Trauma and extended separation from family among Latin American and African refugees in Montreal.

Although the vast majority of refugees have suffered trauma and extended separation from their families in exile, little is known about the interactions between these two types of experience. The qualitative and quantitative analyses of data gathered from 113 refugees from Latin America and Africa suggest that the joint occurrence of trauma and separation has a significant impact on emotional distress and confirm that the family plays a key role as an anchor of emotion and identity.

Premeiotic and Meiotic Instability Generates Numerous b2 Mutation Derivatives in Ascobolus.

We have studied the genetic characteristics of an unstable mutation located in the central region of the b2 gene of the fungus Ascobolus. In crosses to wild type, this spontaneous white ascospore mutation (G0 ) gives rise to a stable white spored derivative (G1) at a frequency of 5 x 10(-3). G1 is a frameshift mutation and differs from G0 by its gene conversion pattern. In self crosses, G0 gives asci with colored spore derivatives at a frequency of 1 x 10(-3). We isolated and analyzed genetically 97 independent colored derivatives ("G2" series). All but one are pseudorevertants. By the criteria of phenotype and gene conversion pattern with wild type and with G1, the pseudorevertants represent at least 13 distinct classes. Two of them are large silent deletion mutations. In crosses with wild type, some G2 derivatives, represented by G21, continue to exhibit instability, G21 yields white spored b2 mutant derivatives at a frequency of 2.6 x 10(-3). In turn, some of these "G3" mutants are themselves unstable. All the derivatives lie at the same site within the b2 locus as the parental mutation G0 . Different mutations in the G series manifest their instability at different times in the Ascobolus life cycle. Derivatives of G0 arise premeiotically (leading to two derivative meiotic products among the four), while those of G21 arise during meiosis (leading to only one derivative out of four products). The characteristics of the G instability system are similar to those of unstable mutations in other eukaryotes which are due to insertion of mobile elements.

Hybrid DNA formation during meiotic recombination.

G234 is a silent mutation located in the middle of gene b2, which controls spore pigmentation in Ascobolus immersus. Its effect on the aberrant segregation patterns of while spore mutants located in the same gene was investigated. When heterozygous, G234 decreases the frequency of aberrant segregations of the mutants located on its right, toward the low conversion end. It almost completely suppresses the aberrant 4:4 asci for mutants giving postmeiotic segregation and decreases the disparity between the 6 wild-type:2 mutant and 2 wild-type:6 mutant aberrant asci for mutants giving only these types of convertant asci. These effects are polar; G234 does not change the aberrant segregation pattern of the mutants located on its left, toward the high conversion end. This behavior suggests that G234 blocks the migration of the symmetric phase of hybrid DNA that diffuses from the high conversion end but does not prevent the formation of asymmetrical hybrid DNA. Taking into account previous observations, we conclude that the high conversion end corresponds to a region of asymmetric initiation of recombination rather than to a region of preferential ending of recombination. The asymmetric hybrid DNA first formed is further changed into a symmetric phase that extends via branch migration toward the low conversion end.

[High frequency reversion of a spontaneous mutant in Ascobolus immersus]. / Haute fréquence de réversion d'un mutant spontané chez Ascobolus immersus

A spontaneous spore-colour mutation located in the gene b2 of A. immersus gives a high frequency of reversion. 8 distinct revertant phenotypes have been defined. The mutations corresponding to these revertants are located at the same site or very near the original mutation. The hypothesis that the mutation by itself is responsable for the observed reversions is advanced.