The genetic conditions in heterozygous and homozygous populations of Drosophila. II. X-ray induced lethals in a homozygous and a heterozygous population

Strains of Drosophila melanogaster were made isogenic for their second chromosomes by means of the marker strain LCy/Pm. One of these strains was used as a founder for a homozygous experimental population (W). All other strains were mixed and established a heterozygous population (LKW). Both populations were free of lethals in the beginning with respect to their second chromosomes. After they had been exposed to an X-ray irradiation of 7000 r they contained about 26 per cent newly induced lethal chromosomes. Whereas in the heterozygous population the lethal frequency decreased rather fast to 10 per cent, that of the homozygous population remained rather constant at 25 per cent during a period of 135 days. After a year of continuation, however, both populations reached the same lethal frequency of about 10 per cent. Allelism tests carried out after 10 generations revealed that there was a highly heterotic lethal factor in the homozygous population. After excluding this heterotic lethal from the calculations, the lethal frequencies of the two populations remained significantly different. It was assumed that the relative mean fitness of lethal heterozygotes was generally higher in the homo-than in the heterozygous populations. The results indicate that homozygous populations are much more capable of incorporation new mutations than heterozygous.     

Prevalence of diabetes mellitus in individuals heterozygous and homozygous for sickle cell anemia

Colorimetric determinations of glycosylated Hb were carried out in a sample (n = 97) of sickle cell anemia patients, and in an age- and sex-matched group of individuals (n = 45) heterozygous for sickle cell anemia, from the Eastern Province of Saudi Arabia. A statistically significant increase in the value of glycosylated Hb was found in sickle cell trait (HbAS) group, when compared with those of sickle cell anemia (HbSS) and normal (HbAA) groups. Since glycosylated Hb is considered a valid indicator of long-term blood glucose, and assuming normal red blood cell survival in HbAS carriers, the increased value of glycosylated Hb may suggest that there exists a higher incidence of undiagnosed diabetes mellitus in individuals with heterozygous inheritance for sickle cell hemoglobin than homozygous sickle cell patients and normal individuals. The mechanism underlying this observation remains to be defined.     

QTL analysis of morphological traits in a tomato recombinant inbred line population.

Quantitative trait loci (QTLs) influencing morphological traits were identified by restriction fragment length polymorphism (RFLP) analysis in a population of recombinant inbred lines (RILs) derived from a cross of the cultivated tomato Lycopersicon esculentum with a related wild species, Lycopersicon cheesmanii. One hundred and thirty-two RFLP loci spaced throughout the tomato genome were used as DNA probes on genomic DNA from 97 RIL families. Morphological traits, including plant height, plant fresh mass, number of branches, number of nodes, first flower-bearing node, and leaf length, were evaluated in two controlled environment trials in 1992 and 1993. QTLs were detected via regression analyses at multiple marker loci for each morphological trait. A total of 41 markers were significantly associated with the traits examined. Large additive effects were measured at many of these loci. QTLs for multiple traits were detected on chromosomes 3 (TG74) and 4 (CT188), suggesting the possible association of these chromosome segments with genes controlling growth and development in tomato. These chromosomal regions were also associated with multiple morphological traits in a L. esculentum x Lycopersicon pennellii cross. A total of 13% of the QTLs identified for traits common to both studies occupied similar map positions.     

Modifications of transthyretin in amyloid fibrils: analysis of amyloid from homozygous and heterozygous individuals with the Met30 mutation.

The finding of individuals homozygous for FAP I (familial amyloidotic polyneuropathy, transthyretin TTRMet30) with amyloid deposits in the vitreous body, gave us access to a unique material lacking wild type transthyretin and contaminating proteins. Amyloid TTR is modified in several ways. Besides the full-length protein and its dimer form, two smaller bands were identified by SDS-PAGE and protein sequencing. One corresponded to a peptide starting at amino acid Thr49, the other was a mixture of two peptides starting at positions 1 and 3 in a 3:1 ratio. Upon reduction the amount of the TTR dimer decreased, the monomer amount increased, and the resulting monomers became available for carboxymethylation. Moreover, the mobility of the small band, which includes Cys10, increased upon reduction. This cysteine seemed to be involved in an interchain disulfide bridge both between intact TTR molecules and between small fragments. The same pattern was found in heterozygous fibril material although smaller amounts of the truncated peptides were found. Fibrils were formed both from normal and mutated TTR in heterozygotes. The significance of our results for amyloid formation is discussed.     

Pedigree analysis and inbreeding effects over morphological traits in Campolina horse population

Genetic improvement, without control of inbreeding, can go to loss of genetic variability, reducing the potential for genetic gains in the domestic populations. The aim of this study was to analyze the population structure and the inbreeding depression in Campolina horses. Phenotype information from 43 465 individuals was analyzed, data provided by the Campolina Breeders Association. A pedigree file containing 107 951 horses was used to connected the phenotyped individuals. The inbreeding coefficient was performed by use of the diagonal of the relationship matrix and the genealogical parameters were computed using proper softwares. The effective population size was estimated based on the rate of inbreeding and census information, and the stratification of the population was verified by the average relationship coefficient between animals born in different regions of Brazil. The effects of inbreeding on morphological traits were made by the use of inbreeding coefficient as a covariate in the model of random regression. The inbreeding coefficient increased from 1990 on, impacting effective population size and, consequently, shrinking genetic variability. The paternal inbreeding was greater than maternal, which may be attributed to the preference for inbred animals in reproduction. The average genetic relationship coefficient of animals born in different states was lower than individuals born within the same state. The increase in the inbreeding coefficient was negatively associated with all studied traits, showing the importance to avoid genetic losses in the long term. Although results do not indicate a severe narrowing of the population until the present date, the average relationship coefficient shows signs of increase, which could cause a drastic reduction in genetic variability if inbred mating is not successfully controlled in the Campolina horse population.     

Variation in morphological traits and trait asymmetry in field Drosophila serrata from marginal populations

Drosophila serrata occurs along the eastern coast of Australia with a southern range boundary near Sydney. To compare levels of phenotypic variation in marginal and central populations, we examined morphological variation in populations of this species from the southern range boundary and two more northerly populations. The populations differed for wing traits and there was an increase in wing size in the marginal locations which persisted under laboratory culture. The means of wing and bristle traits increased under laboratory culture, whereas wing trait coefficients of variation and variances decreased. Heritability estimates for wing size traits tended to be lower in the field compared with the laboratory, whereas bristle and crossvein length heritabilities were similar across environments. There was evidence for heritable variation in wing and bristle traits in both the marginal and more northern populations, suggesting that genetic variation was not limiting in marginal populations. Fluctuating asymmetry (FA) was also assessed as a measure of genomic and environmental stress. There were no consistent differences among populations for the FA of individual traits, or for a total FA score summed across traits. FA levels in field parents and laboratory‐reared progeny were similar. Overall, the results do not support the conjecture that levels of phenotypic and genetic variability differ between central and marginal D. serrata populations.     

Familial defective apolipoprotein B-100: a lesson from homozygous and heterozygous patients

Familial defective apolipoprotein B-100 (FDB) is a genetic disorder caused by a substitution of glutamine for arginine at residue 3500 of the apolipoprotein B-100 molecule. We have identified 23 heterozygotes and one homozygote for FDB (frequency 1:20) in a group of 510 patients with hypercholesterolemia. Mean age of the patients (18 females and 6 males) was 46 years. The diagnosis of FDB was based on point mutation PCR analysis of exon 26 of the apo B gene. Plasma lipids in heterozygous patients were: total cholesterol 8.76+/-1.2 mmol/l, triglycerides 1.42+/-0.5 mmol/l, HDL-cholesterol 1.43+/-0.3 mmol/l, LDL-cholesterol 6.69+/-1.2 mmol/l, apoB 1.69+/-0.4 g/l, Lp(a) 0.26+/-0.2 g/l. The most frequent apoE genotype was 3/3 (19 patients), apoE 3/4 genotype was found in 3 patients and one person had apoE 2/3. Xanthelasma palpebrarum was present in 4 patients and tendon xanthomas in 3 patients including the homozygote. Premature manifestation of coronary heart disease was revealed in 3 patients. Sixteen patients were treated with statins, a combination of statin and resin was used in 2 patients (including the homozygote), whereas six patients were treated with the diet only. We conclude that although the plasma lipid levels of total and LDL cholesterol in FDB patients are lower than in patients with familial hypercholesterolemia, the patients with FDB suffer from premature atherosclerosis. The therapeutic approach to FDB individuals and patients with familial hypercholesterolemia is very similar.     

Genetic analysis of root morphological traits in wheat

Traits related to root architecture are of great importance for yield performance of crop species, although they remain poorly understood. The present study is aimed at identifying the genomic regions involved in the control of root morphological traits in durum wheat (Triticum durum Desf.). A set of 123 recombinant inbred lines derived from the durum wheat cross of cvs. ‘Creso’ × ‘Pedroso’ were grown hydroponically to two growth stages, and were phenotypically evaluated for a number of root traits. In addition, meta-(M)QTL analysis was performed that considered the results of other root traits studies in wheat, to compare with the ‘Creso’ × ‘Pedroso’ cross and to increase the QTL detection power. Eight quantitative trait loci (QTL) for traits related to root morphology were identified on chromosomes 1A, 1B, 2A, 3A, 6A and 6B in the ‘Creso’ × ‘Pedroso’ segregating population. Twenty-two MQTL that comprised from two to six individual QTL that had widely varying confidence intervals were found on 14 chromosomes. The data from the present study provide a detailed analysis of the genetic basis of morphological root traits in wheat. This study of the ‘Creso’ × ‘Pedroso’ durum-wheat population has revealed some QTL that had not been previously identified.     

Physiological and morphological traits associated with zinc efficiency in Exacum

Interspecific hybrids of Exacum exhibit variation in the expression of zinc efficiency. This research investigated the genetic basis for this variation and evaluated a series of physiological and morphological traits for their association with zinc efficiency. Chi-square analyses of self-pollinated progeny from both zinc-efficient and zinc-inefficient parents indicate a significant genetic component. One hundred percent of the progeny from the inefficient parent were classified as inefficient, while the progeny from the efficient parent segregated 32% inefficient to 68% efficient. Six plants from each phenotypic class (efficient and inefficient) of the efficient parent were utilized in analyses of plant traits. Statistically significant associations were identified between the zinc-efficient phenotype and mol Zn uptake mg^-1 root, root-to-shoot ratio, specific root length, mol Zn uptake cm^-2 root surface area, and Zn uptake cm^-1 root length. No association was identified between zinc-efficient phenotype and root diameter, transpiration rate, or H⁺ production. Zinc uptake cm^-1 root length had the greatest association with the zinc-efficiency phenotype and was able to discriminate the two phenotypic classes. We suggest that Zn uptake cm^-1 root length is the most significant factor explaining the variation between the zinc-efficient and zinc-inefficient phenotypes in Exacum.     

Genetic basis of variation in morphological and life-history traits of a wild population of pink salmon

Understanding the genetic basis of phenotypic variation is essential for predicting the direction and rate of phenotypic evolution. We estimated heritabilities and genetic correlations of morphological (fork length, pectoral and pelvic fin ray counts, and gill arch raker counts) and life-history (egg number and individual egg weight) traits of pink salmon (Oncorhynchus gorbuscha) from Likes Creek, Alaska, in order to characterize the genetic basis of phenotypic variation in this species. Families were created from wild-caught adults, raised to the fry stage in the lab, released into the wild, and caught as returning adults and assigned to families using microsatellite loci and a growth hormone locus. Morphological traits were all moderately to highly heritable, but egg number and egg weight were not heritable, suggesting that past selection has eliminated additive genetic variation in egg number and egg weight or that there is high environmental variance in these traits. Genetic correlations were similar for nonadjacent morphological traits and adjacent traits. Genetic correlations predicted phenotypic correlations fairly accurately, but some pairs of traits with low genetic correlations had high phenotypic correlations, and vice versa, emphasizing the need to use caution when using phenotypic correlations as indices of genetic correlations. This is one of only a handful of studies to estimate heritabilities and genetic correlations for a wild population.     

羊草种群生态和演化形态学特性的比较研究

对单优种羊草种群的演普及演化规律的分析表明,黑钙土型羊草植物体结构简单,盐碱土型羊草结构复杂,演化出进化程度较高的通气组织、保护组织、薄壁组织及输导组织等．研究结果表明,不同土壤型羊草具有明显的种内差异．     

H-deficient blood groups of Reunion Island. III. alpha-2-L-fucosyltransferase activity in sera of homozygous and heterozygous individuals

Small amounts of H-enzyme activity (from 500 to 1,280 counts per minute [cpm]) were detected in sera of white H-deficient individuals (h/h; Reunion phenotype), while no significant H activity (less than 500 cpm) could be detected in sera of Indian H-deficient individuals (h/h; Bombay phenotype). The H-enzyme levels of the unaffected members of H-deficient pedigrees showed an H-related dosage effect. Heterozygous H/h individuals had only half as much H activity in sera (17,000 +/- 3,400 cpm) compared with homozygous H/H individuals (31,600 +/- 3,700 cpm). Data suggesting interactions between the H enzyme and the other gene specified glycosyltransferases working on the same oligosaccharide chains carrying combined ABH and Lewis antigens are analyzed in terms of their possible genetic or biochemical origin.     

亚高寒草甸不同坡向植物光合生理和叶片形态差异

绿色植物叶片的功能性状能用来解释不同层次复杂的生态学过程,被认为对植物的生存、生长和繁殖具有重要的影响。该研究对甘南亚高寒草甸坡向梯度代表物种的叶片形态和光合特性进行测定,分析了各坡向的土壤因子,比较不同物种(矮嵩草、米口袋、蒲公英和金露梅)之间的性状差异,研究叶片光合及形态特征与土壤因子之间的相关性。结果表明:1)不同坡向的土壤因子有着显著差异,土壤含水量、土壤全磷、土壤全氮及有机碳含量总体表现为北坡南坡,而土壤温度及光照度则是南坡北坡。2)坡向上不同物种在比叶面积、净光合速率和叶δ~(13)C值等方面有着显著的差异,比如物种在北坡具有较高的比叶面积和叶片含水量,而物种在南坡具有较高的净光合速率、相对叶绿素、叶干物质量及δ~(13)C值。3)冗余分析结果显示,物种的叶片形态及光合特性与土壤因子之间都具有显著的相关关系,其中土壤含水量变化的响应最为敏感。该研究揭示了亚高寒草甸坡向梯度上植物物种在叶片功能性状上的显著分化,使得这些物种能在同一个草地群落中共存。     

Evolution of novel morphological and reproductive traits in a clade containing Antirrhinum majus (Scrophulariaceae)

Phylogenetic analysis of DNA sequences of the chloroplast genes rcbL and ndhf revealed a highly supported clade composed of the families Plantaginaceae, Callitrichaceae, and Hippuridaceae in close association with the model organism Antirrhinum majus and other members of family Scrophulariaceae. Plantago has miniature actinomorphic wind-pollinated flowers that have evolved from zygomorphic animal-pollinated precursors. The aquatic Hippuridaceae have reduced windpollinated flowers with one reproductive organ per whorl, and three, rather than four, whorls. In monoecious aquatic Callitrichaceae, further reduction has occurred such that there is only one whorl per flower containing a single stamen or carpel. Optimization of character states showed that these families descended from an ancestor similar to Antirrhinum majus. Recent studies of plant developmental genetics have focused on distantly related species. Differences in the molecular mechanisms controlling floral development between model organisms are difficult to interpret due to phylogenetic distance. In order to understand evolutionary changes in floral morphology in terms of their underlying genetic processes, closely related species exhibiting morphological Variation should be examined. Studies of genes that regulate morphogenesis in the clade described here could aid in the elucidation of a general model tot such fundamental issues as how changes in floral symmetry, organ number, and whorl number are achieved, as well as providing insight on the evolution of dicliny and associated changes in pollination syndrome.     

A craniofacial morphological study of a population of northern Greek children

689 boys and 644 girls of a northern Greek children population have been studied concerning the head and face shape by means of principal component analysis. From the morphological patterns show a homogenic population with small shape differences due mainly to vertical and ear variables. Size differences appear to be responsible for the variability of the population.     

Quantitative trait loci analysis of morphological traits in Citrus

The objectives of this study were to understand the genetic basis of morphological variation observed in the genus Citrus and its relatives and to identify genomic regions associated with certain morphological traits using genetic linkage mapping and quantitative trait loci (QTLs) analysis with random amplified polymorphic DNA (RAPD) markers. First, a genetic linkage map was constructed with RAPD markers obtained by screening 98 progeny plants from a {Citrus grandis × [C. paradisi × Poncirus trifoliata]} × {[(C. paradisi × P. trifoliata) × C. reticulata] × [(C. paradisi × Poncirus trifoliata) × C. sinensis]} intergeneric cross. The map contains 69 RAPD markers distributed into nine linkage groups. Then, 17 different morphological traits, including six tree and two leaf characters of 98 progeny plants and six floral and three fruit characters of about half of the same progeny plants were evaluated for 2 years and statistically analyzed for variation. Statistical analysis of individual traits indicated that trunk diameter and growth, tree height, canopy width, tree vigor and growth, leaf length and width, petal and anther numbers, petal length and width, length of pistil and style, fruit length and diameter, and fruit segment number showed normal or close to normal distribution, suggesting that these traits may be inherited quantitatively. Quantitative data from the morphological traits were analyzed to detect markers and putative QTLs associated with these traits using interval mapping method. QTL analysis revealed 18 putative QTLs of LOD > 3.0 associated with 13 of the morphological traits analyzed. The putative QTLs were distributed in several different linkage groups, and QTLs associated with similar traits were mostly mapped to the same LG or similar locations in the linkage group, indicating that the same genomic region is involved in the inheritance of some of the morphological traits.     

Epistasis and dominance: evidence for differential effects in life-history versus morphological traits

Dominance and epistatic effects are predicted to be larger in life-history than in morphological traits. We test these predictions using published results from line cross analyses. We find that dominance is found in more than 95% of traits, regardless of the type of trait, but that the magnitude of the effect in relation to the additive effect is much greater in life-history than in morphological traits. Epistatic effects were detected more often in life-history than in morphological traits (79% and 67%, respectively). We also test for a difference in the magnitude of the effects by comparing the ratio of the nonadditive components separately to the additive component. For both dominance and epistatic components, the ratio of the nonadditive component to additive effects in life-history traits is approximately twice as large as that for morphological traits.     

Interspecific allometry of morphological traits among trematode parasites: selection and constraints

Developmental constraints and selective pressures interact to determine the strength of allometric scaling relationships between body size and the size of morphological traits among related species. Different traits are expected to relate to body size with different scaling exponents, depending on how their function changes disproportionately with increasing body size. For trematodes parasitic in vertebrate guts, the risk of being dislodged should increase disproportionately with body size, whereas basic physiological functions are more likely to increase in proportion to changes in body size. Allometric scaling exponents for attachment structures should thus be higher than those for other structures and should be higher for trematode families using endothermic hosts than for those using ectotherms, given the feeding and digestive characteristics of these hosts. These predictions are tested with data on 363 species from 13 trematode families. Sizes of four morphological structures were investigated, two associated with attachment (oral and ventral suckers) and the other two with feeding and reproduction (pharynx and cirrus sac). The scaling exponents obtained were generally low, the majority falling between 0.2 and 0.5. There were no consistent differences within families between the magnitude of scaling exponents for different structures. Also, there was no difference in the values of scaling exponents between families exploiting endothermic hosts and those using ectotherms. There were strong correlations across families between the values of the scaling exponents for the oral sucker, the ventral sucker and the pharynx: in families where the size of one trait increases relatively steeply as a function of body size, the same is generally true of the other traits. These results suggest either that developmental constraints link several morphological features independently of their specific roles or that similar selection pressures operate on different structures, leading to covariation of scaling exponents. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 96 , 533–540.