Consanguineous unions and endogamy in families of beta-thalassaemia patients from two Mediterranean populations: Tunisia and Italy

Background: Consanguinity increases the incidence of recessive diseases such as beta-thalassaemia major (βTM), one of the most prevalent lethal inherited diseases in the world.Aim: This study aims to identify the frequency of endogamy and consanguinity in two Mediterranean βTM populations and to study the implication of socio-economic factors.Subjects and methods: A trans-sectional study was conducted in 203 Tunisian families and 75 Italian families. Data were collected using a questionnaire completed by patients and parents.Results: Complete endogamy and consanguinity were observed in 82.75% and 62.56% of Tunisian families, respectively. Complete endogamy was found in 90.67% of Italian families, no consanguinity was noted. The low occupation status of Tunisian mothers was associated with an increasing frequency of consanguinity (p = .01) and endogamy (p = .0003). Consanguinity was associated with low education level (p = .012) and low occupation status (p=.047) of fathers. No significant association was found between endogamy and socio-economic factors in the Italian sample.Conclusions: High consanguinity and endogamy rates in Tunisian families may explain the frequency of βTM in Tunisia. The high endogamy rate in Italian families could also increase the frequency of βTM. Identification of geographical distribution and socio-economic factors leading to endogamy and consanguinity in these populations might help to improve βTM prevention.

Relationship between leaf stages and epistasis for resistance to Stagonospora nodorum in durum wheat

Ten varieties and eight generations (2F1, 2F2, 2B1 and 2B2) of durum wheat derived from two crosses were evaluated for resistance to natural infection by Stagonospora nodorum blotch (SNB) at the 2-3 and 6-7 leaf stages at two sites over two years. There were significant differences in the incidence of SNB between leaf stages in most of the wheat varieties, with resistance being most evident at the 6-7 leaf stage. Separate analyses of the mean values for each generation showed that the genetic mechanism of defense against the pathogen depended upon the leaf stage. At the 2-3 leaf stage, only additive and dominance effects were implicated in the control of SNB for the two crosses at the two sites and for the two replications. For the 6-7 leaf stage, inheritance was more complicated and an epistatic effect was involved. Narrow-sense heritability values (range: 0.63-0.67) were consistent between crosses and leaf stages. These findings indicate a lack of resistance to SNB at the 2-3 leaf stage whereas resistance was observed at the 6-7 leaf stage and involved the genetic mechanisms of plant defense such as epistasis.

Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F(1) , F (2) , BC (1) Pr, and BC (1) Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn (Ko1) , Pn (Ko2) and Pn (Kr1) , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn (Bz1) , Pn (Bz2) and Pn (Kr2) , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance.

Epistasis and genotype-by-environment interaction of grain protein content in durum wheat

Parental, F₁ , F ₂ , BC ₁ and BC ₂ generations of four crosses involving four cultivars of durum wheat (Triticum durum Desf.) were evaluated at two sites in Tunisia. A three-parameter model was found inadequate for all cases except crosses Chili x Cocorit 71 at site Sidi Thabet and Inrat 69 x Karim at both sites. In most cases a digenic epistatic model was sufficient to explain variation in generation means. Dominance effects (h) and additive x additive epistasis (i) (when significant) were more important than additive (d) effects and other epistatic components. Considering the genotype-by-environment interaction, the non-interactive model (m, d, h, e) was found adequate. Additive variance was higher than environmental variance in three crosses at both sites. The estimated values of narrow-sense heritability were dependent upon the cross and the sites and were 0%-85%. The results indicate that appropriate choice of environment and selection in later generations would increase grain protein content in durum wheat.

Evaluation of genetic diversity in Aegilops geniculata Roth accessions using morphological and RAPD markers

Thirteen Aegilops geniculata Roth (geniculate goat grass) accessions from collection of the North and Central Tunisian (Cap-Bon, Mogodses, Kroumiry and the Dorsal areas) were used to assess its genetic diversity by morphological and Random Amplified Polymorphic DNA (RAPD) data and to evaluate relationship between morphological and RAPD markers. Nineteen morphological traits were analyzed on all accessions using Principal Analysis Component (PCA) and clusters were constrained based on median joining distances. Nineteen arbitrary universal primers were used for the amplification of random DNA sequences and generated 212 bands ranging from 0.5 to 3 kb with 71.27% polymorphism across the 13 accessions. Both RAPD and morphological data classified accessions in two main groups. Both methods were used to compare how morphological traits and RAPD molecular markers described accessions relationship and showed a high degree of variation among analyzed accessions, indicating an important source of genetic diversity that can be used in future breeding programs. Morphological PCA traits and cluster indicated climatic stage. In fact, they grouped Ae. geniculata accessions according to genetic criteria such as earliness and high kernel yield. Comparison of morphological and molecular data using the Mantel test indicated a non significant correlation (r = -0.268). Nevertheless, RAPD and selected morphological characters appear as useful and complementary techniques for evaluation of genetic diversity in Ae. geniculata.

[Influence of the geographical locations on the agronomical and technological potentialities of the olive tree (Olea europaea L.) in Tunisia]

This study aims at characterization four cultivars of the olive trees, Chétoui, Chemlali, Gerboui, and Chaïbi, cultivated in three different geographical locations, from pomological and technological points of view. The pomological characters of the fruit are influenced by the geographical location. Each individual of the same cultivar expresses different pomological characters. We have noted a significant fluctuation of the flush percentage in three Chaïbi individuals according to their geographical site; it varies from 49.06 to 82.19%. The three Gerboui individuals showed a significant variability of the fruit weight (from 1.13 to 3.17 g). Fluctuations of olive oil contents were also observed. Several fatty acid compositions showed some variation. The oleic and linoleic acid contents varied among individuals from Chétoui and Chaïbi. Moreover, the individuals of the cultivar Chemlali showed a variation of their content in palmitic and palmitoleic acids. Indeed, each individual of a cultivar showed its own potentialities, which are reflected by its pomological and technological characters. According to their geographical location, individuals from a given cultivar displayed diverse potentialities.

Estimation of the dominance merit in noninbred populations without recourse to its inverted relationship matrix

This study presents a new approach to obtain dominance estimates without using the full Henderson's mixed model equations (MMEs) related to an additive plus dominance animal model. This reduction could decrease substantially the computing time and hence its cost. In contrast to a procedure that we proposed before, the method developed in this paper does not require D(-1) and provides best linear unbiased prediction (BLUP) of genetic values that is close to that given by processing the full MMEs. In the previous study, we also elaborated an algorithm (denoted xi-REML) in order to approximate restricted maximum likelihood estimation of variance components via the expectation maximization (EM) algorithm. The xi-REML algorithm has been modified to be adapted to our new resolution approach. Through a numerical example, we show that there is a good agreement between REML-(EM), xi-REML and modified xi-REML estimates and that the latter algorithm is more efficient than our first proposition in terms of computing time and memory conservation.

Estimation of dominance components in noninbred populations by using additive animal model residuals

In the case of noninbred and unselected populations with linkage equilibrium, the additive and dominance genetic effects are uncorrelated and the variance-covariance matrix of the second component is simply a product of its variance by a matrix that can be computed from the numerator relationship matrix A. The aim of this study is to present a new approach to estimate the dominance part with a reduced set of equations and hence a lower computing cost. The method proposed is based on the processing of the residual terms resulting from the BLUP methodology applied to an additive animal model. Best linear unbiased prediction of the dominance component d is almost identical to the one given by the full mixed model equations. Based on this approach, an algorithm for restricted maximum likelihood (REML) estimation of the variance components is also presented. By way of illustration, two numerical examples are given and a comparison between the parameters estimated with the expectation maximization (EM) algorithm and those obtained by the proposed algorithm is made. The proposed algorithm is iterative and yields estimates that are close to those obtained by EM, which is also iterative.