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L Varona

Publications and source records attributed to L Varona.

At least 55 records · Page 3Linked to original sources
PubMed1998

Estimation of dominance variance in purebred Yorkshire swine.

We used 179,485 Yorkshire reproductive and 239,354 Yorkshire growth records to estimate additive and dominance variances by Method Fraktur R. Estimates were obtained for number born alive (NBA), 21-d litter weight (LWT), days to 104.5 kg (DAYS), and backfat at 104.5 kg (BF). The single-trait models for NBA and LWT included the fixed effects of contemporary group and regression on inbreeding percentage and the random effects mate within contemporary group, animal permanent environment, animal additive, and parental dominance. The single-trait models for DAYS and BF included the fixed effects of contemporary group, sex, and regression on inbreeding percentage and the random effects litter of birth, dam permanent environment, animal additive, and parental dominance. Final estimates were obtained from six samples for each trait. Regression coefficients for 10% inbreeding were found to be -.23 for NBA, -.52 kg for LWT, 2.1 d for DAYS, and 0 mm for BF. Estimates of additive and dominance variances expressed as a percentage of phenotypic variances were, respectively, 8.8 +/- .5 and 2.2 +/- .7 for NBA, 8.1 +/- 1.1 and 6.3 +/- .9 for LWT, 33.2 +/- .4 and 10.3 +/- 1.5 for DAYS, and 43.6 +/- .9 and 4.8 +/- .7 for BF. The ratio of dominance to additive variances ranged from .78 to .11.

Adipose Tissue↗
PubMed1998

Effect of full sibs on additive breeding values under the dominance model for stature in United States Holsteins.

Differences in breeding values between dominance and additive models were examined theoretically and with field data. Data included 5.2 million records on stature from 3.0 million US Holsteins. The largest full-sib family had 29 animals, and 7% of all animals had at least one full sib. The dominance model, which accounted for dominance covariances, included the following effects: management, age, stage of lactation, permanent environment, animal additive, and parental dominance (one-quarter of dominance variance) as well as a regression coefficient for inbreeding percentage. Two reduced models were also assumed; in the first, the parental dominance effect was removed, and, in the second, the inbreeding regression coefficient was also removed. The correlations between breeding values in the three models were > 0.999, but breeding values of some animals from full-sib families changed > 5 standard deviations of parental dominance. The largest changes were observed for parents with large numbers of full-sib progeny, with limited information from parents, and without individual performance records. On average, the differences were up to four times larger for cows than for bulls and up to five times larger for dams than for sires. The greatest differences in breeding values between the dominance and the additive models were observed for dams with full-sib progeny, female full sibs, and low reliability bulls with full sibs in the extended family. Animals with large amounts of additive information as progeny-tested bulls were influenced little by the inclusion of dominance. Animals with a large proportion of information coming from animals with dominance relationships, such as cows originating via embryo transfer changed the most.

Animals↗
PubMed1998

Bayesian analysis of Wood's lactation curve for Spanish dairy cows.

A Bayesian procedure is presented to analyze test day performances in the scope of Wood's lactation function: atb (exp (-ct)), where a, b, and c = parameters, and t = time-dependent variable. The procedure has been applied to 148,557 test day controls corresponding to records for 15,349 first lactations of Spanish dairy cows. The procedure uses all available information and reduces the presence of atypical lactations. Moreover, the posterior marginal distribution of (co)variance components, breeding values, and systematic effects for the underlying variables of Wood's function are provided. The posterior means of the heritabilities were 0.43, 0.17, 0.40, and 0.29 for the parameters a (initial milk yield), b (ascent to peak), c (descent from peak), and total milk yield, respectively. Selection for total milk yield implies a great effect on the initial milk yield (a) but only minor effects on ascent to peak (b) and descent from peak (c).

Aging↗
PubMed1998

[Idiopathic cervical plexopathy].

We describe a 26 year-old woman with cervical plexopathy with damage of left superficial or cutaneous branches, and left cervical sensory dorsal rami. Picture began acutely and vanished few days later. We ruled out known etiologies like traumatisms, tumours and surgical and anaesthetic complicated procedures, therefore the patient suffered an idiopathic cervical plexopathy. We hypothesize two possibilities for this clinical picture: an autoimmune reaction or a muscular entrapment.

Acute Disease↗
PubMed1995

[Posterior cortical atrophy with progressive visual agnosia].

Interest in progressive focal cerebral syndromes associated with classical degenerative diseases has increased in recent years. Descriptions of posterior cortical atrophy with progressive visual agnosia are relatively rare. We present 5 patients (2 women) ranging in age between 57 and 72 years old. In all cases symptoms began and progressed with no known etiology. All cases were sporadic. The main clinical signs are difficulty in recognizing objects, colors, persons or places; topographical disorientation and visual memory alterations; alexia, simultagnosia, loss of ocular fixing and optic ataxia. Some patients presented other disturbances of praxis or memory and 2 progressed to global dementia. Language function was preserved and behavioral disturbances did not develop. The amplitude of the P100 visual evoked potential was low but latency was normal in 4 patients and prolonged in 1. Brain images showed atrophy and hypoperfusion in the parieto-occipital area. The neuropathology status of these patients is unknown.

Adult↗
PubMed1995

[Spontaneous internal carotid artery dissection as a cause of unilateral lower cranial nerve palsies].

We present a 60-year-old man with a complete right IX-XII nerve palsy (Collet-Sicard syndrome) due to spontaneous right internal carotid artery (ICA) dissection. Magnetic resonance imaging (MRI) and MR angiography (MRA) showed signs of subadventitial dissection of the right ICA with a mural haematoma that expanded the circumference of the vessel at the level of the retrostyloid space, adjacent to the IX-XII nerves. No narrowing of the lumen or aneurysms was found. Clinical recovery was excellent after treatment with only antiplatelet drugs. Cervical internal carotid artery dissection should be included in the differential diagnosis of lower cranial nerve palsies. MRI and MRA are noninvasive, reliable methods for diagnosis and follow-up, especially in subadventitial dissections.

Bulbar Palsy, Progressive↗
PubMedDate not supplied

Computation of identity by descent probabilities conditional on DNA markers via a Monte Carlo Markov Chain method.

The accurate estimation of the probability of identity by descent (IBD) at loci or genome positions of interest is paramount to the genetic study of quantitative and disease resistance traits. We present a Monte Carlo Markov Chain method to compute IBD probabilities between individuals conditional on DNA markers and on pedigree information. The IBDs can be obtained in a completely general pedigree at any genome position of interest, and all marker and pedigree information available is used. The method can be split into two steps at each iteration. First, phases are sampled using current genotypic configurations of relatives and second, crossover events are simulated conditional on phases. Internal track is kept of all founder origins and crossovers such that the IBD probabilities averaged over replicates are rapidly obtained. We illustrate the method with some examples. First, we show that all pedigree information should be used to obtain line origin probabilities in F2 crosses. Second, the distribution of genetic relationships between half and full sibs is analysed in both simulated data and in real data from an F2 cross in pigs.

Journal Article↗
PubMedDate not supplied

Hypothesis testing for the genetic background of quantitative traits.

The testing of Bayesian point null hypotheses on variance component models have resulted in a tough assigmment for which no clear and generally accepted method exists. In this work we present what we believe is a succeeding approach to such a task. It is based on a simple reparameterization of the model in terms of the total variance and the proportion of the additive genetic variance with respect to it, as well as on the explicit inclusion on the prior probability of a discrete component at origin. The reparameterization was used to bypass an arbitrariness related to the impropriety of uninformative priors onto unbounded variables while the discrete component was necessary to overcome the zero probability assigned to sets of null measure by the usual continuous variable models. The method was tested against computer simulations with appealing results.

Algorithms↗
PubMedDate not supplied

Bayes factors for detection of quantitative trait loci.

A fundamental issue in quantitative trait locus (QTL) mapping is to determine the plausibility of the presence of a QTL at a given genome location. Bayesian analysis offers an attractive way of testing alternative models (here, QTL vs. no-QTL) via the Bayes factor. There have been several numerical approaches to computing the Bayes factor, mostly based on Markov Chain Monte Carlo (MCMC), but these strategies are subject to numerical or stability problems. We propose a simple and stable approach to calculating the Bayes factor between nested models. The procedure is based on a reparameterization of a variance component model in terms of intra-class correlation. The Bayes factor can then be easily calculated from the output of a MCMC scheme by averaging conditional densities at the null intra-class correlation. We studied the performance of the method using simulation. We applied this approach to QTL analysis in an outbred population. We also compared it with the Likelihood Ratio Test and we analyzed its stability. Simulation results were very similar to the simulated parameters. The posterior probability of the QTL model increases as the QTL effect does. The location of the QTL was also correctly obtained. The use of meta-analysis is suggested from the properties of the Bayes factor.

Algorithms↗