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Genetics and Genomics

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Effects of Decreased Frequency of Crossovers in Yeast

GENES-GJDIFR

You are working with a mutant yeast that dramatically reduces the frequency of crossovers during meiosis. Looking at crossover frequency in yeast is fairly easy as the haploid spores can be observed directly. With multiple auxotrophies on one chromosome, the number of crossovers can be easily determined.

In this mutant, you would expect the map distances you calculate between genes to be

, as compared to those measured in a wild-type yeast.

When examining the spores of many yeast that were induced to undergo meiosis, you find that the majority give the normal four spores as expected. However, a few yield only two live spores. The most likely cause of this abnormality is

.

Given this abnormality, you would expect the live spores in these groups to have

.