Chromosome interactions in Drosophila melanogaster. I. Viability studies.

The nature of fitness interactions is an important, yet unsolved, question in population genetics. We compare the egg-to-adult viability of individuals homozygous for either a second or a third chromosome with the viability of individuals homozygous for both chromosomes simultaneously. On the average, the viability of the two-chromosome homozygotes is somewhat greater than expected assuming that the fitnesses of the single-chromosome homozygotes interact in a multiplicative fashion. This result differs from previous observations that indicate either no significant deviations from the expectation or lower-than-expected average fitnesses for the double homozygotes.

Chromosome interactions in Drosophila melanogaster. II. Total fitness.

In a large experiment, using nearly 200 population cages, we have measured the fitness of Drosophila melanogaster homozygous (1) for the second chromosome, (2) for the third chromosome, and (3) for both chromosomes. Twenty-four second chromosomes and 24 third chromosomes sampled from a natural population were tested. The mean fitness of the homozygous flies is 0.081 +/- 0.014 for the second chromosome, 0.080 +/- 0.017 for the third chromosome, and 0.079 +/- 0.024 for both chromosomes simultaneously. Assuming that fitnesses are multiplicative (the additive fitness model makes no sense in the present case because of the large selection coefficients involved), the expected mean fitness of the homozygotes for both chromosomes is 0.0066; their observed fitness is more than ten times greater. Thus, it appears that synergistic interactions between loci are considerable; and that, consequently, the fitness function substantially departs from linearity. Two models are tentatively suggested for the fitness function: a "threshold" model and a "synergistic" model.--The experiments reported here confirm previous results showing that the concealed genetic load present in natural populations of Drosophila is sufficient to account for the selective maintenance of numerous polymorphisms (of the order of 1000).

Effect of training on accumulated oxygen deficit and shuttle run performance.

BACKGROUND: The purpose of the present study was to investigate changes in physiological, metabolic and performance parameters resulting from an intense 6 week training programme. METHODS: Sixteen volunteers were divided into a control (CN; 4 men and 2 women) and training group (TR; 6 men and 4 women). Laboratory measures included maximal aerobic power (VO2max), submaximal oxygen uptake (10.5 percent or 6 degrees treadmill inclination) and accumulated oxygen deficit (AOD). Performance was assessed during 20 metre shuttle run tests (PST, progressive shuttle run test; HIST, high intensity shuttle run test). RESULTS: TR improved their HIST performance (m) significantly compared with CN, identified by a significant "group-by-training" interaction (p<0.01). Similarly, AOD values improved more in TR compared with CN (p<0.01). There was a trend for TR to further reduce blood pH values after training compared with CN, although this decrease (approximately 0.05 units) did not attain statistical significance. The change in AOD was strongly correlated with the change in run time to exhaustion (r=0.76, p<0.01) and the change in estimated total work output (r=0.69, p<0.01) during 10.5 percent gradient running and modestly correlated with the change in HIST performance (r=0.49, p<0.05, assuming a directional test). CONCLUSIONS: The results of the present study suggest changes in the anaerobic capacity, determined as AOD, due to training may be reflected in corresponding changes in laboratory and field performance.

A comparison of the psychosocial needs of hospice patients with AIDS and those with other diagnoses.

We compared the amount of psychosocial support required and received by patients with AIDS and without AIDS at Cedar Valley Hospice, Waterloo, Iowa. Hospice patients with AIDS (N = 11) required significantly more psychosocial support than non-AIDS patients (N = 36) of the same average age. The amount of non-hospice social support--family, congregation, and neighbors--received by AIDS patients was significantly less than that received by those with other diagnoses due to a virtual lack of neighbor support. There were no significant differences in family or congregational support. The high level of family support and lack of neighbor support may have been a result of many (8) of the AIDS patients having moved back to the area to die. A survey of hospice staff showed they felt working with AIDS patients was both more time consuming and more stressful than working with patients with other diagnoses.