Extensive heterosis in growth of yeast hybrids is explained by a combination of genetic models.

Heterosis, also known as hybrid vigor, is the superior performance of a heterozygous hybrid relative to its homozygous parents. Despite the scientific curiosity of this phenotypic phenomenon and its significance for food production in agriculture, its genetic basis is insufficiently understood. Studying heterosis in yeast can potentially yield insights into its genetic basis, can allow one to test the different hypotheses that have been proposed to explain the phenomenon and allows better understanding of how to take advantage of this phenomenon to enhance food production. We therefore crossed 16 parental yeast strains to form 120 yeast hybrids, and measured their growth rates under five environmental conditions. A considerable amount of dominant genetic variation was found in growth performance, and heterosis was measured in 35% of the hybrid-condition combinations. Despite previous reports of correlations between heterosis and measures of sequence divergence between parents, we detected no such relationship. We used several analyses to examine which genetic model might explain heterosis. We found that dominance complementation of recessive alleles, overdominant interactions within loci and epistatic interactions among loci each contribute to heterosis. We concluded that in yeast heterosis is a complex phenotype created by the combined contribution of different genetic interactions.

Accidental injuries are more common in children with attention deficit hyperactivity disorder compared with their non-affected siblings.

BACKGROUND: Accidental injuries are a leading cause of paediatric morbidity and mortality. We hypothesized that attention deficit hyperactivity disorder (ADHD), a common childhood disorder characterized by behaviours such as hyperactivity and impulsivity, is a risk factor for accidental injuries. Previous retrospective studies suggested that children with ADHD have an increased injury rate, but controlled prospective studies are lacking. METHODS: We conducted a prospective case-control study of 29 school-aged children with ADHD and their same-sex, similarly aged, non-ADHD-affected siblings. All diagnoses were made by a paediatric neurologist according to DSM-IV criteria and the children and their parents underwent a structured psychiatric interview and a battery of complementary assessments including: Child Behavior Checklist (CBCL), ADHD Rating scale and Developmental Coordination Disorder Questionnaire (DCDQ). The parents were contacted by telephone every 3 months during a 9-month follow-up period and all injuries requiring medical attention were recorded. Incidence of injuries was compared between the pairs of siblings. RESULTS: During the follow-up period, a total of 13 injuries in 13 children with ADHD were reported, compared with six injuries in six children from the control group (Z=-2.11, P < 0.05). ADHD severity and subtype, CBCL, DCDQ and IQ scores were not predictive of injury risk. CONCLUSIONS: School-aged children with ADHD are at higher risk of accidental injuries than their non-ADHD siblings, regardless of ADHD subtype, co-morbid psychiatric conditions, developmental co-ordination problems and environmental/familial conditions. Awareness and adequate education of parents and caregivers of children with ADHD concerning the increased injury risks are thus warranted.

The Variability of Seyfert 1.8 and 1.9 Galaxies at 1.6 Microns.

We present a study of Seyfert 1.5-2.0 galaxies observed at two epochs with the Hubble Space Telescope (HST) at 1.6 µm. We find that unresolved nuclear emission from nine of 14 nuclei varies at the level of 10%-40% on timescales of 0.7-14 months, depending upon the galaxy. A control sample of Seyfert galaxies lacking unresolved sources and galaxies lacking Seyfert nuclei show less than 3% instrumental variation in equivalent aperture measurements. This proves that the unresolved sources are nonstellar and associated with the central parsecs of active galactic nuclei. Unresolved sources in Seyfert 1.8 and 1.9 galaxies are not usually detected in HST optical surveys; however, high angular resolution infrared observations will provide a way to measure time delays in these galaxies.

Doctor-patient communication in a cancer ward.

This study explored doctor-patient interaction by focusing on a specific type of encounter in an oncology ward, designed to enable discussion of the case by the doctors and informing the patient. In line with the cognitive orientation theory of Kreitler and Kreitler, the encounter's effects were examined in regard to three aspects--disease, treatment, and general state--on four levels: the information the patients have, their feelings, the information they desire, and the information they consider desirable. The patients were 52 men and women with different cancer diagnoses. Comparable questionnaires were administered to the patients before and after the meeting, and to the doctors only after it. The patients responded before and after also to Spielberger's scales of state anxiety and state anger. The results showed that patients claimed they had gained hardly any new information concerning the disease and their overall state. There were no decreases in the desired and desirable information. Their feelings were affected negatively to a slight extent, especially concerning treatment. In a quarter of the subjects, anxiety decreased and was replaced by anger. In regard to all levels and aspects there was a large gap between the evaluations of doctors and patients. The major conclusions were that patients and doctors differ in the meaning they assign to information, and that patients are conflicted in regard to asking for the personally relevant information they want.