User:Kcutshaw/sandbox

Article Evaluation
The page I evaluated was on petite mutations. Though it had some accurate information, it was not detailed and seemed redundant in a lot of places. The layout seemed clunky and not well organized, and it used a lot of primary journal articles as sources.

History
Over 50 years ago, in a lab in France, Ephrussi, et al. discovered a non-Mendelian inherited factor that is essential to respiration in the yeast, Saccharomyces cerevisiae. S. cerevisiae without this factor, known as the ρ-factor, is described by the development of small colonies when compared to the wild-type yeast. These smaller colonies were dubbed petite colonies. These petite mutants were observed to be spontaneously produced naturally at a rate of 0.1%-1.0% every generation. They also found that treatment of wild-type S. cerevisiae with DNA-intercalating agents would more rapidly produce this mutation.

Schatz identified a region of the yeast’s nuclear DNA that was associated with the mitochondria in 1964. Later, it was discovered that mutants without the ρ-factor had no mitochondrial DNA (called ρ0 isolates), or that they possessed a difference in density or amount of the mitochondrial (called ρ- isolates). The use of electron microscopy to view the DNA in the mitochondrial matrix helped to verify the actuality of the mitochondrial genome.

S. cerevisiae has since become a useful model for aging. It has been shown that as yeast ages, it loses functional mitochondrial DNA, which leads to replicative senescence, or the inability to further replicate. It has been suggested that there is a link between mitochondrial DNA loss and replicative life span (RLS), or the amount of times a cell can reproduce before it dies, as it has been found that an increase in RLS is established with the same changes in the genome that enhance the propagation of cells that do not contain mitochondrial DNA. Genetic screens for replicative life span associated genes and pathways could be made easier and quicker by selecting genetic suppressors of the petite negative mutants.

Though S. cerevisiae has been extensively studied in this and other areas, it is difficult to say if the molecular mechanisms of this process in the mitochondrial DNA are conserved across other yeast species. Other yeast species, such as Kluyveromyces lactis, Saccharomyces castellii, and Candida albicans have all shown to produce petite negative mutants. Potentially, these yeasts have a different inheritance system in place for their mitchondrial genome than S. cerevisiae does.

The frequency at which S. castellii spontaneously produces petites is similar to that of S. cerevisiae, with the mitochondrial DNA of those petites being highly altered via deletion and rearrangement. Suppressive petites of S. cerevisiae are the most commonly observed spontaneously created mutants, whereas in S. castellii, the most commonly observed spontaneous mutant is the neutral petite, further leading to speculation that the transference of this mutation differs between species.