Chapter 7 DNA Mutation, DNA Repair, and Transposable Elements

1. A question that received much attention in the early 20th century was whether mutation causes random variation leading to adaptation, or the environment induces heritable adaptations.
a. Lamarckism is the doctrine of inheritance of acquired characteristics.
b. The random mutation doctrine says that sometimes chance changes happen to be adaptive, , thus altering phenotype by changing a protein (Figure 7.1).
c. The observation that phage T1-resistant E. coli arise could be interpreted to support either of these theories.
2. Luria and Delbrück (1943) demonstrated that the mutation mechanism is correct, by doing a fluctuation test (Figure 7.2).
a. An E. coli population that started from one cell would show different patterns of T1 resistance depending on which model is correct.
i. The adaptive theory says that cells are induced to become resistant to T1 when it is added. Therefore, the proportion of resistant cells would be the same for all cultures with the same genetic background.
ii. The mutation theory says that random events confer resistance to T1, whether the phage is present or not. Cultures will therefore show different numbers of T1 resistant cells, depending on when the resistance mutation(s) occurred.
b. Luria and Delbrück observed fluctuating numbers of resistant bacteria from E. coli cultures, indicating that the random mutation model is correct.