Antagonistic pleiotropy can maintain fitness variation in annual plants.

Antagonistic pleiotropy (AP) is a genetic trade-off between different fitness components. In annual plants, a trade-off between days to flower (DTF) and reproductive capacity often determines how many individuals survive to flower in a short growing season, and also influences the seed set of survivors. We develop a model of viability and fecundity selection informed by many experiments on the yellow monkeyflower, Mimulus guttatus, but applicable to many annual species. A viability/fecundity trade-off maintains stable polymorphism under surprisingly general conditions. We also introduce both spatial heterogeneity and temporal stochasticity in environmental parameters. Neither is necessary for polymorphism, but spatial heterogeneity allows polymorphism while also generating the often observed non-negative correlations in fitness components.

Sanitizing in Dry-Processing Environments Using Isopropyl Alcohol Quaternary Ammonium Formula.

Dry-processing environments are particularly challenging to clean and sanitize because introduced water can favor growth and establishment of pathogenic microorganisms such as Salmonella. Our objective was to determine the efficacy of an isopropyl alcohol quaternary ammonium (IPAQuat) formula for eliminating potential Salmonella contamination on food contact surfaces. Clean stainless steel coupons and conveyor belt materials used in dry-processing environments were spot inoculated in the center of coupons (5 by 5 cm) with a six-serotype composite of Salmonella (approximately 10 log CFU/ml), subjected to IPAQuat sanitizer treatments with exposure times of 30 s, 1 min, or 5 min, and then swabbed for enumeration of posttreatment survivors. A subset of inoculated surfaces was soiled with a breadcrumb-flour blend and allowed to sit on the laboratory bench for a minimum of 16 h before sanitation. Pretreatment Salmonella populations (inoculated controls, 0 s treatment) were approximately 7.0 log CFU/25 cm(2), and posttreatment survivors were 1.31, 0.72, and < 0.7 (detection limit) log CFU/25 cm(2) after sanitizer exposure for 30 s, 1 min, or 5 min, respectively, for both clean (no added soil) and soiled surfaces. Treatment with the IPAQuat formula using 30-s sanitizer exposures resulted in 5.68-log reductions, whereas >6.0-log reductions were observed for sanitizer exposures of 1 and 5 min. Because water is not introduced into the processing environment with this approach, the IPAQuat formula could have sanitation applications in dry-processing environments to eliminate potential contamination from Salmonella on food contact surfaces.

Advanced oxidation technology with photohydroionization as a surface treatment for controlling Listeria monocytogenes on stainless steel surfaces and ready-to-eat cheese and turkey.

Listeria monocytogenes is difficult to control in food and processing environments due to its widespread nature and ability to survive in a range of adverse conditions, including low temperatures, pH, and high salt concentrations. The objective of this study was to evaluate the efficacy of Photohydroionization™ (PHI; RGF Environmental Group, Inc., Riviera, Beach, FL), a novel advanced oxidation technology, as a surface treatment to control L. monocytogenes on food-contact surfaces, sliced American cheese, and ready-to-eat (RTE) turkey. A five-strain cocktail of L. monocytogenes was used to inoculate sample surfaces. Food-contact surfaces were exposed to ultraviolet and other oxidative gases produced by the PHI system for 10, 20, 30, 45, 60, and 120 s and 5, 10, and 15 min; cheese and turkey samples were treated for 30, 60, and 120 s and 5 min. For each matrix at each time point, seven samples were treated and enumerated by plating appropriate dilutions onto modified oxford medium and thin-agar-layer modified oxford medium. Results showed reductions (p<0.05) in L. monocytogenes: 4.37 log colony-forming units (CFU)/coupon on stainless steel after 15-min treatment. A 1.39 and 1.63 log CFU/sample after 120 s and 2.16 and 2.52 log CFU/sample after 5 min were seen on American cheese and ready-to-eat turkey, respectively. Lipid oxidation analyses performed on cheese and turkey samples indicated that PHI treatment did not affect (p>0.05) thiobarbituric acid-reactive substances values. This study demonstrates the efficacy of PHI treatment to reduce L. monocytogenes on stainless steel and RTE foods and may serve as a processing intervention to ensure safe production of food.

Natural antioxidants in meat and poultry products.

In response to recent claims that synthetic antioxidants have the potential to cause toxicological effects and consumers' increased interest in purchasing natural products, the meat and poultry industry has been seeking sources of natural antioxidants. Due to their high phenolic compound content, fruits and other plant materials provide a good alternative to conventional antioxidants. Plum, grape seed extract, cranberry, pomegranate, bearberry, pine bark extract, rosemary, oregano, and other spices functions as antioxidants in meat and poultry products. Pomegranate, pine bark extract, cinnamon, and cloves have exhibited stronger antioxidant properties than some synthetic options. Plum products, grape seed extract, pine bark extract, rosemary, and some spices all have been shown to affect the color of finished meat or poultry products; however, in some products such as pork sausage or uncured meats, an increase in red color may be desired. When selecting a natural antioxidant, sensory and quality impact on the product should be considered to achieve desired traits.

Effect of salt reduction on growth of Listeria monocytogenes in meat and poultry systems.

Reducing sodium in food could have an effect on food safety. The objective was to determine differences in growth of Listeria monocytogenes in meat and poultry systems with salt substitutes. For phase 1, fresh ground beef, pork, and turkey with NaCl, KCl, CaCl(2), MgCl(2), sea salt, or replacement salt added at 2.0% were inoculated with L. monocytogenes to determine growth/survival during 5 d at 4 °C to simulate a pre-blend process. L. monocytogenes populations significantly decreased (0.41 log CFU/g) during the storage time in beef, but no differences (P > 0.05) were observed over time in pork or turkey. Salt type did not affect (P > 0.05) L. monocytogenes populations during pre-blend storage. MgCl(2) and NaCl allowed significant growth of aerobic populations during storage. For phase 2, emulsified beef and pork products were processed with 2% NaCl, KCl, sea salt, or a NaCl/KCl blend and post-process surface-inoculated with L. monocytogenes to determine growth/survival at 4 °C for 28 d. Pork products showed significantly greater L. monocytogenes population growth at all sampling times (0, 7, 14, 21, and 28 d) than beef products, but salt type had no effect on L. monocytogenes populations with sampling times pooled for data analysis. Although salt types had no impact on L. monocytogenes populations in preblend and emulsified meat products, pork and turkey preblends and emulsified pork had greater L. monocytogenes populations compared with beef products. These studies demonstrate that sodium may not affect the safety of preblends and emulsified meat and poultry products.

A Bayesian method for the joint estimation of outcrossing rate and inbreeding depression.

The population outcrossing rate (t) and adult inbreeding coefficient (F) are key parameters in mating system evolution. The magnitude of inbreeding depression as expressed in the field can be estimated given t and F via the method of Ritland (1990). For a given total sample size, the optimal design for the joint estimation of t and F requires sampling large numbers of families (100-400) with fewer offspring (1-4) per family. Unfortunately, the standard inference procedure (MLTR) yields significantly biased estimates for t and F when family sizes are small and maternal genotypes are unknown (a common occurrence when sampling natural populations). Here, we present a Bayesian method implemented in the program BORICE (Bayesian Outcrossing Rate and Inbreeding Coefficient Estimation) that effectively estimates t and F when family sizes are small and maternal genotype information is lacking. BORICE should enable wider use of the Ritland approach for field-based estimates of inbreeding depression. As proof of concept, we estimate t and F in a natural population of Mimulus guttatus. In addition, we describe how individual maternal inbreeding histories inferred by BORICE may prove useful in studies of inbreeding and its consequences.

Effect of packaging and storage time on survival of Listeria monocytogenes on kippered beef steak and turkey tenders.

UNLABELLED: The objective of our study was to determine effect of packaging method and storage time on reducing Listeria monocytogenes in shelf-stable meat snacks. Commercially available kippered beef steak strips and turkey tenders were dipped into a 5-strain L. monocytogenes cocktail, and dried at 23 °C until a water activity of 0.80 was achieved. Inoculated samples were packaged with 4 treatments: (1) vacuum, (2) nitrogen flushed with oxygen scavenger, (3) heat sealed with oxygen scavenger, and (4) heat sealed without oxygen scavenger. Samples were stored at 23 °C and evaluated for L. monocytogenes levels at 0, 24, 48, and 72 h. Initial levels (time 0) of L. monocytogenes were approximately 5.7 log CFU/cm² for steak and tenders. After 24 h of storage time, a 1 log CFU/cm² reduction of L. monocytogenes was observed for turkey tenders for all packaging treatments. After 48 h, turkey tenders showed >1 log CFU/cm² reduction of L. monocytogenes for all packaging treatments except for vacuum, where only 0.9 log CFU/cm² reduction was observed. After 72 h, reductions for all packaging treatments for turkey tenders ranged from 1.5 to 2.4 log CFU/cm². For kippered beef steak, there was no interaction between the packaging treatments and all storage times (P > 0.05) whereas, time was different (P <0.05). For kippered beef steak, there was 1 log reduction of L. monocytogenes at 24 and 48 h of storage times at 23 °C for all packaging treatments and a 2.1 log CFU/ cm² L. monocytogenes reduction at 72 h of storage time. PRACTICAL APPLICATIONS: Processors of kippered beef steak and turkey tenders could use a combination of vacuum or nitrogen-flushing or heat sealed with an oxygen scavenger packaging methods and a holding time of 24 h prior to shipping to reduce potential L. monocytogenes numbers by ≥1 log. However, processors should be encouraged to hold packaged product a minimum of 72 h to enhance the margin of safety for L. monocytogenes control.

Comparing the mannitol-egg yolk-polymyxin agar plating method with the three-tube most-probable-number method for enumeration of Bacillus cereus spores in raw and high-temperature, short-time pasteurized milk.

The U.S. Food and Drug Administration's Bacteriological Analytical Manual recommends two enumeration methods for Bacillus cereus: (i) standard plate count method with mannitol-egg yolk-polymyxin (MYP) agar and (ii) a most-probable-number (MPN) method with tryptic soy broth (TSB) supplemented with 0.1% polymyxin sulfate. This study compared the effectiveness of MYP and MPN methods for detecting and enumerating B. cereus in raw and high-temperature, short-time pasteurized skim (0.5%), 2%, and whole (3.5%) bovine milk stored at 4°C for 96 h. Each milk sample was inoculated with B. cereus EZ-Spores and sampled at 0, 48, and 96 h after inoculation. There were no differences (P > 0.05) in B. cereus populations among sampling times for all milk types, so data were pooled to obtain overall mean values for each treatment. The overall B. cereus population mean of pooled sampling times for the MPN method (2.59 log CFU/ml) was greater (P < 0.05) than that for the MYP plate count method (1.89 log CFU/ml). B. cereus populations in the inoculated milk samples ranged from 2.36 to 3.46 and 2.66 to 3.58 log CFU/ml for inoculated milk treatments for the MYP plate count and MPN methods, respectively, which is below the level necessary for toxin production. The MPN method recovered more B. cereus, which makes it useful for validation research. However, the MYP plate count method for enumeration of B. cereus also had advantages, including its ease of use and faster time to results (2 versus 5 days for MPN).

Package systems and storage times serve as postlethality controls for Listeria monocytogenes on whole-muscle beef jerky and pork and beef smoked sausage sticks.

To validate how packaging and storage reduces Listeria monocytogenes on whole-muscle beef jerky and smoked pork and beef sausage sticks, four packaging systems (heat sealed [HS] without vacuum, heat sealed with oxygen scavenger, nitrogen flushed with oxygen scavenger [NFOS], and vacuum) and four ambient temperature storage times were evaluated. Commercially available whole-muscle beef jerky and smoked pork and beef sausage sticks were inoculated with a five-strain L. monocytogenes cocktail, packaged, and then stored at 25.5 °C until enumerated for L. monocytogenes at 0, 24, 48, and 72 h and 30 days after packaging. The interaction of packaging and storage time affected L. monocytogenes reduction on jerky, but not on sausage sticks. A >2-log CFU/cm(2) reduction was achieved on sausage sticks after 24 h of storage, regardless of package type, while jerky had <2-log reductions for all packaging types. At 48 h, log reductions were similar (P. 0.05) for all types of jerky packaging, ranging from 1.26 to 1.72 log CFU/cm(2); however, at 72 h, mean L. monocytogenes reductions were >2 log CFU/cm(2), except for NFOS (1.22-log CFU/cm(2) reduction). Processors could package beef jerky in HS packages with oxygen scavenger or vacuum in conjunction with a 24-h holding time as an antimicrobial process to ensure a >1-log CFU/cm(2) L. monocytogenes reduction or use a 48-h holding time for HS- or NFOS-packaged beef jerky. A >3-log CFU/cm(2) mean reduction was observed for all beef jerky and sausage stick packaging systems after 30 days of 25.5 °C storage.

Evaluation of two thermal processing schedules at low relative humidity for elimination of Escherichia coli O157:H7 and Salmonella serovars in chopped and formed beef jerky.

Foodborne outbreaks have been linked to jerky produced under insufficient thermal processing schedules. Reduction of Escherichia coli O157:H7 and Salmonella serovars during thermal processing of chopped and formed beef jerky was evaluated under two processing schedules representative of those used by large-scale (LS) and small-scale (SS) jerky production facilities. Fresh chopped and formed all-beef jerky batter was inoculated with 5.8 to 7.3 log CFU of E. coli O157:H7 or Salmonella per g, extruded into strips, and thermally processed by LS or SS schedules. A >or=5.0-log CFU/g reduction of both pathogens occurred with <10% relative humidity and a cumulative process of 44 min at 55.6 degrees C followed by 46 min at 77.8 degrees C into the LS schedule. Additional drying at 77.8 degrees C for 3.5 h was needed to achieve a water activity of 0.67 and a moisture-to-protein ratio (MPR) of 0.77. For the SS process, a >or=5.0-log CFU/g reduction of both pathogens occurred with 15 to 20% relative humidity and a cumulative process of 45 min at 52 degrees C, 60 min at 57 degrees C, 45 min at 60 degrees C, 45 min at 63 degrees C, 90 min at 68 degrees C, and finishing with 30 min at 77 degrees C. After processing for an additional 90 min at 77 degrees C, water activity was 0.60 while the MPR was 0.82. The LS and SS processes for producing chopped and formed jerky provided >or=5.0 log lethality to control E. coli O157:H7 and Salmonella. However, both processes would require additional drying to achieve an MPR of 0.75 to be labeled as jerky.

Inbreeding depression in an asexual population of Mimulus guttatus.

The reproductive mechanism, that is whether an organism outcrosses, selfs or asexually reproduces, has a substantial impact on the amount and pattern of genetic variation. In this study, we estimate genetic variation and genetic load for a predominately asexual population of Mimulus guttatus, and then compare our results to other studies of predominately sexually reproducing (outcrossing and selfing) populations of M. guttatus. The asexual population had low levels of heterozygosity (H(e) = 0.03) and low (but significantly non-zero) inbreeding load, especially when compared with other M. guttatus populations. This differs greatly from the sexual populations of Mimulus that display substantial inbreeding depression. We discuss a variety of reasons why we see such low load in this study and suggest future research projects to further explore the questions.

Inhibition of thromboxane A2-induced arrhythmias and intracellular calcium changes in cardiac myocytes by blockade of the inositol trisphosphate pathway.

We have recently reported that left atrial injections of the thromboxane A(2) (TXA(2)) mimetic, (5Z)-7-[(1R,4S,5S,6R)-6-[(1E,3S)-3-hydroxy-1-octenyl]-2 -oxabicyclo[2.2.1]hept-5-yl]-5-heptenoic acid (U46619), induced ventricular arrhythmias in the anesthetized rabbit. Data from this study led us to hypothesize that TXA(2) may be inducing direct actions on the myocardium to induce these arrhythmias. The aim of this study was to further elucidate the mechanism responsible for these arrhythmias. We report that TXA(2)R is expressed at both the gene and protein levels in atrial and ventricular samples of adult rabbits. In addition, TXA(2)R mRNA was identified in single, isolated ventricular cardiac myocytes. Furthermore, treatment of isolated cardiac myocytes with U46619 increased intracellular calcium in a dose-dependent manner and these increases were blocked by the specific TXA(2)R antagonist, 7-(3-((2-((phenylamino)carbonyl)hydrazino)methyl)-7-oxabicyclo(2.2.1)hept-2-yl)-5-heptenoic acid (SQ29548). Pretreatment of myocytes with an inhibitor of inositol trisphosphate (IP(3)) formation, gentamicin, or with an inhibitor of IP(3) receptors, 2-aminoethoxydiphenylborate (2-APB), blocked the increase in intracellular calcium. In vivo pretreatment of anesthetized rabbits with either gentamicin or 2-APB subsequently inhibited the formation of ventricular arrhythmias elicited by U46619. These data support the hypothesis that TXA(2) can induce arrhythmias via a direct action on cardiac myocytes. Furthermore, these arrhythmogenic actions were blocked by inhibitors of the IP(3) pathway. In summary, this study provides novel evidence for direct TXA(2)-induced cardiac arrhythmias and provides a rationale for IP(3) as a potential target for the treatment of TXA(2)-mediated arrhythmias.

Direct estimation of the mutation rate at dinucleotide microsatellite loci in Arabidopsis thaliana (Brassicaceae).

The mutation rate at 54 perfect (uninterrupted) dinucleotide microsatellite loci is estimated by direct genotyping of 96 Arabidopsis thaliana mutation accumulation lines. The estimated rate differs significantly among motif types with the highest rate for AT repeats (2.03 x 10(-3) per allele per generation), intermediate for CT (3.31 x 10(-4)), and lowest for CA (4.96 x 10(-5)). The average mutation rate per generation for this sample of loci is 8.87 x 10(-4) (s.e.=2.57 x 10(-4)). There is a strong effect of initial repeat number, particularly for AT repeats, with mutation rate increasing with the length of the microsatellite locus in the progenitor line. Controlling for motif and initial repeat number, chromosome 4 exhibited an elevated mutation rate relative to other chromosomes. The great majority of mutations were gains or losses of a single repeat. Generally, the data are consistent with the stepwise mutation model of microsatellite evolution. Several lines exhibited multiple step changes from the progenitor sequence, but it is unclear whether these are multi-step mutations or multiple single-step mutations. A survey of dinucleotide repeats across the entire Arabidopsis genome indicates that AT repeats are most abundant, followed by CT, and CA.

The genetic consequences of fluctuating inbreeding depression and the evolution of plant selfing rates.

The magnitude of inbreeding depression, a central parameter in the evolution of plant mating systems, can vary depending on environmental conditions. However, the underlying genetic mechanisms causing environmental fluctuations in inbreeding depression, and the consequences of this variation for the evolution of self-fertilization, have been little studied. Here, we consider temporal fluctuations of the selection coefficient in an explicit genetic model of inbreeding depression. We show that substantial variance in inbreeding depression can be generated at equilibrium by fluctuating selection, although the simulated variance tends to be lower than has been measured in experimental studies. Our simulations also reveal that purging of deleterious mutations does not depend on the variance in their selection coefficient. Finally, an evolutionary analysis shows that, in contrast to previous theoretical approaches, intermediate selfing rates are never evolutionarily stable when the variation in inbreeding depression is due to fluctuations in the selection coefficient on deleterious mutations.

The genetic analysis of family structured inbreeding depression studies.

An important question emerging from theoretical studies of mating system evolution is whether the fitness of a randomly extracted, fully inbred genotype will exceed the mean of outbred individuals. We introduce two statistics (I(1) and I(2)) related to the probability of extracting a high line. I(1) and I(2) can be estimated from the family structured experimental designs typically used to estimate inbreeding depression (ID). Maximum likelihood procedures are developed from an explicit genetic model. These yield parameter estimates and provide the likelihoods necessary to test hypotheses, for example, whether population-level ID is nonzero. Finally, we describe a new publicly available computer program titled 'IDG' (Inbreeding Depression Genetics) to execute these procedures.

Genotype x environment interaction for male attractiveness in an acoustic moth: evidence for plasticity and canalization.

The lek paradox arises when choosy females deplete the genetic variance for male display traits from a population, yet substantial additive genetic variation (V(A)) in male traits persists. Thus, the lek paradox can be more generally stated as one of the most fundamental evolutionary questions: What maintains genetic variation in natural populations? One solution to this problem may be found in the condition-dependent nature of many sexually selected traits. Genotype x environment (G x E) interactions can maintain V(A) under conditions of environmental heterogeneity provided certain restrictions are met, although antagonistic pleiotropy has also been proposed as a mechanism. Here, we provide evidence for G x E interactions and against the role of antagonistic pleiotropy in the maintenance of V(A) for sexually selected traits. Using inbred lines of the lesser waxmoth Achroia grisella, we measured V(A) for song attractiveness, condition and development rate under different competitive environments and found that genotypes differed in their plasticity. We argue that variation persists in natural populations because G x E interactions prevent any one variant from producing the optimal phenotype across all environments.

Development and characterization of an antimicrobial packaging film coating containing nisin for inhibition of Listeria monocytogenes.

The purpose of this study was to develop and characterize a packaging film coating containing nisin. A spot-on-lawn assay was used to determine the effect of acid type (ascorbic, acetic, hydrochloric, lactic) and nisin level (equal increments from 10,000 IU to 9 IU) to be used in the formulation of the film coating. Zones of inhibition were measured after incubation on tryptic soy agar (37 degrees C, 48 h). Low-density polyethylene films coated with differing levels of nisin were characterized by field emission scanning electron microscopy, tensile strength, elongation, and water vapor transmission rate. The MIC of nisin in solution was 157 mg/ml. All acids were equally inhibitory (P > 0.05), but acetic acid produced the largest zone of inhibition (21 mm). Field emission scanning electron microscopy confirmed that the cloudy appearance of the films was due to sodium chloride found in the commercially prepared nisin. Tensile strength increased as nisin concentration increased, which also corresponded to increasing film thickness. The nisin coatings (10,000 and 2,500 IU/ml) did not have a significant effect (P > 0.05) on the water vapor transmission rate of the low-density polyethylene film.

Inhibition of Listeria monocytogenes on the surface of individually packaged hot dogs with a packaging film coating containing nisin.

The objective of this study was to determine the effectiveness of packaging films coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing 10,000, 7,500, 2,500, or 156.3 IU/ml nisin for controlling Listeria monocytogenes on the surfaces of vacuum-packaged hot dogs. Barrier film coated with a methylcellulose/hydroxypropyl methylcellulose-based solution containing nisin or no nisin (control) was heat sealed to form individual pouches. Hot dogs were placed in control and nisin-containing pouches and inoculated with a five-strain L. monocytogenes cocktail (approximately 5 log CFU per package), vacuum sealed, and stored for intervals of 2 h and 7, 15, 21, 28, and 60 d at 4 degrees C. After storage, hot dogs and packages were rinsed with 0.1% peptone water. Diluent was spiral plated on modified oxford agar and tryptic soy agar and incubated to obtain counts (CFU per package). L. monocytogenes counts on hot dogs packaged in films coated with 156.3 IU/ml nisin decreased slightly (approximately 0.5-log reduction) through day 15 of refrigerated storage but was statistically the same (P > 0.05) as hot dogs packaged in films without nisin after 60 d of storage. Packaging films coated with a cellulose-based solution containing 10,000 and 7,500 IU/ml nisin significantly decreased (P < 0.05) L. monocytogenes populations on the surface of hot dogs by greater than 2 log CFU per package throughout the 60-d study. Similar results were observed for hot dogs packaged in films coated with 2,500 IU/ml nisin; however, L. monocytogenes populations were observed to be approximately 4 log CFU per package after 60 d of refrigerated storage from plate counts on tryptic soy and modified oxford agars.

Inbreeding and the genetic variance in floral traits of Mimulus guttatus.

The additive genetic variance, V(A), is frequently used as a measure of evolutionary potential in natural plant populations. Many plants inbreed to some extent; a notable observation given that random mating is essential to the model that predicts evolutionary change from V(A). With inbreeding, V(A) is not the only relevant component of genetic variation. Several nonadditive components emerge from the combined effects of inbreeding and genetic dominance. An important empirical question is whether these components are quantitatively significant. We use maximum likelihood estimation to extract estimates for V(A) and the nonadditive 'inbreeding components' from an experimental study of the wildflower Mimulus guttatus. The inbreeding components contribute significantly to four of five floral traits, including several measures of flower size and stigma-anther separation. These results indicate that inbreeding will substantially alter the evolutionary response to natural selection on floral characters.

Deleterious mutations and genetic variation for flower size in Mimulus guttatus.

Mimulus guttatus is a wildflower that exhibits substantial genetic variation in flower size. Here, we test the hypothesis that this variation is caused by deleterious mutations maintained through mutation-selection balance. The deleterious-mutation model predicts that rare, partially recessive alleles will be the primary source of variation. We test this prediction by measuring the change in the mean flower size (deltaM) and the directional dominance of flower size (deltaB) within a selection experiment. If variation is due to rare (partially) recessive alleles, deltaB/deltaM is expected to be positive and exceed one. However, we obtain negative values for deltaB/deltaM from three independent selection lines. This result is statistically inconsistent with the deleterious-mutation model.