Between-line Differences Research Articles

Mutations in a Novel Cadherin Gene Associated with Bt Resistance in Helicoverpa zea.

Transgenic corn and cotton produce crystalline (Cry) proteins derived from the soil bacterium Bacillus thuringiensis (Bt) that are toxic to lepidopteran larvae. Helicoverpa zea, a key pest of corn and cotton in the U.S., has evolved widespread resistance to these proteins produced in Bt corn and cotton. While the genomic targets of Cry selection and the mutations that produce resistant phenotypes are known in other lepidopteran species, little is known about how selection by Cry proteins shape the genome of H. zea. We scanned the genomes of Cry1Ac-selected and unselected H. zea lines, and identified twelve genes on five scaffolds that differed between lines, including cadherin-86C (cad-86C), a gene from a family that is involved in Cry1A resistance in other lepidopterans. Although this gene was expressed in the H. zea larval midgut, the protein it encodes has only 17 to 22% identity with cadherin proteins from other species previously reported to be involved in Bt resistance. An analysis of midgut-expressed cDNAs showed significant between-line differences in the frequencies of putative nonsynonymous substitutions (both SNPs and indels). Our results indicate that cad-86C is a likely target of Cry1Ac selection in H. zea. It remains unclear, however, whether genomic changes at this locus directly disrupt midgut binding of Cry1Ac and cause Bt resistance, or indirectly enhance fitness of H. zea in the presence of Cry1Ac by some other mechanism. Future work should investigate phenotypic effects of these nonsynonymous substitutions and their impact on fitness of H. zea larvae that ingest Cry1Ac.

Functional and structural changes in aorta of mice divergently selected for basal metabolic rate

Cardiovascular diseases (CVD) are one of the most common causes of mortality likely genetically linked to the variation in basal metabolic rate (BMR). A robust test of the significance of such association may be provided by artificial selection experiments on animals selected for diversification of BMR. Here we asked whether genetically determined differences in BMR correlate with anatomical shift in endothelium structure and if so, the relaxation and contraction responses of the aorta in mice from two lines of Swiss-Webster laboratory mice (Mus musculus) divergently selected for high or low BMR (HBMR and LBMR lines, respectively). Functional and structural study of aorta showed that a selection for divergent BMR resulted in the between-line difference in diastolic aortic capacity. The relaxation was stronger in aorta of the HBMR mice, which may stem from greater flexibility of aorta mediated by higher activity of Ca2+-activated K+ channels. Structural examination also indicated that HBMR mice had significantly thicker aorta's middle layer compared to LBMR animals. Such changes may promote arterial stiffness predisposing to cardiovascular diseases. BMR-related differences in the structure and relaxation ability of aortas in studied animals may be reminiscent of potential risk factors in the development of CVD in humans.

Effect of calorie restriction on spontaneous physical activity and body mass in mice divergently selected for basal metabolic rate (BMR)

Spontaneous physical activity (SPA) represents an important component of daily energy expenditures in animals and humans. Intra-specific variation in SPA may be related to the susceptibility to metabolic disease or obesity. In particular, reduced SPA under conditions of limited food availability may conserve energy and prevent loss of body and fat mass (‘thrifty genotype hypothesis’). However, both SPA and its changes during food restriction show wide inter-individual variations. We studied the effect of 30% caloric restriction (CR) on SPA in laboratory mice divergently selected for high (H-BMR) and low (L-BMR) basal metabolic rate. Selection increased SPA in the H-BMR line but did not change it in the L-BMR mice. This effect reflected changes in SPA intensity but not SPA duration. CR increased SPA intensity more strongly in the L-BMR line than in the H-BMR line and significantly modified the temporal variation of SPA. However, the initial between-line differences in SPA were not affected by CR. Loss of body mass during CR did not differ between both lines. Our results show that the H-BMR mice can maintain their genetically determined high SPA under conditions of reduced food intake without sacrificing their body mass. We hypothesize that this pattern may reflect the higher flexibility in the energy budget in the H-BMR line, as we showed previously that mice from this line reduced their BMR during CR. These energy savings may allow for the maintenance of elevated SPA in spite of reduced food intake. We conclude that the effect of CR on SPA is in large part determined by the initial level of BMR, whose variation may account for the lack of universal pattern of behavioural responses to CR.

Reduced CYFIP1 in Human Neural Progenitors Results in Dysregulation of Schizophrenia and Epilepsy Gene Networks

Deletions encompassing the BP1-2 region at 15q11.2 increase schizophrenia and epilepsy risk, but only some carriers have either disorder. To investigate the role of CYFIP1, a gene within the region, we performed knockdown experiments in human neural progenitors derived from donors with 2 copies of each gene at the BP1-2 locus. RNA-seq and cellular assays determined that knockdown of CYFIP1 compromised cytoskeletal remodeling. FMRP targets and postsynaptic density genes, each implicated in schizophrenia, were significantly overrepresented among differentially expressed genes (DEGs). Schizophrenia and/or epilepsy genes, but not those associated with randomly selected disorders, were likewise significantly overrepresented. Mirroring the variable expressivity seen in deletion carriers, marked between-line differences were observed for dysregulation of disease genes. Finally, a subset of DEGs showed a striking similarity to known epilepsy genes and represents novel disease candidates. Results support a role for CYFIP1 in disease and demonstrate that disease-related biological signatures are apparent prior to neuronal differentiation.

Predicting heterosis for egg production traits in crossbred offspring of individual White Leghorn sires using genome-wide SNP data.

BackgroundThe development of a reliable method to predict heterosis would greatly improve the efficiency of commercial crossbreeding schemes. Extending heterosis prediction from the line level to the individual sire level would take advantage of variation between sires from the same pure line, and further increase the use of heterosis in crossbreeding schemes. We aimed at deriving the theoretical expectation for heterosis due to dominance in the crossbred offspring of individual sires, and investigating how much extra variance in heterosis can be explained by predicting heterosis at the individual sire level rather than at the line level. We used 53 421 SNP (single nucleotide polymorphism) genotypes of 3427 White Leghorn sires, allele frequencies of six White Leghorn dam-lines and cage-based records on egg number and egg weight of ~210 000 crossbred hens.ResultsWe derived the expected heterosis for the offspring of individual sires as the between- and within-line genome-wide heterozygosity excess in the offspring of a sire relative to the mean heterozygosity of the pure lines. Next, we predicted heterosis by regressing offspring performance on the heterozygosity excess. Predicted heterosis ranged from 7.6 to 16.7 for egg number, and from 1.1 to 2.3 grams for egg weight. Between-line differences accounted for 99.0% of the total variance in predicted heterosis, while within-line differences among sires accounted for 0.7%.ConclusionsWe show that it is possible to predict heterosis at the sire level, thus to distinguish between sires within the same pure line with offspring that show different levels of heterosis. However, based on our data, variation in genome-wide predicted heterosis between sires from the same pure line was small; most differences were observed between lines. We hypothesise that this method may work better if predictions are based on SNPs with identified dominance effects.

Mice divergently selected for high and low basal metabolic rates evolved different cell size and organ mass

Evolution of metabolic rates of multicellular organisms is hypothesized to reflect the evolution of their cell architecture. This is likely to stem from a tight link between the sizes of cells and nuclei, which are expected to be inversely related to cell metabolism. Here, we analysed basal metabolic rate (BMR), internal organ masses and the cell/nucleus size in different tissues of laboratory mice divergently selected for high/low mass-corrected BMR and four random-bred mouse lines. Random-bred lines had intermediate levels of BMR as compared to low- and high-BMR lines. Yet, this pattern was only partly consistent with the between-line differences in cell/nucleus sizes. Erythrocytes and skin epithelium cells were smaller in the high-BMR line than in other lines, but the cells of low-BMR and random-bred mice were similar in size. On the other hand, the size of hepatocytes, kidney proximal tubule cells and duodenum enterocytes were larger in high-BMR mice than other lines. All cell and nucleus sizes were positively correlated, which supports the role of the nucleus in cell size regulation. Our results suggest that the evolution of high BMR involves a reduction in cell size in specialized tissues, whose functions are primarily dictated by surface-to-volume ratios, such as erythrocytes. High BMR may, however, also incur an increase in cell size in tissues with an intense transcription and translation, such as hepatocytes.

Milk output and composition in mice divergently selected for basal metabolic rate.

From an evolutionary perspective, the high basal metabolic rate (BMR) of homeotherms is hypothesised to be a by-product of natural selection for effective parental care. We estimated daily milk output during two consecutive lactation bouts in mice divergently selected for high/low BMR and applied a cross-fostered design to control for potential differences in the between-line suckling abilities of nursed juveniles. Additionally, to remedy the potential limitation imposed by the ability of mother mice to dissipate excess heat, we exposed them to an ambient temperature of 17°C during the most energetically demanding second week of lactation. We found that the mice selected for high BMR produced significantly more milk in a 24 h period in both reproductive bouts. The milk samples obtained from the high BMR females had lower protein concentration and did not differ with respect to fat. However, the concentration of the primary milk carbohydrate – lactose – was higher. Although all the above between-line differences were statistically significant, their magnitude was too small to unambiguously ascribe them as stemming from a positive genetic correlation between the physiological traits underlying BMR and lactation performance. Nevertheless, our study lends such support at least at the level of phenotypic variation.

Genetic variation of contact dermatitis in broilers

This study aimed to investigate the presence of genetic variation in footpad dermatitis (FPD) and hock burns (HB) and the possibility to genetically select against these. A field trial including 10 commercial broiler lines (n = 102 to 265) was carried out at 2 Dutch farms. Footpad dermatitis and HB were subjectively scored at approximately 4, 5, and 7 wk on a scale from 0 through 5. Genetic parameters were estimated in 2 lines based on a larger data set. The overall agreement of repeated FPD and HB scores was high (0.66 to 0.86) and the scoring system was, therefore, considered reliable. Kendall's tau between left and right scores was lower than 1 (FPD: 0.73 and HB: 0.57), and both left and right FPD and HB must, therefore, be evaluated. High prevalences of FPD, but also HB, were achieved in the field trial, but lower prevalences may be sufficient for genetic evaluations and would be less detrimental to welfare. Genetic variation between and within lines was present for both FPD and HB as indicated by between-line differences and heritabilities, and selection against FPD and HB is, therefore, possible. It is important that selection is done against both FPD and HB, and such selection should not have a negative influence on the genetic improvement in BW. In contrast, continued selection for increased BW while ignoring FPD in the breeding goal is likely to lead to an increased propensity to develop FPD in broilers.

The genetic control of chromosome segregation in Drosophila melanogaster

High resp. low frequencies of nondisjunction of the X chromosomes in Drosophila melanogaster were selected for. The base population had been synthesized from four isostructural strains previously used by VALENTIN in a recombination selection experiment. Significant responses were obtained for XXY exceptions in the high line and for X0 exceptions in both lines. The resulting between-line difference can be observed both in male and in female meiosis. Neither line appears to have reduced recombination in X. These observations indicate that the between-line difference is not caused by effects on synapsis but by effects on segregation itself.

Diverse Sensitivity of RHA/Verh and RLA/Verh Rats to Emotional and Spatial Aspects of a Novel Environment as a Result of a Distinct Pattern of Neuronal Activation in the Fear/Anxiety Circuit

Psychogenetically selected Roman high (RHA/Verh) and Roman low (RLA/Verh) avoidance rats constitute a well-recognized model of diverse emotional reactivity. The two Swiss lines display marked behavioral and endocrine differences in reaction to a novel environment. In our study we found that these differences are accompanied by a distinct, line-specific pattern of neuronal activation within the fear/anxiety circuit. We have compared the c-Fos protein expression in the medial prefrontal cortex (mPFC), basolateral (BLA), central (CeA), medial (MeA), and cortical (CoA) nuclei of amygdala, paraventricular nucleus of the hypothalamus (PVN), and CA1, CA2, and CA3 fields of the hippocampus upon exposure to a novel situation of different stressorgeneity (open field with illuminated center, elevated plus maze, hole board test and acute restraint). Profound between-line differences in the sensitivity to emotional and spatial aspects of the behavioral challenge were observed for tests measuring spontaneous behavior. This effect seems to reflect different motivational factors driving the rat behavior, which clearly suggests that the diverse emotional reactivity of RHA/Verh and RLA/Verh rats is a result of different activation of the fear/anxiety circuit.

Computer assisted video analysis of swimming performance in a forced swim test: Simultaneous assessment of duration of immobility and swimming style in mice selected for high and low swim-stress induced analgesia

In behavioral pharmacology, two problems are encountered when quantifying animal behavior: 1) reproducibility of the results across laboratories, especially in the case of manual scoring of animal behavior; 2) presence of different behavioral idiosyncrasies, common in genetically different animals, that mask or mimic the effects of the experimental treatments. This study aimed to develop an automated method enabling simultaneous assessment of the duration of immobility in mice and the depth of body submersion during swimming by means of computer assisted video analysis system (EthoVision from Noldus). We tested and compared parameters of immobility based either on the speed of an object (animal) movement or based on the percentage change in the object's area between the consecutive video frames. We also examined the effects of an erosion–dilation filtering procedure on the results obtained with both parameters of immobility. Finally, we proposed an automated method enabling assessment of depth of body submersion that reflects swimming performance. It was found that both parameters of immobility were sensitive to the effect of an antidepressant, desipramine, and that they yielded similar results when applied to mice that are good swimmers. The speed parameter was, however, more sensitive and more reliable because it depended less on random noise of the video image. Also, it was established that applying the erosion–dilation filtering procedure increased the reliability of both parameters of immobility. In case of mice that were poor swimmers, the assessed duration of immobility differed depending on a chosen parameter, thus resulting in the presence or lack of differences between two lines of mice that differed in swimming performance. These results substantiate the need for assessing swimming performance when the duration of immobility in the FST is compared in lines that differ in their swimming “styles”. Testing swimming performance can also be important in the studies investigating the effects of swim stress on other behavioral or physiological parameters because poor swimming abilities displayed by some lines can increase severity of swim stress, masking the between-line differences or the main treatment effects.

National Pork Producers Council Maternal Line National Genetic Evaluation Program: A comparison of sow longevity and trait associations with sow longevity1

Data from the National Pork Producers Council Maternal Line National Genetic Evaluation Program were used to compare longevity of sows from 6 commercial genetic lines and to estimate the phenotypic associations of sow longevity with gilt backfat thickness, ADG, age at first farrowing, litter size at first farrowing, litter weight at first farrowing, average feed intake during lactation, and average backfat loss during lactation. The lines evaluated were American Diamond Genetics, Danbred North America, Dekalb-Monsanto DK44, Dekalb-Monsanto GPK347, Newsham Hybrids, and National Swine Registry. The data set contained information from 3,251 gilts, of which 17% had censored longevity records (sows lived longer than 6 parities). The line comparison was carried out by analyzing all lines simultaneously. Because the survival distribution functions differed among genetic lines, later analyses were carried out separately for each genetic line. All analyses were based on the non-parametric proportional hazard (Cox model). Dekalb-Monsanto GPK347 sows had a lower risk of being culled than sows from the other lines. Moreover, the shape of the survival distribution function of the Delkab-Monsanto GPK347 line was different from the other 5 lines. The Dekalb-Monsanto 347 line had lower culling rates because they had lower gilt reproductive failure before the first parity than gilts from the other lines. Within line, sows with lower feed intake and greater backfat loss during lactation had a shorter productive lifetime. Thus, producers should implement management practices having positive effects on sow lactation feed intake. Additionally, the swine genetics industry is challenged to simultaneously improve efficiency of gain of their terminal market pigs and to obtain high feed intake during lactation of their maternal lines for future improvement of sow longevity. Recording sow feed intake and backfat loss during lactation in nucleus and multiplication breeding herds should be considered. Between-line differences in this study indicate that it is possible to select for sow longevity, but more research is needed to determine the most efficient selection methods to improve sow longevity.

Daily variation of thermoregulatory costs in laboratory mice selected for high and low basal metabolic rate

Abstract Most mammals are known to have clear circadian rhythms of body temperature ( T b ) and metabolic rate. Large parts of the rhythms correspond to the oscillation of nonshivering thermogenesis (NST), dependent on visceral organ mass, and, affected by mass of brown adipose tissue (BAT). I tested whether: (1) a different levels of BMR result in respective changes of T b values and the magnitude of daily RMR oscillations both within and below thermoneutrality; (2) the amplitude of daily variation of RMR depends on ambient temperature ( T a ). I studied: (1) daily variation of body temperature at T a of 23 °C, and (2) the rate of resting metabolism (RMR) within and below thermoneutrality at the time of minimum and increasing T b (minimum and maximum NST capacity), in two lines of laboratory mice subjected to divergent, artificial selection toward high (HBMR) and low (LBMR) basal rate of metabolism (BMR). All mice had a clear circadian rhythm of T b with minimum of 36.4±0.2 °C at 7:00 and maximum of 37.8±0.2 °C at 21:00. Their RMR measured below thermoneutrality exhibited significant daily variation, with the maximum between 16:00 and 19:00, when T b was rising. Within thermoneutral zone (TNZ) I found between-line, but not between-time, differences in RMR. All between-line differences in RMR could be explained by the magnitude of BMR. I did not find any between-line differences of RMR value in temperatures below thermoneutrality. The amplitude of daily variation of RMR measured below TNZ depended neither on the T a value nor on level of BMR (or visceral organs).

Anatomic and Energetic Correlates of Divergent Selection for Basal Metabolic Rate in Laboratory Mice

The aerobic capacity model postulates that high basal metabolic rates (BMR) associated with endothermy evolved as a correlated response to the selection on maximum, peak metabolic rate Vo2max. Furthermore, the model assumes that BMR and Vo2max are causally linked, and therefore, evolutionary changes in their levels cannot occur independently. To test this, we compared metabolic and anatomical correlates of selection for high and low body mass-corrected BMR in males of laboratory mice of F18 and F19 selected generations. Divergent selection resulted in between-line difference in BMR equivalent to 2.3 phenotypic standard deviation units. Vo2max elicited by forced swimming in 20 degrees C water was higher in the low BMR than high BMR line and did not differ between the lines when elicited by exposure to heliox at -2.5 degrees C. Moreover, the magnitude of swim- and heliox-induced hypothermia was significantly smaller in low BMR mice, whereas their interscapular brown adipose tissue was larger than in high BMR mice. Our results are therefore at variance with the predictions of aerobic capacity model. The selection also resulted in correlated response in food consumption (C) and masses of metabolically active internal organs: kidneys, liver, small intestine, and heart, which fuel maximum, sustained metabolic rate (SusMR) rather than Vo2max. These correlated responses were strong enough to claim the existence of positive, genetic correlations between BMR and the mass of viscera as well as C. Thus, our findings support the suggestion that BMR evolved as a correlated response to selection for SusMR, not Vo2max. In functional terms BMR should therefore be interpreted as a measure of energetic costs of maintenance of metabolic machinery necessary to sustain high levels of energy assimilation rate.

Proteomics and Alcoholism

Publisher Summary This chapter discusses the role of proteomics in alcoholism. Challenges in the alcohol research community continue to focus on how alcohol modifies the brain structure and function differently in individuals at risk for developing alcohol dependence versus those individuals at low or no risk. The use of animal models of alcoholism has been of paramount importance for providing insight into the neurochemical and cellular changes associated with alcohol use and abuse. Several rodent models of alcoholism are used, and the extended amygdala and associated central nervous system (CNS) regions have been implicated in mediating alcohol-reward, and alcohol-seeking behaviors. 2D gel-based experimentation remains an exceptional approach for assessing differential protein expression. It not only enables to separate, detect, and quantify the proteins, but it is also a preparative technique. Proteomic analysis using 2DE separation, and relative quantitation followed by MALDI-TOF MS-identification of relevant protein spots in alcohol-preferring (P) and alcohol-nonpreferring (NP) lines of rat hippocampus and nucleus accumbens demonstrates subtle but significant between-line differences in basal protein expression. However, the more substantive, anticipated differences between them may be masked by limitations of the current proteomics approach.

Correcting Drift Errors in HEM Data

Much HEM survey data suffers from low (spatial) frequency along-line variability in amplitude caused by slow changes in the system geometry and electronic drift. Even though the system is periodically taken up to a sufficient altitude to re-zero the primary field correction, the errors are not totally removed. This paper describes a procedure to reduce the effect of these errors. Each flight line is corrected by subtracting a slowly varying function of time that has been chosen so that the between-line differences over the whole survey area are minimized. The parameters of the correction functions are estimated using weighted, damped least squares. The procedure produces a marked improvement in the quality of the images of low frequency, in-phase channels that have been corrupted by drift noise.

Transgenic expression of a delta 12-epoxygenase gene in Arabidopsis seeds inhibits accumulation of linoleic acid.

The Crepis palaestina cDNA Cpal2 encodes a delta 12-epoxygenase that can catalyse the synthesis of 12,13-epoxy-cis-9-octadecenoic acid (18:1E) from linoleic acid (18:2). When the Cpal2 gene was expressed under the control of the napin seed-specific promoter in Arabidopsis thaliana (L.) Heynh., the seed lipids accumulated only low levels of 18:1E and also 12,13-epoxy-cis-9,15-octadec-2-enoic acid (18:2E). Despite the fact that the levels of these epoxy fatty acids comprised only up to 6.2% of the total fatty acids, there was a very marked increase in oleic acid (18:1) and decrease in linoleic (18:2) and alpha-linolenic (18:3) acids in these plants, indicating that endogenous delta 12-desaturation was greatly reduced in these plants. Significant between-line differences in the levels of Cpal2 mRNA were observed during seed development, but were not associated with any major variation in mRNA levels for the endogenous Arabidopsis delta 12-desaturase (Fad2). This suggests that if an unfavourable interaction occurs between the transgenic delta 12-epoxygenase and the endogenous delta 12-desaturase, which decreases the level of desaturation, it occurs at either the translational or post-translational level. We further show that the co-expression of a delta 12-desaturase gene from C. palaestina in Cpal2 transgenic Arabidopsis returns the relative proportions of the C18 seed fatty acids to normal levels and results in an almost twofold increase in total epoxy fatty acids.

Antibody Responses of Hens Fed Vitamin E and Passively Acquired Antibodies of Their Chicks

Antibody responses of hens and their progeny were studied in commercial broiler nuclear lines. Starting at 168 days of age, individually housed pullets from lines A and B were fed a 16% crude protein and 2752 kcal metabolizable energy/kg mash diet supplemented with either 10 or 300 IU/kg of vitamin E fed as dl-alpha-tocopherol acetate. Fifty-eight days later (226 days of age), 12 hens per line-vitamin E subclass were inoculated i.v. with 0.1 ml of a 2.5% suspension of sheep red blood cells (SRBC). Plasma antibody titers were measured 6, 20, 40, 54, 70, and 88 days after inoculation. Hens from both lines were artificially mated to males from line C, and progeny from eggs collected 9-15, 25-30, and 65-70 days after inoculation were tested for antibodies to SRBC. Hens were reinoculated i.v. with 0.1 ml of 0.25% SRBC 88 days after the first inoculation, and their antibody levels were measured 3, 6, and 20 days later. Eggs laid 10-13 days after reinoculation were incubated, and antibody titers of chicks were measured at hatch. Antibody response of hens to an initial inoculation of SRBC was line-diet-time after inoculation specific. In line A, titers were greater for hens fed the lower than the higher vitamin E diet, whereas diet had no effect on the antibody levels in line B. Line effects (A > B) were observed on days 6 and 20 after inoculation but not thereafter. After the second inoculation, dietary vitamin E level had no effect on antibody levels of hens within lines, whereas a between-line difference (A > B) was observed for the lower but not the higher level of dietary vitamin E. Although there was no difference between diets for antibody transferred to progeny by line B, there was a difference (lower > higher) for line A. After reinoculation of their dams, antibody titers of chicks from line A, but not line B, reached levels similar to those after the first inoculation. Antibody levels were higher for chicks at hatch than in 16-day embryos or 10 days posthatch. The results of this research suggest genetic variation in response to immune stimulation by dietary vitamin E.

Destabilizing Effect of Chicken Selection for the Functional Adrenal Reserves

Chicken lines produced by divergent selection for the functional adrenal reserves showed significant between-line differences in the content of corticosterone and other hormones (thyroxin, progesterone), as well as in body weight, early maturation, and egg yield. DNA fingerprinting with the pGB725 probe revealed molecular changes in genomic DNA of the chicken lines subjected to plus and minus selection. The genetic distances between the original population and the selected chicken lines, which were estimated from the molecular hybridization patterns, reflected the history of breeding. Analysis of mixed DNA from several individuals of each line revealed specific hybridization bands that could serve as DNA markers during selection for the high and low corticosterone levels in blood.

Field Performance and Molecular Evaluations of Pecan Trees Regenerated from Somatic Embryogenic Cultures

Field evaluations were conducted of pecan [Carya illinoinensis (Wangenh.) C. Koch] trees regenerated via somatic embryogenesis to assess if the trees maintained clonal fidelity and exhibited true-to-type characteristics. Phenotypic and molecular comparisons were made of trees from two different tissue culture lines after 4 years in the field. Factors evaluated included shoot growth, leaf morphology, and susceptibility to fungal scab [Cladosporium caryigenum (Ellis & Langl.) Gottwald] and southern pecan leaf phylloxera (Phylloxera russellae Stoetzel). Genetic fidelity was examined using amplified fragment length polymorphism (AFLP) analysis. Statistically significant differences were observed between the culture lines in phenotypic leaf characteristics (i.e., specific leaf weight and leaf length-to-width ratio), number of shoots per 1-year-old branch, and in the frequency of scab lesions on leaves. No between-line differences were observed in trunk caliper, average and total shoot growth, shoot length per cross-sectional area, or presence of phylloxera galls. AFLP analysis readily detected differences between culture lines. Cluster analysis generally grouped trees together that were regenerated from the same line. Trees within a culture line usually exhibited similar leaf characteristics, but not shoot growth or tree height. A few trees exhibited more extreme leaf characteristics and differed from each other. However, they were statistically similar to most of the other trees in the population evaluated. AFLP data revealed that some trees exhibited greater divergence and less similarity than other trees from the same line. The nature and significance of such variation at this time are not related to any detectable phenotypic differences.