Why are conditional mutants rare?
Well, conditional mutations are mutations that cause cell death at an extreme. For your temperature sensitive example, a conditional mutation would be one that causes cell death at high temperatures, but doesn’t at low temperatures. These are rare because causing cell death is typically detrimental to the cell, and species, so those mutations are rarely propagated. Because of their rarity, and because you cannot observe them until they begin causing cell death under monitored conditions, it’s difficult to tell them apart from regular mutations, and, thus, difficult to isolate the sequencing that allowed the mutation. Hope this helps.
