The cost of stress: Dry matter partitioning changes with seasonal supply of water and nitrogen to dryland wheat

Spring wheat cv. ‘Gutha’ was grown in continuous wheat (W/W) and narrow-leafed lupin (L. angustifolius L. cv. Yandee)-wheat (L/W) rotation on a yellow earth over mottled clay (Arenic Fragiudult) in a mediterranean climate for two years. The first year had a higher than average rainfall with adequate soil water until anthesis. The second year was very dry (only 232 mm total rainfall) and soil water contents were low throughout the growing season. Nitrogen fertilizer (+N) treatments were included in both years. In the first year an adjacent experiment compared the effects of loosening a pronounced traffic pan which existed on the site (LS)versus unloosened (US). In the first year roots contained more dry matter than tops in the early vegetative stage in all crops and then declined exponentially to a ratio of 0.1 in the US and LS treatments. In the second year however, the decline was both linear and much less, so that root:shoot ratios at harvest were still between 0.4 and 0.8. There was a consistent trend in root:shoot ratios from the most favourable (LS) to least favourable (W/W-N) treatments over the combined two years’ data, and this was also found in grain yield, with a higher yield in year one from the LS than US, and the lowest yield in year two from the W/W-N treatment. The proportion of total biomass recovered from below ground was substantially higher than is commonly reported from studies carried out in temperate, high fertility soils, but probably still under-estimates of the true amount of dry matter in roots because of inadequacies of sampling, washing and storage techniques. Root length densities were much greater in the drier year, especially in the surface 0.1-m, and based on theoretical considerations, much greater than required for extraction of available water. The effect of environmental conditions on the relative size of cereal crop carbon sinks are discussed in relation to these results.     

Relation of risk of systemic lupus erythematosus to west African admixture in a Caribbean population

Risk of systemic lupus erythematosus (SLE) is higher in people of west African descent than in Europeans. The objective of this study was to distinguish between genetic and environmental explanations for this ethnic difference by examining the relationship of disease risk to individual admixture (defined as the proportion of the genome that is of west African ancestry); 124 cases of SLE and 219 matched controls resident in Trinidad were studied. Analysis of admixture was restricted to 52 cases and 107 controls who reported no Indian or Chinese ancestry. These individuals were typed with a panel of 26 single-nucleotide polymorphisms and five insertion/deletion polymorphisms chosen to have large allele frequency differentials between west African, European and Native American populations. A Bayesian model for population admixture, individual admixture and locus ancestry was fitted by Markov chain simulation. Mean west African admixture (M) was 0.81 in cases and 0.74 in controls (P=0.01). The risk ratio for SLE associated with unit change in M was estimated as 32.5 with a 95% confidence interval (CI) of 2.0-518. Adjustment for measures of socioeconomic status (household amenities in childhood and years of education) altered this risk ratio only slightly (adjusted risk ratio: 28.4, 95% CI 1.7-485). These results support an additive genetic model for the ethnic difference in risk of SLE between west Africans and Europeans, rather than an environmental explanation or an "overdominant" model in which risk is higher in heterozygous than in homozygous individuals. This conclusion lays a basis for localizing the genes underlying this ethnic difference in risk of SLE by admixture mapping.     

A general mechanistic model for admixture histories of hybrid populations

Admixed populations have been used for inferring migrations, detecting natural selection, and finding disease genes. These applications often use a simple statistical model of admixture rather than a modeling perspective that incorporates a more realistic history of the admixture process. Here, we develop a general model of admixture that mechanistically accounts for complex historical admixture processes. We consider two source populations contributing to the ancestry of a hybrid population, potentially with variable contributions across generations. For a random individual in the hybrid population at a given point in time, we study the fraction of genetic admixture originating from a specific one of the source populations by computing its moments as functions of time and of introgression parameters. We show that very different admixture processes can produce identical mean admixture proportions, but that such processes produce different values for the variance of the admixture proportion. When introgression parameters from each source population are constant over time, the long-term limit of the expectation of the admixture proportion depends only on the ratio of the introgression parameters. The variance of admixture decreases quickly over time after the source populations stop contributing to the hybrid population, but remains substantial when the contributions are ongoing. Our approach will facilitate the understanding of admixture mechanisms, illustrating how the moments of the distribution of admixture proportions can be informative about the historical admixture processes contributing to the genetic diversity of hybrid populations.     

Studies on several genetic hematological traits of the Mexican population. XVI. Hemoglobin, S and glucose-6-phosphate dehydrogenase deficiency in the east coast

The distribution of abnormal hemoglobins, glucose-6-phosphate dehydrogenase deficiency, blood group antigens A, B, M, N, C, c, D, E, e, V, Duffy and Diego, serum haptoglobins, transferrins and pseudocholinesterase types, were investigated in five villages of the East Coast of Mexico, where vivax malaria was endemic until recently. Hemoglobin S and G-6-PD deficiency were present in variable degrees in all five locations. All patients with the enzyme deficiency had the A band by electrophoresis, which coupled with the presence of hemoglobin C and haptoglobin 2-1 M in a few individuals strongly suggested Negro admixture. The high frequency of antigen V and the relatively low frequency of Fy (a +) were congruent with the above hypothesis and the conclusion was drawn that the presence of hemoglobin S and G-6-PD deficiency in this area is due to Negro admixture. Unusually high frequencies of the Diego antigen were observed in three of the five villages studied.     

On the genetic interrelationships of South African Negroes

This study addresses the comparative genetic interrelationships between South African Negro groups. For this the genetic distances between seven ethnically defined Negro subsamples (total of 998 individuals) based on 24 genetic loci/polymorphisms are calculated by applying standard distance formulae. These computations offer an opportunity to evaluate the different polymorphisms in terms of their effects on the genetic distances. The genetic interrelationships thus computed are illustrated by way of dendrograms and are discussed in terms of their comparative significance. It follows from the findings that the Ndebele, Northern Sotho (Pedi), and Tswana form a closely related subcluster and that the Zulu and Swazi as well as the Venda and Shangana-Tsonga form two additional, more distant, subclusters. These results are discussed and tentatively interpreted against the background of the reported Khoisan admixture of the populations concerned as well as their ethnological history. The data are also compared to those derived from metric and dermatoglyphic studies. It is concluded that whereas there is some agreement between these categories of variation (genetic, metric, and dermatoglyphic) as far as the comparative evaluation of South African Negro groups is concerned, there also are discrepancies. These conclusions need to be explained in terms of evolutionary mechanisms (such as historic origins, hybridization, natural selection, and genetic drift) in order to obtain a more consistent and comprehensive comparative picture of the physical anthropology of southern African populations.     

Vertical growth of the anterior face and cranium in inner city Negro children

A longitudinal cephalometric study was conducted on the vertical growth of the cranium and anterior face on 60 inner city American Negro children, an equal number of boys and girls from four to nine years. Three vertical measurements were used for the purpose of this study. The head height was measured from sellion to bregma, bony nasal height from nasion to anterior nasal spine, and lower facial height from anterior nasal spine and lower facial height from anterior nasal spine to menton. The data were analyzed at annual ages and observations made relative to the growth trends. The findings of this study were compared with those on Caucasian children. No significant statistical difference was found in the mean head (cranial vault) height between the Negro and Caucasian children. The mean bony nasal height expressed as a percentage of subnasal height was found to be less in the Negro children. The difference decreased with age. The annual increment of growth in head height was greater from four to seven years than from seven to nine years. The findings are considered to imply that severe malnutrition may influence child growth.     

Rapid morphological change in living humans: implications for modern human origins

Human body size and body proportions are interpreted as markers of ethnicity, 'race,' adaptation to temperature, nutritional history and socioeconomic status. Some studies emphasize only one of these indicators and other studies consider combinations of indicators. To better understand the biocultural nature of human size and proportions a new study of the growth of Maya-American youngsters was undertaken in 1999 and 2000. One purpose of this research is to assess changes in body proportion between Maya growing up in the US and Maya growing up in Guatemala. Height and sitting height of 6-12-year-old boys and girls (n=360) were measured and the sitting height ratio [sitting height/height]x100, a measure of proportion, was calculated. These data are compared with a sample of Maya of the same ages living in Guatemala and measured in 1998 (n=1297). Maya-American children are currently 10.24 cm taller, on average, and have a significantly lower sitting height ratio, (i.e. relatively longer legs, averaging 7.02 cm longer) than the Guatemala Maya. Maya-American children have body proportions more like those of white children in the US than like Maya children in Guatemala. Improvements in the environment for growth, in terms of nutrition and health, seem to explain both the trends in greater stature and relatively longer legs for the Maya-Americans. These findings are applied to the problem of modern human origins as assessed from fossil skeletons. It has been proposed that heat adapted, relatively long-legged Homo sapiens from Africa replaced the cold adapted, relatively short-legged Homo neandertalensis of the Levant and Europe [J Hum Evol 32 (1997a) 423]. Skeletal samples of Maya adults from rural Guatemala have body proportions similar to adult Neandertals and to skeletal samples from Europe with evidence of nutritional and disease stress. Just as nutrition and health status explains the differences in the body proportions of living Maya children, these factors, along with adaptation to climate, may also explain much of the differences between the Neandertal and African hominid samples.     

Canadian fertility trends in perspective

This paper examines the broad movements of Canadian period and cohort fertility over the past 100 years, and compares them with corresponding trends in the US and other industrialized countries. The main movement in Canada was a decline in fertility extending from the 19th century to the present, interrupted in the 1940s and 1950s by a baby boom. Between 1871 and 1937 the total fertility rate (TFR) fell at about an average of 1.4% annually. The rate of fall in the US was similar, with the result that in the late 1930s the Canadian TFR was about 20% that of the US. The fertility boom that followed was steeper in the US than in Canada, and in the downswing that later followed, the rate of decline was similar in the 2 countries (3.4-4% annual average). But, the decline continued longer-- indeed still continues--in Canada, whereas the TFR in the US reached its lowest point in 1976. Moreover, the recent decline in fertility has been more severe in Canada than in almost any other industrialized country. The TFR relates to fertility in a single year and is highly sensitive to short-term changes in the timing of births. For the purposes of understanding and explaining long-term trends in fertility, the completed fertility rate (CFR) is a better index because it measures the ultimate family size of cohorts. Cohort fertility can be seen to fluctuate much less than does period fertility. In both the US and Canada, the peak cohorts, born in the early 1930s, had roughly the same completed fertility, and later cohorts continued to remain closely in step as the CFR fell sharply. In Canada the fall continues, though at a reduced rate, in the latest cohorts for which there is information. Apart from differences in amplitude, the dates of turning points and the shapes of the TFR and CFR curves of Canadian fertility are fairly similar. The long decline in cohort fertility is largely explained by the decrease in the proportions of families of 6 or more children. During the baby boom, for Catholics and non-Catholics alike, the proportion of ever-married women remaining childless fell by about 40%, the proportion having 2 children changed little, and the proportions having 3,4 and 5 children tended to increase substantially. The crucial difference between the 2 groups was in the proportions of women having 6 or more children. For non-Catholics, the proportion fell by over 4% from a high level. For non-Catholics, on the other hand, the proportion rose somewhat, though even after the rise, it was barely more than 1/2 the level to which the Catholic proportion had declined. Among Catholics, the effect of the massive decline in the proportion of women having 6 or more children was to swamp the effects of the increase in the proportions of women having 3, 4 and 5 children. The net effect was that fertility declined. Among non-Catholics, however, the comparable increases in the proportions of families of 3, 4 and 5 children, were not offset by any fall in the proportion of larger families, with the result that a baby boom occurred.     

Admixture in Mexico City: implications for admixture mapping of Type 2 diabetes genetic risk factors

Admixture mapping is a recently developed method for identifying genetic risk factors involved in complex traits or diseases showing prevalence differences between major continental groups. Type 2 diabetes (T2D) is at least twice as prevalent in Native American populations as in populations of European ancestry, so admixture mapping is well suited to study the genetic basis of this complex disease. We have characterized the admixture proportions in a sample of 286 unrelated T2D patients and 275 controls from Mexico City and we discuss the implications of the results for admixture mapping studies. Admixture proportions were estimated using 69 autosomal ancestry-informative markers (AIMs). Maternal and paternal contributions were estimated from geographically informative mtDNA and Y-specific polymorphisms. The average proportions of Native American, European and, West African admixture were estimated as 65, 30, and 5%, respectively. The contributions of Native American ancestors to maternal and paternal lineages were estimated as 90 and 40%, respectively. In a logistic model with higher educational status as dependent variable, the odds ratio for higher educational status associated with an increase from 0 to 1 in European admixture proportions was 9.4 (95%, credible interval 3.8–22.6). This association of socioeconomic status with individual admixture proportion shows that genetic stratification in this population is paralleled, and possibly maintained, by socioeconomic stratification. The effective number of generations back to unadmixed ancestors was 6.7 (95% CI 5.7–8.0), from which we can estimate that genome-wide admixture mapping will require typing about 1,400 evenly distributed AIMs to localize genes underlying disease risk between populations of European and Native American ancestry. Sample sizes of about 2,000 cases will be required to detect any locus that contributes an ancestry risk ratio of at least 1.5.     

Investigations on the Physical Structure and the Mechanism of Drug Release from an Enteric Matrix Microspheres with a Near-Zero-Order Release Kinetics Using SEM and Quantitative FTIR

The objectives of this study were to evaluate the physical structure and the release mechanisms of theophylline microspheres made of Eudragit S 100 polymer as an enteric polymer, combined with a nonerodible polymer, Eudragit RL 100. In the preparation process, polymer combinations (1:1) were dissolved in an organic solvent mixture composed of acetone and methanol at a specific ratio containing a theoretical drug loading of approximately 15%. Two microsphere formulations (LS1 and LS2) were prepared at two different total polymer concentrations (10% in LS1 and 12.7% in LS2). Dissolution studies were carried out using US Pharmacopeia Dissolution Apparatus II in an acidic medium for 8 h and in an acidic medium (2 h) followed by a slightly basic-buffered medium for 10 h. Both LS1 and LS2 microsphere formulations produced particles that were spherical in shape and had very narrow size distributions with one size fraction comprising 70–80% of the yield. Scanning electron microscopy and quantitative Fourier transform infrared were used for microsphere physical structure evaluation. Except for the absence of drug crystals, photomicrographs of both LS microspheres after dissolution in pH 1.2 and 7.2 buffer solutions were similar to those before dissolution. Dissolution results indicated the ability of LS microspheres to minimize drug release during the acid stage. However, in the slightly basic medium that followed the acidic stage, the drug release was sustained and controlled in its kinetics and data fitted to Peppas equation indicated a case II transport suggesting that the drug release is mainly through swelling/erosion mechanism.     

Economic impact on tooth emergence

As shown in nearly 10,000 Negro and White boys and girls between 4.5 and 16.5 years of age, poverty-level children (with an income-to-needs ratio of 1.0) tend to be delayed in permanent tooth emergence as compared with those approximating median per-capita income. For boys, a per-capita income difference of $2200 was associated with a 0.15 standard deviation difference in emergence timiing of 28 permanent teeth.     

Fingerprints of Whites and Negroes from Southern Brazil

Studies on 1,115 individuals (451 Whites, 240 Light Mulattoes, 236 Dark Mulattoes and 188 Negroes) from Pôrto Alegre, Brazil are reported. The differences among those subgroups are not large and there is not a clear gradient when we consider samples with increasing Negro ancestry. The most marked difference between Whites and the total Negroid group occurred in the prevalence of radial loops. Comparison with Portuguese and African series indicates that no single factor can fully explain the observed distributions. But the values of Dankmeijer's index are exactly those expected on the assumption of 50% White admixture in the Pôrto Alegre Negro, in agreement with previous investigations.     

Height and weight growth patterns of school age deaf children

Distance and velocity curves for height and weight were analyzed in a mixed longitudinal sample of American White, American Negro and Mexican-American deaf children 6 through 17 years of age. The heights of deaf boys and girls are, on the average, consistently below an accepted pediatric standard from six through ten years of age. Between 11 and 17 years, deaf White and Negro boys approximate the standard, while White and Negro girls are at or slightly below the standard. Deaf Mexican-American children are consistently below the height standard. For body weight, deaf boys are at or slightly below the standard from 6 to 11 years, and are at or slightly above the weight standard from 12 to 17 years of age. White and Negro deaf girls generally approximate the weight standard from eight years of age on. Mexican-American deaf girls are consistently below the standard until 13 years of age, while between 14 and 17 years they are at or above the standard. Height and weight velocity curves for deaf children parallel closely the incremental standards of Falkner ('62). The height velocity curve, however, appears to peak, on the average, about one year earlier in deaf children.     

Studies on several genetic hematological traits of the Mexican population. XII. Distribution of blood group antigens in twelve Indian tribes

Blood samples from 1090 Mexican Indians belonging to the Chol, Chontal, Totonac, Huastec, Mixe, Mazatec, Zapotec, Mixtec, Chinantec, Nahua, Cora and Huichol linguistic groups, were obtained and examined in regard to the following blood group antigens: A, B. M, N, P, C, c, D, E, e, Fy(a), K and Di(a). The gene frequencies were similar to what has been described for other Amerindians; high values for O, M, CDe, cDE and Duffy; low to absent Kell and presence of Diego in variable amounts. The frequency of chromosomes CDE and cDe/cde was somewhat higher than usual and some of the tribes had relatively high frequencies of the A and B antigens. It was felt that variable degrees of non-Indian admixture was at least partially responsible for this situation. A previous study dealing with the distribution of abnormal hemoglobins and glucose-6-phosphate dehydrogenase deficiency in these same tribes, had strongly suggested the possibility of some Negro admixture in the Chontal, Nahua and Cora tribes. However, this was not specifically reflected in their blood group distribution. This served to emphasize the need of investigating as many markers as possible when trying to characterize a population.     

Notches in the non-epiphyseal ends of the metacarpals and phalanges in children of four South African populations

The incidence of notches in the non-epiphyseal ends of the shafts of the metacarpals and phalanges was determined from radiographs of the left hand of 1,303 Pretoria school-children aged 6 to 11 years. The group included White, Negro, Coloured and Indian children. The notches represent vestiges of supernumerary epiphyses or pseudo-epiphyses. Notching of one or more of the metacarpals or phalanges was found in 88.9% of White children, 77.1% of Negro children, 84.3% of Coloured children and 78.8% of Indian children. Notches were most common in metacarpal I followed in declining order of frequency by metacarpal II, metacarpal V, middle phalanx V and proximal phalanx I. Notches were rare in other sites. The mean number of notches per subject was significantly higher in males than in females in all four population groups. However, the sex differences appear to be due mainly to earlier obliteration of notches in females. The findings in White children suggest that there is no significant relationship between metacarpal and phalangeal notching and skeletal maturation rate. Notches are significantly more common in Pretoria Whites than in relatively poorly nourished Pretoria Negro children. It is concluded that the occurrence of notches is a normal phenomenon accompanying the ossification of the hand skeleton and that notching is related neither to retardation in skeletal development nor to undernutrition.     

Analysis of admixture and genetic structure of two Native American groups of Southern Argentinean Patagonia

Argentinean Patagonia is inhabited by people that live principally in urban areas and by small isolated groups of individuals that belong to indigenous aboriginal groups; this territory exhibits the lowest population density of the country. Mapuche and Tehuelche (Mapudungun linguistic branch), are the only extant Native American groups that inhabit the Argentinean Patagonian provinces of Río Negro and Chubut. Fifteen autosomal STRs, 17 Y-STRs, mtDNA full length control region sequence and two sets of Y and mtDNA-coding region SNPs were analyzed in a set of 434 unrelated individuals. The sample set included two aboriginal groups, a group of individuals whose family name included Native American linguistic root and urban samples from Chubut, Río Negro and Buenos Aires provinces of Argentina. Specific Y Amerindian haplogroup Q1 was found in 87.5 % in Mapuche and 58.82 % in Tehuelche, while the Amerindian mtDNA haplogroups were present in all the aboriginal sample contributors investigated. Admixture analysis performed by means of autosomal and Y-STRs showed the highest degree of admixture in individuals carrying Mapuche surnames, followed by urban populations, and finally by isolated Native American populations as less degree of admixture. The study provided novel genetic information about the Mapuche and Tehuelche people and allowed us to establish a genetic correlation among individuals with Mapudungun surnames that demonstrates not only a linguistic but also a genetic relationship to the isolated aboriginal communities, representing a suitable proxy indicator for assessing genealogical background.     

Comparing genetic ancestry and self-reported race/ethnicity in a multiethnic population in New York City

Self-reported race/ethnicity is frequently used in epidemiological studies to assess an individual’s background origin. However, in admixed populations such as Hispanic, self-reported race/ethnicity may not accurately represent them genetically because they are admixed with European, African and Native American ancestry. We estimated the proportions of genetic admixture in an ethnically diverse population of 396 mothers and 188 of their children with 35 ancestry informative markers (AIMs) using the STRUCTURE version 2.2 program. The majority of the markers showed significant deviation from Hardy-Weinberg equilibrium in our study population. In mothers self-identified as Black and White, the imputed ancestry proportions were 77.6% African and 75.1% European respectively, while the racial composition among self-identified Hispanics was 29.2% European, 26.0% African, and 44.8% Native American. We also investigated the utility of AIMs by showing the improved fitness of models in paraoxanase-1 genotype-phenotype associations after incorporating AIMs; however, the improvement was moderate at best. In summary, a minimal set of 35 AIMs is sufficient to detect population stratification and estimate the proportion of individual genetic admixture; however, the utility of these markers remains questionable.     

Mapping genes that underlie ethnic differences in disease risk: methods for detecting linkage in admixed populations, by conditioning on parental admixture.

Genes that underlie ethnic differences in disease risk can be mapped in affected individuals of mixed descent if the ancestry of the alleles at each marker locus can be assigned to one of the two founding populations. Linkage can be detected by testing for association of the disease with the ancestry of alleles at the marker locus, by conditioning on the admixture (defined as the proportion of genes that have ancestry from the high-risk population) of both parents. With regard to exploiting the effects of admixture, this test is more flexible and powerful than the transmission-disequilibrium test. Under the assumption of a multiplicative model, the statistical power for a given sample size depends only on parental admixture and the risk ratio r between populations that is generated by the locus. The most informative families are those in which mean parental admixture is .2-.7 and in which admixture is similar in both parents. The number of markers required for a genome search depends on the number of generations since admixture and on the information content for ancestry (f) of the markers, defined as a function of allele frequencies in the two founding populations. Simulations using a hidden Markov model suggest that, when admixture has occurred 2-10 generations earlier, a multipoint analysis using 2,000 biallelic markers, with f values of 30%, can extract 70%-90% of the ancestry information for each locus. Sets of such markers could be selected from libraries of single-nucleotide polymorphisms, when these become available.     

The dermatoglyphic characteristics of two isolated Bedouin groups from South Sinai

The dermatoglyphics of the Muzeina and Gebeliya Bedouin tribes, two small biologically isolated populations, leading a similar nomadic life under the specific conditions of the Sinai desert, were studied. The differences found between the studied samples concern particularly the frequencies of palmar and finger pattern types. These differences are in agreement with data on the origin of the tribes, a Negro and/or European admixture being evident in the Gebeliya dermatoglyphics. The coefficients of variation for some quantitative dermatoglyphic traits, presumably with a polygenic determination, are lower in the Muzeina than in the Gebeliya sample. Isolation and consanguinity may exert their influence on the dermatoglyphic traits influencing the frequencies of the corresponding genes.