Lack of degeneration of loci on the neo-Y chromosome of Drosophila americana americana

The extent of genetic degeneration of the neo-Y chromosome of Drosophila americana americana has been investigated. Three loci, coding for the enzymes enolase, phosphoglycerate kinase and alcohol dehydrogenase, have been localized to chromosome 4 of D. a. americana, which forms the neo-Y and neo-X chromosomes. Crosses between D.a. americana and D. virilis or D. montana showed that the loci coding for these enzymes carry active alleles on the neo-Y chromosome in all wild-derived strains of americana that were tested. Intercrosses between a genetically marked stock of virilis and strains of americana were carried out, creating F3 males that were homozygous for sections of the neo-Y chromosome. The sex ratios in the F3 generation of the intercrosses showed that no lethal alleles have accumulated on any of the neo-Y chromosomes tested. There was evidence for more minor reductions in fitness, but this seems to be mainly caused by deleterious alleles that are specific to each strain. A similar picture was provided by examination of the segregation ratios of two marker genes among the F3 progeny. Overall, the data suggest that the neo-Y chromosome has undergone very little degeneration, certainly not to the extent of having lost the functions of vital genes. This is consistent with the recent origin of the neo-Y and neo-X chromosomes, and the slow rates at which the forces that cause Y chromosome degeneration are likely to work.

Relative dilution spaces of 2H- and 18O-labeled water in humans

The doubly labeled water method for measuring energy expenditure can be very sensitive to small differences in the ratio of the 2H to 18O isotope dilution spaces. Recently it has been suggested that the average ratio is higher than the 1.03 we previously recommended. We therefore combined the data from 99 recently studied subjects. Subjects (85 females and 14 males) were between the ages of 4 and 78 yr (mean = 34 yr) and between 10 and 52% (mean = 35%) fat. The average 2H-to-18O dilution space ratio was 1.034 +/- 0.014, which was very similar to the original assumption. As in recent reports, we did find that most of the variance (60%) was due to random analytic error and that there was no correlation between the dilution space ratio and age or body fat. However, in contrast to recent reports we found no evidence of a gender difference. Use of the constant dilution space ratio of 1.034 to recalculate CO2 product in published validation studies demonstrated improved accuracy, and thus the value of 1.034 is suggested for use in future studies.

Total daily energy expenditure and activity level in anorexia nervosa

Clinical reports consistently comment on high physical activity for anorexia nervosa patients but provide few quantitative measurements. To assess activity, total daily energy expenditure (TDEE) by doubly labeled water, basal metabolic rate (BMR), and thermic effect of meals (TEM) were measured in six female outpatients with anorexia nervosa (67% of ideal body weight) and age-, sex-, and height-matched to six control subjects. Anorexia nervosa patients expended more energy as physical activity than did control subjects [0.084 +/- 0.012 vs 0.044 +/- 0.008 MJ/kg body wt, respectively (20.1 +/- 3.0 vs 10.5 +/- 1.9 kcal/kg body wt, respectively), P less than 0.04], although they had a lower BMR [4.17 +/- 0.37 vs 5.52 +/- 0.15 MJ/d, respectively (997 +/- 89 vs 1319 +/- 37 kcal/d, respectively), P less than 0.01]. TDEE and TEM were similar in both groups. There was a reduction in serum triiodothyronine (T3; 1.20 +/- 0.15 vs 2.04 +/- 0.13 nmol/L, respectively; P less than 0.003) and a slight reduction in serum thyroxine (T4); reverse T3, thyrotropin, free T4, serum cortisol, and adrenocorticotropin values were normal. BMR correlated with total body weight and fat-free mass. These results provide quantitative evidence for increased physical activity in anorexia nervosa despite profound underweight and hypometabolism.