Assessing population genetic structure of sorghum landraces from North-western Morocco using allozyme and microsatellite markers

 The level of genetic diversity and the population genetic structure of sorghum landraces from North-western Morocco have been investigated based on direct field-sampling using both allozyme and microsatellite markers. As expected, microsatellite markers showed a much higher degree of polymorphism than allozymes, but relative measures of genetic structure such as Wright’s inbreeding coefficient F _IS and Nei’s coefficient of genetic differentiation G _ST were similar for the two sets of markers. Substantial inbreeding was found to occur within fields, which confirms that sorghum is predominantly selfing under cultivation. Most of the genetic diversity in Moroccan landraces occurs within fields (more than 85%), as opposed to among fields or among regions, a result which contrasts to those of studies based on accessions from germplasm collections. It is suggested that individual fields of sorghum constitute valuable units of conservation in the context of in situ conservation practices. Received: 8 December 1998 / Accepted: 28 December 1998     

Partial maternal heterodisomy of chromosome 17q25 in a case of severe mental retardation

We report a segmental maternal uniparental heterodisomy of chromosome 17 (mat UPD17) in a 3-year-old boy presenting with hyperactivity, major instability, mental retardation and facial dysmorphism. Since conventional and high resolution karyotypes were normal, this patient was tested for cryptic telomeric rearrangements by using the recently developed fluorescent genotyping-based technology. The mat UPD17 segment extended for a small 11-cM region of the distal chromosome 17q. Trisomy 17 in circulating lymphocytes and skin fibroblasts was excluded. Our finding emphasizes the potential use of fluorescent genotyping to detect uniparental disomies and suggests that chromosome 17q25 should contain one or several imprinted genes of particular importance for brain development.     

Influence of Mycobacterium bovis bacillus Calmette-Guérin on antibody and cytokine responses to human neonatal vaccination.

The immaturity of the immune system increases the susceptibility of young infants to infectious diseases and prevents the induction of protective immune responses by vaccines. We previously reported that Mycobacterium bovis bacillus Calmette-Guérin (BCG) vaccination induces a potent Th1 response to mycobacterial Ags in newborns. In this study, we evaluated the influence of BCG on the response to unrelated vaccines given in early life. Newborns were randomly allocated to one of three study groups receiving BCG at birth, when infants received their first dose of hepatitis B and oral polio vaccines; at 2 mo of age, when infants received their first dose of diphtheria and tetanus vaccines; or at 4.5 mo of age, when immune responses to vaccines were measured. Administration of BCG at the time of priming markedly increased the cellular and Ab responses to the hepatitis B vaccine, but had only a limited influence on the cytokine response to tetanus toxoid and no effect on the Ab responses to tetanus and diphtheria toxoids. Although BCG induced a potent Th1-type response to mycobacterial Ags, it promoted the production of both Th1- and Th2-type cytokines in response to unrelated vaccines. The effect of BCG was apparent at the systemic level, as it increased the Ab response to oral polio vaccine. These results demonstrate that BCG influences the immune response to unrelated Ags in early life, likely through its influence on the maturation of dendritic cells.     

Le diagnostic génétique pré-implantatoire: premier bilan du groupe parisien

This paper reports the birth of the first fourteen infants conceived after preimplantation genetic diagnosis (PGD) in our unit. Fifty-nine couples were enrolled between January 2000 and July 2001. They had a total of 71 oocyte pick-up cycles. The collected oocytes were inseminated by intracytoplasmic sperm injection. The resulting embryos were biopsied on the third day of development and genetic analysis was performed on the same day. Most of the embryo transfers were carried out on the fourth day. The 71 oocyte pick-up cycles yielded 872 oocytes of which 731 were suitable for intacytoplasmic sperm injection. Among the 505 embryos obtained, 421 embryos were biopsied and genetic diagnosis was performed for 312 (74%) of them. 127 embryos were transferred during 58 transfer procedures. There were 18 biochemical and 12 ongoing (7 singles, 4 twins and 1 triple) pregnancies. Sixteen infants have been born and 2 are expected. PGD now constitutes an alternative for couples at risk of transmission of a serious and incurable genetic disease.     

On the evolution of heavy-metal tolerant populations in Armeria maritima: evidence from allozyme variation and reproductive barriers

The process of ecological differentiation leading to the evolution of heavy-metal tolerant populations in Armeria maritima was studied by comparing population genetic structure and pattern of gene flow between populations growing on heavy-metal contaminated against non-contaminated sites using allozyme markers. In addition the evolution of reproductive isolation among populations was studied by measuring pollen fertility in interpopulational hybrids. The allozyme data suggested that in A. maritima multiple independent evolutionary origins of heavy-metal tolerant populations have occurred in the absence of strong genetic bottlenecks. The pattern of gene flow among populations was consistent with the model of isolation by distance with considerable gene flow between neighbor populations, and no reduction of gene flow between tolerant and non-tolerant populations. Hence it appears that substantial gene flow has not hampered genetic differentiation, probably because of the high selection pressure for heavy-metal tolerance. The pattern of reproductive isolation among populations suggests that evolution of heavy-metal tolerant populations has not triggered the development of reproductive barriers against non-tolerant populations. However, partial reproductive isolation has occurred under geographic separation.     

A chromosome marker for the early detection of mouse embryos carrying the neural tube defect mutation splotch

A major problem in the study of neural tube defects caused by the splotch (Sp) gene in the mouse has been the identification of gene carriers or potentially affected embryos at an early stage of development, since the gene's effects become visible only late in gestation or after birth. To aid in the identification of Sp carriers, we have developed a technique using a Robertsonian translocation as a marker for this gene. The accuracy of identification is reduced by crossing-over between the Sp locus and the centromere but, because of crossover suppression in the particular cross used, there was only 23.2% recombination compared with the known map distance of 36%. Paternal age had no effect on the frequency of recombination, but individual males differed significantly in the degree of crossover suppression.     

Genetic control of the survival of murine trisomy 16 fetuses

A mouse model that allows for the experimental induction of an aneuploid state has been employed to investigate the factors that control the survival of trisomy 16 fetuses. The prevalence of trisomy 16 fetuses on day 15 of gestation was shown to vary significantly with the genetic background of the female parent. The ability to spontaneously abort a trisomy 16 conceptus was shown to be higher in the mouse strain with a low prevalence of trisomy 16, compared to those mouse strains with a high prevalence of trisomy 16. Furthermore, the maternal ability that selects against, or promotes the survival of a trisomic conceptus was shown to be specific for the trisomy in question.