Involvement Of Major Genes Research Articles

Combining Ability Analysis and Genetic Studies of Stripe Rust Resistance in Bread Wheat Genotypes

A set of eighteen F1 and F2 experimental crosses were grown in a randomized complete block design (RCBD) with three replications. From lines, TD-1 was on top by showing greater and significant general combining ability (GCA) effects for maximum number characters including grain yield in both (F1 and F2) populations, while tester Benazir remained exceptional by showing higher and significant specific combining ability (GCA) effects for majority traits including grain yield in F1 and F2 populations, as a result, both parents would contribute significantly to the improvement of the bread wheat. Regarding the SCA effects in F1 population, the hybrids TD-1 × Pakistan-2013, TJ-83 × Benazir, and NIA-Sundar × NIA-Sarang and from F2 populations, the crosses TD-1 × Benazir, TJ-83 × Benazir, Kiran-95 × NIA-Sarang and NIA-Amber × Pakistan-2013 expressed desirable and maximum SCA effects for number of traits including grain yield, thus may be preferred in future wheat breeding programs. Disease reaction on selected 18 F2 populations was performed, the introgression stripe rust resistance showed single dominant gene. The genetic analysis reported the involvement of major genes for stripe rust resistance. These findings could be used to grow high-yielding wheat lines that could have a profitable yield in stripe rust-prone areas.

Genome-wide association studies reveal novel loci for resistance to groundnut rosette disease in the African core groundnut collection

Key messageWe identified markers associated with GRD resistance after screening an Africa-wide core collection across three seasons in UgandaGroundnut is cultivated in several African countries where it is a major source of food, feed and income. One of the major constraints to groundnut production in Africa is groundnut rosette disease (GRD), which is caused by a complex of three agents: groundnut rosette assistor luteovirus, groundnut rosette umbravirus and its satellite RNA. Despite several years of breeding for GRD resistance, the genetics of the disease is not fully understood. The objective of the current study was to use the African core collection to establish the level of genetic variation in their response to GRD, and to map genomic regions responsible for the observed resistance. The African groundnut core genotypes were screened across two GRD hotspot locations in Uganda (Nakabango and Serere) for 3 seasons. The Area Under Disease Progress Curve combined with 7523 high quality SNPs were analyzed to establish marker-trait associations (MTAs). Genome-Wide Association Studies based on Enriched Compressed Mixed Linear Model detected 32 MTAs at Nakabango: 21 on chromosome A04, 10 on B04 and 1 on B08. Two of the significant markers were localised on the exons of a putative TIR-NBS-LRR disease resistance gene on chromosome A04. Our results suggest the likely involvement of major genes in the resistance to GRD but will need to be further validated with more comprehensive phenotypic and genotypic datasets. The markers identified in the current study will be developed into routine assays and validated for future genomics-assisted selection for GRD resistance in groundnut.

A Genome-Wide Scan Divulges Key Loci Involved in Resistance to Aphids (Aphis craccivora) in Cowpea (Vigna unguiculata).

Cowpea aphids (Aphis craccivora Koch) double as a direct damaging pest and a virus vector to cowpea, threatening the economic yield of the crop. Given the multiple ecotypes, different alleles have been implicated in aphid resistance, necessitating the identification of key genes involved. The present study implemented a genome-wide scan using 365 cowpea mini-core accessions to decipher loci involved in resistance to aphid ecotype from Kano, Nigeria. Accessions were artificially inoculated with A. craccivora in insect-proof cages and damage severity assessed at 21 days after infestation. Significant phenotypic differences based on aphid damage severity were registered among the accessions. Skewed phenotypic distributions were depicted in the population, suggesting the involvement of major genes in the control of resistance. A genome-wide scan identified three major regions on chromosomes Vu10, Vu08 and Vu02, and two minor ones on chromosomes Vu01 and Vu06, that were significantly associated with aphid resistance. These regions harbored several genes, out of which, five viz Vigun01g233100.1, Vigun02g088900.1, Vigun06g224900.1, Vigun08g030200.1 and Vigun10g031100.1 were the most proximal to the peak single nucleotide polymorphisms (SNPs) positions. These genes are expressed under stress signaling, mechanical wounding and insect feeding. The uncovered loci contribute towards establishing a marker-assisted breeding platform and building durable resistance against aphids in cowpea.

Aspects of reproductive performance in small ruminants – opportunities and challenges

Ovulation rate is the principal source of variation in the reproductive rate of small ruminants. There is extensive variability in this trait both in terms of major genes and polygenes. Identification of the DNA changes responsible for the Booroola and Inverdale effects enabled testing for these mutations in any population. Surprisingly, in only one of six populations, with segregation of major genes for ovulation rate, could the effect be attributed to one of these mutations. Current evidence shows that there are five distinct loci that have large effects on ovulation rate. Selection on ovulation rate in Finn sheep produced a 2.2-fold change without any evidence for major gene involvement. The response appears to reflect changes in the thresholds that control the number of ova shed, indicating that a fundamentally different mechanism is involved from those shown for Booroola and Inverdale genes, and probably other major genes. The results also indicate that the variability of ovulation rate, for a given mean value, can be reduced by genetic selection. This has direct implications for neonatal survival, which declines rapidly as the size of the litter at birth increases above two - a major limitation on the exploitation of the known major genes. The effectiveness of genetic improvement programmes, especially in sheep, would be greatly enhanced if the problem of poor pregnancy rate from cervical insemination of frozen-thawed semen was solved. Recent studies reveal major differences among ewe breeds and large ram-to-ram variation in pregnancy rate from cervical AI with frozen-thawed semen. Identification of the basis for ram-to-ram variation could be exploited immediately in selecting rams for AI. Progress in this area would greatly facilitate the exploitation of molecular genetic information in the genetic improvement of small ruminants.

Genetic Determinants of 22 Quantitative Dermatoglyphic Traits in the Chuvashian Population of Russia: Complex Segregation Analysis

Background: Dermatoglyphics is widely used as a genetically determined trait in Anthropology. However, little is known about their pattern of inheritance due to lack of advanced statistical genetic model-fitting techniques despite the existence of advanced statistical packages. Objectives: The aim of the present study is to determine the mode of inheritance of dermatoglyphic traits through complex segregation analysis. Subjects and Methods: Finger and palmar prints of 325 individuals belonging to 104 families from the Chuvashian popu- lation of Russia were used for principal component analysis, familial correlation, and segregation analysis (package MAN-5). Results: The results suggest a common internal structure of three factors when compared with other populations. (b) Sig- nificant familial correlations (except spouse) indicate the involvement of familial components to the variation of dermato- glyphic traits. (c) Segregation analysis reveals the transmission of genetic effects in the families, which follows the Men- delian model and confirm major gene effect on factors 1 and 2, whereas there is no evidence of major gene effect or an environmental effect on factor 3. Conclusion: Major gene involvement with Mendelian expectation regarding finger dermatoglyphics is confirmed for all analyzed traits. However there is no evidence of significant support for major gene effect or environmental effect on pal- mar a-b ridge counts.

Mapping QTLs for Witches' Broom (Crinipellis Perniciosa) Resistance in Cacao (Theobroma Cacao L.)

Molecular markers (RAPD, AFLP and microsatellites) were used to generate a linkage map and to identify QTLs associated to witches' broom (Crinipellis perniciosa) resistance in cacao (Theobroma cacao), using 82 individuals of an F2 population derived from the clones ICS-1 (susceptible) and Scavina-6 (resistant). Fifteen evaluations of the number of brooms have been carried out in six years (1997–2002). In order to increase the precision and accuracy in the measures of resistance, each F2 plant was cloned in three replications in a randomized block design with single-tree plots and evaluated over 2 years. Three hundred and forty-two markers were obtained, being 33 microsatellites, 77 AFLPs and 232 RAPDs. The distribution of the number of brooms in the F2 population was skewed to resistance, suggesting the involvement of major genes controlling resistance and the repeatability estimated for resistance was 44%. A strong putative QTL was detected as being related to witches' broom resistance. Associated to this QTL, the microsatellite mTcCIR35 explained 35.5% of the phenotypic variation in resistance. This marker is being used for marker-assisted selection in Scavina-6 progenies, including those selected in private plantations, as an auxiliary tool to the phenotypic selection.

Mode of inheritance of dermatoglyphic pattern intensity index on fingers in five Indian populations: A comparative study between individual trait and its factor

Our previous study (Karmakar et al. 2005 Ann. Hum. Biol. 32:445-468) was on 500 pedigrees of five different populations, with factor 1 comprising quantitative finger dermatoglyphics (including pattern intensity index, PII) and factor 1 controlled by major genes. The present results of a complex segregation analysis of the individual trait PII of the same five populations were compared with previous results to ascertain the extent of variation between individual trait PII and its factor (factor 1) with respect to mode of inheritance. The comparative findings are very similar in five populations, irrespective of different ethnic groups. This result suggests that the variability of their biological relevance is influenced by the same genetic component, thus representing a similar mode of inheritance with major gene involvement in all populations.

Complex segregation analysis of quantitative dermatoglyphic traits in five Indian populations

Objective: Dermatoglyphics is widely used as a genetically determined trait in anthropogenetics although the genetic nature of its inheritance is still inconclusive, due to the lack of any established genetic model to resolve the existing inconsistencies in the literature. However, advanced statistical packages for complex segregation analyses are available and the aim of the present study is to determine the mode of dermatoglyphic trait inheritance in five different ethnic populations. Methods: Five hundred families (2435 individuals) of two generations were used for principal component analysis, familial correlation and segregation analysis (package MAN-5). Results: The similarity of three factors suggests a common internal structure. Significant familial correlation (except spouse) indicates the involvement of a familial component in the variation of dermatoglyphic traits. Segregation analyses suggest the transmission of a genetic effect in the families which follows the Mendelian model and confirms a major gene effect on factor 1 and factor 2 with two co-dominant alleles. There is no evidence of a major gene effect or environmental effect on factor 3 (a–b ridge counts). The nature of transmission and trait variance (H2) strongly supports the existence of a common nature of dermatoglyphic trait inheritance in populations, irrespective of ethnic and geographic area. Conclusion: Major gene involvement in finger dermatoglyphics according to Mendelian models is confirmed.

Genetic epidemiology with a capital ?E?

Three characteristics of genetic epidemiology that distinguish it from its parent disciplines are a focus on population-based research, a focus on the joint effects of genes and the environment, and the incorporation of the underlying biology of the disease into its conceptual models. These principles are illustrated by a review of the genetic epidemiology of breast and ovarian cancer. Descriptive and mechanistic models for the joint effects of genes and "environmental" risk factors such as hormones and reproductive events are compared to illustrate the need to understand the biology. The contribution of population-based research to the development of the evidence for the involvement of major genes, the discovery of BRCA1 and BRCA2, and their characterization is reviewed. Interactions of major susceptibility genes, metabolic genes, and hormones are also discussed. I conclude with some suggestions for future directions for the field, the journal, and the Society, including recent bioethics initiatives. I believe that the Society should reach out more to the epidemiology community and that the journal should shift its emphasis from pure methodology to also include more substantive papers that illustrate these principles.

Inheritance of heart rate variability: the kibbutzim family study.

Heart rate variability (HRV) measures are associated with coronary heart disease incidence and mortality. Therefore insight into the genetic and environmental determinants of these measures may have clinical relevance. We assessed the role of genetic and environmental factors of time domain and frequency domain HRV indices. Participants were 451 kibbutz members, aged 15 and up, belonging to 80 families. HRV indices were calculated from Holter recordings measured over 5 min. Our data indicate that for the two time- and four frequency domain indices, a mixture of two normal distributions fit the data significantly better than a single normal distribution (P<0.05). We used complex segregation analysis to infer the modes of inheritance of these HRV measures. We found evidence for possible involvement of a recessive major gene in the inheritance of the root mean square of successive differences in RR intervals (RMSSD), which is predominantly vagally mediated. A putative major gene explains 28%-34% of the adjusted inter-individual variability. The SD, determined by a mixture of mechanisms, is influenced by environmental and polygenic effects, but not by a major gene. The findings regarding the heritability of the frequency domain indices were not conclusive. However, the involvement of genetic factors was not rejected. Additional studies in extended families are needed to confirm the involvement of major genes in the determination of the autonomic activity.

Resistance to two-spotted spider mite Tetranychus urticae in strawberry cultivars and wild species of Fragaria and Potentilla

SummaryCultivars of strawberry and wild species of Fragaria and Potentilla were tested for resistance to two-spotted spider mite, Tetranychus urticae, mainly by recording the numbers of eggs laid over a standard period. On some clones of F. chiloensis significantly fewer eggs were laid than on the standard, cv. Elsanta, in no-choice tests, and fewer eggs were laid on clone DL-40 than ‘Elsanta’ in a choice test. Differences were detected in the numbers of eggs laid on individual strawberry cultivars tested, but, as with the F. chiloensis clones, the results of the experiments showed inconsistencies. The number of eggs laid and the time for development from egg to adult were similar overall on newly-propagated plants and one year old plants that had experienced dormancy and chilling. However, some cultivars, and clone DL-40, gave results significantly different from ‘Elsanta’ for these parameters. Results from experiments with the progeny of crosses using cultivars/clones showing reduced fecundity did not suggest the involvement of major genes, since there was no clear segregation between resistant and susceptible categories in either the F1 or F2 generations. No reductions in the numbers of eggs laid were found in the species of Potentilla tested.

Genetic contributions to LDL-C, Apo-B and LDL-C/Apo-B ratio in a sample of Israeli offspring with a parental history of myocardial infarction.

One hundred and forty sibships consisting of 280 brothers and 256 sisters with a family history of myocardial infarction were investigated for the possible involvement of a major gene in the determination of LDL-C, Apo-B and LDL-C/ Apo-B ratio (as a surrogate for LDL subclasses). The mean ages were 29.5 years (range 15-48) and 29.2 years (range 15-47), for brothers and sisters, respectively, and values were initially adjusted for age effects through multiple regression analysis. Results from commingling analysis indicated that for LDL-C a single normal distribution fitted the data as well as a mixture of two distributions. For Apo-B, a mixture of two normal distributions fitted the data significantly better than a single distribution (chi 2 = 7.8, df = 2, p = 0.02). For LDL-C/ Apo-B ratio a mixture of three normal distributions fitted the data significantly better than two distributions (chi 2 = 9.2, df = 2, p = 0.01). A regression analysis applied to the logarithm of the sex- and age-adjusted mean and variance within sibship, showed no indication of a major gene involvement for LDL-C. For Apo-B and LDL-C/Apo-B ratio, there existed, however, significant linear relationships between the logarithmically transformed means and within sibship variances which support the involvement of major genes. In addition, the Bartlett test applied to the data of within-sibship variances also rejected the null hypothesis of multifactorial transmission for Apo-B and LDL-C/Apo-B ratio (p < 0.0001). Lastly, the results from sib-pair linkage analyses provided significantly positive evidence for linkage between ApoB levels and the Apo-B XbaI restriction site.

Major gene involvement in human obesity

Major gene involvement in human obesity

Genetic influences on spatial ability: transmission in an extended kindred.

Transmission of six spatial tests, Card Rotations, Cube Comparisons, Group Embedded Figures, Hidden Patterns, Mental Rotations, and portable Rod and Frame, is examined among 73 members in four generations of an extended kindred. Nonadditive genetic variance is substantial for one of the six tests, Card Rotations. Whether this nonadditive genetic variance is due to a major autosomal gene is equivocal based on results from segregation and linkage analysis. There is no evidence for genetic variance for Mental Rotations or Hidden Patterns, in contrast to previous findings suggesting major gene involvement (Ashton et al., 1979). If spatial ability is due, in part, to an autosomal major gene, the gene has variable expression (reflected in different tests) or genetic heterogeneity is pronounced.

Complex segregation analysis of plasma lipid and lipoprotein variables in a Jerusalem sample of nuclear families.

Plasma lipid and lipoprotein concentrations from 3,074 nuclear families in the multiethnic Jerusalem Lipid Research Clinic study population were analyzed for possible involvement of major genes in determination of high levels of these traits. Complex segregation analysis under a mixed model including major gene and multifactorial transmissible components was performed on transformed-plasma lipids and lipoproteins after covariance adjustment for age, sex and environmental measures. Likelihood analysis provided evidence for recessive major genes influencing plasma triglyceride, and low-density lipoprotein cholesterol (LDL-C). The estimated gene frequencies for triglyceride and for hyperbetalipoproteinemia in our study population were about 0.1. Our positive results for total cholesterol and high-density lipoprotein cholesterol (HDL-C) were nonconclusive and the major effects could result from causes other than major genes. The mixed-model parameters were homogeneous across origin groups for LDL-C and HDL-C and heterogeneous for total plasma cholesterol and triglyceride. The multifactorial-transmission heritability index was similar in all origin groups for all the traits. The origin heterogeneity in the major gene parameters appeared to be mainly due to the North African group which favored a multifactorial transmission for all traits except for LDL-C.

Genetic epidemiology of cleft lip with or without cleft palate in the population of Hawaii.

Orientals consisting of Japanese, Chinese, Koreans, and Filipinos are clearly at higher risk for cleft lip with or without cleft palate [CL(P)] than whites, Puerto Ricans, and Hawaiians/part-Hawaiians in Hawaii. Using the model of diallele cross, CL(P) incidences in incrosses and outcrosses involving 564,002 live births distributed among 669 mating types were analyzed to study the extent of major gene involvement in the difference in the two groups and to investigate maternal effect in the etiology of CL(P). CL(P) cases excluding syndrome cases were classified into two types: all CL(P) cases and CL(P) cases without additional malformations. For either type there was no evidence to suggest that simple major gene plays a dominant role in accounting for racial differences as measured by deviations from additivity in the hybrids. For CL(P) cases without additional defects, a negative "maternal effect" was detected in Filipinos such that higher risk for this racial group depends on when the father is Filipino. Implications of the findings are discussed.

Complex segregation analysis of low levels of plasma high-density lipoprotein cholesterol in a sample of nuclear families in Jerusalem.

Low levels of high-density lipoprotein cholesterol (HDL-C) are associated with increased risk of coronary heart disease (CHD). Therefore, assessment of the mode of inheritance of HDL-C is of importance. HDL-C concentrations in 3,074 nuclear families in the multiethnic Jerusalem Lipid Research Center study population were analyzed for possible involvement of major genes in determination of low levels of this trait. Complex segregation analysis under the mixed model of inheritance (major gene and multifactorial components) was performed on transformed HDL-C concentrations after adjustment for age, sex, and environmental measures. Evidence for segregation of a recessive major gene for depressed HDL-C, with an allele frequency of q = 0.06, in addition to multifactorial transmission (H = 0.45) was found in these families. Estimates from the mixed model were homogeneous across the different ethnic groups. When the substantial multifactorial background was excluded from the model, we found evidence for an additive (codominant) Mendelian gene (d = 0.48), which demonstrates the necessity of using the mixed model. Our previous results were inconclusive with respect to the involvement of a major gene in determination of high levels of HDL-C. However, we tentatively postulate an uncommon recessive gene for low levels of HDL-C in the Israeli population in addition to polygenic and environmental determinants.