Question

How did the discovery of three categories of petite mutations in yeast lead researchers to postulate extranuclear inheritance of colony size??

Answer 1

Answer;

Whereas segregational petites exhibited Mendelian inheritance, both neutral and suppressive petites followed non-Mendelian patterns that were consistent with the involvement of an extranuclear agent

Explanation;

• Mutations that yield defective mitochondria are expected to make cells grow much more slowly. These mutants were called petites to describe their small colonies compared to large wild type colonies.
• Petite mutants could not grow when cells had an energy source requiring only metabolic activity of mitochondria - needed sugar as well which is part of glycolytic pathway.
• Segregational petites, segregated in mendelian manner during meiosis. mutations cause defects in genes in cell nucleus encode proteins necessary for mitochondrial function.
• Vegetative petite mutants do not segregate in mendelian manner; two types: neutral and suppressive; carry mutations in mitochondrial genome itself; when two yeast cells are mated, daughter cells inherit mitochondria from both parents.
• Neutral petites lack most of their mitochondrial DNA; when mated with wildtype, the wildtype give their mitochondria so all cells display a normal phenotype.