DollyS
A neuron needs to travel to a particular place in the brain to do its work. Not all neurons are successful in their journey. Scientists think that only a third reach their destination. Some cells die during the process of neuronal development. Some neurons survive the trip, but end up where they should not be. Mutations in the genes that control migration create areas of misplaced or oddly formed neurons that can cause disorders such as childhood epilepsy or mental retardation. Thus, it can be concluded that misguided neurons are partly responsible for schizophrenia and the learning disorder dyslexia.
The argument assumes which of the following?
A. A disorder in a person does not affect the mutations in the genes in that person.
B. Genetic factors are not a significant cause of disorder such as childhood epilepsy or mental retardation.
C. Two third of the neurons do not reach their destination
D. No factor other than misguided neurons has an impact on disorders.
E. People with no disorder will not have areas of misplaced neurons.
ARGUMENT
[con] misguided neurons are PARTLY responsible for disorders; [prem] because mutations in the genes create areas of misplaced or oddly formed neurons that can cause disorders.
ASSUMPTION
assumes that mutations in the genes create such neurons that cause such disorders [mutations = bad neurons = disorders]; and that the inverse is not true [disorders = mutations = bad neurons].
B. not mentioned, irrelevant; out.
C. "scientists THINK that only 1/3 reach their destination" the author assumes that 1/3 is a possibility, but not a certainty, thus we cannot assume that 2/3 do not reach their destination; out.
D. "misguided neurons are PARTLY responsible" thus other factors might exist; out.
E. "create areas that CAN cause disorders" doesn't mean there aren't any such areas; out.
Answer (A)