MD estimates were much more robust than ML estimates, especially with respect to scale parameter estimates, and with selective genotyping.

Genotype↗
PubMed1999

Improving the efficiency of artificial selection: more selection pressure with less inbreeding.

The use of population genetic variability in present-day selection schemes can be improved to reduce inbreeding rate and inbreeding depression without impairing genetic progress. We performed an experiment with Drosophila melanogaster to test mate selection, an optimizing method that uses linear programming to maximize the selection differential applied while at the same time respecting a restriction on the increase in inbreeding expected in the next generation. Previous studies about mate selection used computer simulation on simple additive genetic models, and no experiment with a real character in a real population had been carried out. After six selection generations, the optimized lines showed an increase in cumulated phenotypic selection differential of 10.76%, and at the same time, a reduction of 19.91 and 60.47% in inbreeding coefficient mean and variance, respectively. The increased selection pressure would bring greater selection response, and in fact, the observed change in the selected trait was on average 31.03% greater in the optimized lines. These improvements in the selection scheme were not made at the expense of the long-term expectations of genetic variability in the population, as these expectations were very similar for both mate selection and conventionally selected lines in our experiment.

Animals↗
PubMed1998

Spontaneous mutation for life-history traits in Drosophila melanogaster.

Spontaneous mutations accumulated during 80 generations in 94 lines derived from a completely homozygous population of Drosophila melanogaster, all of them maintained by a single brother-sister mating per generation. Three traits were evaluated: early productivity, late productivity, and longevity. Mutational heritabilities were similar for all traits: 3.18 x 10(-3), 3.52 x 10(-3), and 3.38 x 10(-3), respectively. Nine lines were examined, their means being in the upper or lower tails of the distribution of line's means for at least two traits. Reciprocal crosses were made between each line and the control population to estimate line effects. The results can be summarised as follows: all lines carried putative mutations affecting fitness traits; five lines affect the three traits scored; one affects exclusively early productivity; and three affect exclusively late life-history traits (late productivity and longevity). Most mutations were deleterious and recessive, except one that favourably affected early-productivity and was dominant. Additional fitness traits were evaluated, indicating pleiotropy. We have not found mutations with antagonistic effects early and late in life; moreover, positive mutational correlation seems to be the rule.

Animals↗
PubMed1998

[Lipoxygenase and trypsin inhibitor inactivation in soymilk processing by direct milling and ultra high temperature (DM-UHT)].

Soymilk production by a new process based on Direct Milling of soy grits and Ultra High Temperature (DM-UHT) has been studied at laboratory scale in order to evaluate solids and protein extraction, lipoxygenases (LO) and Trypsin Inhibitors (TI) inactivation during milling and heat-treatment steps. For TI measurements in soy extracts and soymilk a modification of the classical Kakade method (17) was used. Highest extraction yields were accomplished at 70 degrees C and 2 minutes milling of soy grits. LO was appreciably inactivated when using, as dispersing medium for milling, 0.01M sodium carbonate (Residual Activity 14%) instead of water (Residual Activity 46%), so in this way lower levels of undesired substances can be generated. LO destruction in the resulting suspension was finished by a short heating (30 seconds) from 70 degrees C to boiling temperature (96 degrees C). On the other hand, TI were not fully inactivated in milling nor even in the steaming step at 96 degrees C for many minutes. The TI were inactivated to the accepted levels for soymilk in the final UHT step at 135 degrees C and 2 minutes, being possible at the same time to carry out the simultaneous microorganisms destruction.

Food Handling↗
PubMed1992

The distribution of spontaneous mutations on quantitative traits and fitness in Drosophila melanogaster.

Starting from a completely homozygous population of Drosophila melanogaster, two groups of 100 inbred lines each were established and maintained for 46 generations, by a single brother-sister mating and two double first cousin matings, respectively. Sternopleural bristle number, wing length and wing width were simultaneously scored in all lines every 4-5 generations. The means of four lines in each group departed significantly from the overall mean and, in each case, this was attributed to a single mutation of relatively large effect on at least one trait (0.3-1.4 environmental standard deviations in absolute value). Further analyses revealed widespread pleiotropy, similar gene action of a given mutation for all traits affected, and predominant additive action. No apparent association was found between the magnitudes of mutational effects on the traits and fitness. However, all recessive mutations were deleterious. The distribution of mutant effects was asymmetrical (positive for bristles and negative for wing measurements). Moreover, these distributions had a high variance and may be leptokurtic, due to the presence of major genes. Estimates of the ratio of new mutational variance to environmental variance ranged within (0.7-3.4) x 10(-3), those for wing measurements being generally larger. In agreement with theory, the rate of between-line differentiation was independent of population size.

Animals↗
PubMed1991

The genetic properties of homosexual copulation behavior in Tribolium castaneum: diallel analysis.

The rate of homosexual copulation has been defined as the ratio between the number of homosexual mountings and the total number of mountings (homo and heterosexual) performed by a Tribolium castaneum male during a period of 30 min. In a laboratory population, the average rate when a number of males (m) and females (k x m) are tested together has been estimated in each of the six situations defined by m = 2 and 10 and k = 0.5, 1, and 2, k being the sex ratio among scored individuals. Good agreement was found between the observed rates of homosexual copulation and those expected assuming random contacts between pairs of individuals totally indiscriminate with respect to sex. The genetic properties of the trait have been investigated by means of a diallel analysis of six highly inbred lines derived from the same population and their F1 crosses. Significant general and specific combining ability effects were detected. When noninbred females were used for testing, the rate of homosexual copulation is expected to be higher for inbred than for noninbred males. This prediction, implying the existence of inbreeding depression for the trait, also was confirmed by the data.

Alleles↗
PubMed1991

The response to artificial selection from new mutations in Drosophila melanogaster.

Twenty generations of divergent selection for abdominal bristle number were carried out starting from a completely homozygous population of Drosophila melanogaster. All lines were selected with the same proportion (20%) but at two different numbers of selected parents of each sex (5 or 25). A significant response to selection was detected in eight lines (out of 40) and, in most cases, it could be wholly attributed to a single mutation of relatively large effect (0.5-2 phenotypic standard deviations). The ratio of new mutational variance to environmental variance was estimated to be (0.33 +/- 0.11) X 10(-3). The distribution of mutant effects was asymmetrical, both with respect to bristle number (85% of it was negative) and to fitness (most detected bristle mutations were lethal or semilethal). Moreover, this distribution was leptokurtic, due to the presence of major genes. Gene action on bristles ranged from additive to completely recessive, no epistatic interactions being found. In agreement with theory, larger responses in each direction were achieved by those lines selected at greater effective population sizes. Furthermore, the observed divergence between lines selected in opposite directions was proportional to their effective size, as predicted for mutations of large effect.

Animals↗
PubMed1988

Competition and genotypic variability in Drosophila melanogaster.

It has been claimed that in competitive conditions larval viabilities of Drosophila melanogaster depend on the similarity of genotypes coexisting. Two types of experimental populations were established: homogeneous (low genotypic variability) and heterogeneous (high genotypic variability). Under conditions of moderate larval competition productivity was similar, in each although the developmental time was shorter in the heterogeneous series. Under conditions of high larval competition the productivity of heterogeneous populations exceeded that of the homogeneous and attained the adult stage in shorter period of time.

Animals↗