Genetics of Ascospore Color in Sordaria lab

Essay by emiliojapUniversity, Bachelor'sA+, August 2003

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To achieve genetic experiments with haploid organisms, genetic strains of different genotypes must be crossed from one another. Following fertilization and meiosis, the meiotic products can be analyzed as the ascomycete fungus, Sordaria fimicola. Sordaria can be used as a model to study meiotic segregation. The trait followed was the ascospore color. Ascospore color is a single gene trait therefore it is easily observed under a light microspore. Which allele is dominant is very tough to say, because dominant and recessive does not apply in this case. Sexual spores are confined in a saclike form called asci (singular - ascus). Inside the asci, karyogamy occurs and combines the two parental genomes, and then meiosis forms genetically diverse ascospores. Eight ascospores can be found lined up in a row in the asci; they form a single zygote, which is diploid.

These arrangements provide scientists to study genetic recombination. The genetic differences between mycelia grown form ascospore taken from one ascus that reflect crossing over and independent assortment of chromosomes during meiosis.

An interesting fact about ascospore arrangements is that there occurs no hybridization, and there are peculiar forms of cross over. Ascomycetes can also reproduce asexually by spores called conidia, which are spores that are dispersed by wind and are produced at the end of the hyphae. Another interesting fact about Sordaria is the ability to maintain a constant liner order, permitting the observer to detect the behavior of chromosomes during meiosis. The genetic experiment consists of performing the crossing over of black spores (wild type +) and tan spores (mutant n).

Materials and Methods:

Two weeks before the fungi lab, crosses between the wild type and the tan strains of Sordaria are prepared. Each lab member needs a Petri plate with a sterile crossing agar. A wax is...