No abstract

It has previously been suggested that small sperm size may be an adaptation to achieve uniparental inheritance of organelles, and hence to prevent the spread of selfish cytoplasmic elements. Such an explanation for anisogamy implies a mechanism whereby the male gamete eliminates its own cytoplasm prior to fusion with the egg. A model has been presented demonstrating the invasion and persistence of a modifier that acts gametically to kill its own organelles. Here we show, however, that this model is far from robust; indeed, if any cost is associated with the modifier it cannot persist. We also show that despite an empirically demonstrated association between anisogamy and multicellularity, this result also applies if the analysis is applied in the multicellular case. This class of model contrasts with the majority of analyses in which the modifier kills off the incoming gamete’s organelles. We show that these models are highly robust, even if uniparental inheritance is imperfect.

Continuous infusion of recombinant factor VIII (rFVIII) is desirable in clinical settings in order to maintain haemostatic levels in a cost-effective manner. This study was designed to determine rFVIII stability over time using a minipump set-up, which has been employed by clinicians for continuous infusion of rFVIII. Vials from three lots of Kogenate (Bayer Corporation) were reconstituted in sterile water for injection, pooled and transferred to minipump infusion sets composed of either polyvinylchloride (Medex # IPR86/tube volume 0.5 mL) or polyethylene (McGraw S5904-52, tube and adapter volume 2.1 mL), and held in temperature-controlled rooms at 5 degrees C, 25 degrees C and 30 degrees C. Additional bags of rFVII were prepared with heparin (4 U mL-1), and maintained at 30 degrees C. rFVIII was infused at a rate of 1.0 mL h-1. Samples were analysed for rFVIII activity over a 7-day period at 0, 1, 15, 24, 78 and 168 h. Prior to the start of the timed study, rFVIII activity was measured in the lot pools and in the polyvinylchloride or polyethylene bags, and in the first flush volumes through the tubing. There was no difference in rFVIII activity measured in the pools compared to the bags. rFVIII levels in the initial 3-mL infusion through the tubing showed a slight decrease in activity compared to the initial level which amounted to an insignificant loss of activity for the polyvinylchloride tubing but a significant loss in the polyethylene tubing (approximately 10 IU absolute loss in polyvinylchloride vs. 100 IU loss in polyethylene). After an initial flush of 1.0 mL for polyvinylchloride and 5.0 mL for polyethylene, activity returned to baseline and subsequently remained stable for all time points and temperatures from 5-30 degrees C over the 7-day period. We conclude that the standard polyvinylchloride in polyethylene minipump bags and tubing provide excellent delivery and stability of rFVIII for continuous infusion with or without heparin, and can be used in hospital and ambulatory settings.

No abstract

Meiosis may have evolved gradually within the eukaryotes with the earliest forms having a one‐step meiosis. It has been speculated that the putative transition from a one‐step meiosis without recombination to one with recombination may have been stimulated by the invasion of Killer alleles. These imaginary selfish elements are considered to act prior to recombination. They prime for destruction (which occurs after cell division) the half of the cell on the opposite side of the meiotic spindle. Likewise the transition from one‐step to two‐step meiosis might have been stimulated by a subtly different sort of imaginary distorter allele, a SisterKiller. These are proposed to act after recombination. It has yet to be established that the presence of such distorter alleles could induce the transitions in question. To investigate these issues we have analysed the dynamics of a modifier (1) of recombination and (2) of the number of steps of meiosis, as they enter a population with one‐step meiosis. For the modifier of recombination, we find that invasion conditions are very broad and that persistence of Killer and modifier is likely through most parameter space, even when the recombination rate is low. However, if we allow a Killer element to mutate into one that is self‐tolerant, the modifier and the nonself‐tolerant alleles are typically both lost from the population. The modifier of the number of steps can invade if the SisterKiller acts at meiosis II. However, a SisterKiller acting at meiosis I, far from promoting the modifier’s spread, actually impedes it. In the former case the invasion is easiest if there is no recombination. The SisterKiller hypothesis therefore fails to provide a reasonable account of the evolution of two‐step meiosis with recombination. As before, the evolution of self‐tolerance on the part of the selfish element destroys the process. We conclude that the conditions under which SisterKillers promote the evolution of two‐step meiosis are very much more limited than originally considered. We also conclude that there is no universal agreement between ESS and modifier analyses of the same transitions.