Selection Of Segregants Research Articles

Caracterización morfológica de híbridos de chile manzano


 
 
 El chile manzano (Capsicum pubescens R y P) cultivado en el centro de México presenta variabilidad genética aprovechable en programas de mejoramiento genético. El objetivo de la investigación fue evaluar dos métodos de hibridación y caracterizar morfológicamente los descendientes F1 de las cruzas entre morfotipos de chile manzano. El experimento se desarrolló de 2012 a 2013 en invernadero con los progenitores identificados como flor blanca (FB), Flor morada-entrenudo largo (FML) y flor morada-entrenudo corto (FMC). Se hibridaron por los métodos “sin corola y “con corola” y la F1 se evaluó a prendimiento de fruto y caracterización morfológica. Los resultados indicaron que la protección de la flor hibridada afectó el prendimiento de fruto en más del 50%. No hubo diferencias significativas entre cruzas directas ni recíprocas (t; p= 0.42), lo que sugiere ausencia de efectos maternos. La posición del estilo tanto en progenitores como en los híbridos fue heteromórfica, con 70-90% al nivel de las anteras. Los variantes de los caracteres color del tallo, color de la corola, color del filamento y color del estilo se encontraron en el progenitor FB y fueron recesivos a los correspondientes de FML y FMC. El porte bajo de la planta y hojas de menor tamaño presentes en los progenitores FB y FMC fueron dominantes en los híbridos y afectaron negativa y significativamente en el rendimiento de frutos y heterosis. Los resultados sugieren estrategias de mejoramiento genético adicionales en híbridos como selección de segregantes y retrocruzas que mejorar el tamaño del fruto.
 
 

Deleterious Mutations and Selection for Sex in Finite Diploid Populations

In diploid populations, indirect benefits of sex may stem from segregation and recombination. Although it has been recognized that finite population size is an important component of selection for recombination, its effects on selection for segregation have been somewhat less studied. In this article, we develop analytical two- and three-locus models to study the effect of recurrent deleterious mutations on a modifier gene increasing sex, in a finite diploid population. The model also incorporates effects of mitotic recombination, causing loss of heterozygosity (LOH). Predictions are tested using multilocus simulations representing deleterious mutations occurring at a large number of loci. The model and simulations show that excess of heterozygosity generated by finite population size is an important component of selection for sex, favoring segregation when deleterious alleles are nearly additive to dominant. Furthermore, sex tends to break correlations in homozygosity among selected loci, which disfavors sex when deleterious alleles are either recessive or dominant. As a result, we find that it is difficult to maintain costly sex when deleterious alleles are recessive. LOH tends to favor sex when deleterious mutations are recessive, but the effect is relatively weak for rates of LOH corresponding to current estimates (of the order 10(-4)-10(-5)).

A single-transformation gene function test in diploid Candida albicans.

The fungal pathogen Candida albicans is naturally diploid, and current gene disruption strategies require two successive transformations. We describe here a genetic construct (UAU1) for which two copies may be selected. Insertion of UAU1 into one genomic site, after a single transformation, allows selection for segregants with two copies of the insertion. Major classes of segregants are those carrying homozygous insertion mutations and allelic triplications, which have two insertion alleles and a wild-type allele. Thus nonessential and essential genes may be distinguished rapidly through PCR tests for homozygosis and triplication. We find that homozygous mutations may be isolated at three nonessential loci (ADE2, RIM20, and YGR189), while only allelic triplications were found at two essential loci (SNF1 and CDC28). We have unexpectedly isolated homozygous mutants with mutations at CDC25; they are viable but defective in filamentation on serum-containing medium. The UAU1 cassette is thus useful to assess rapidly the essentiality of C. albicans genes.