Question

A spontaneous mutation occurs in one of the copies of MT-TK, a gene found in mitochondrial DNA. MT-TK generates a tRNA required to make proteins formitochondrial function.

a. How can this mutation become deleterious?

b. In which parent and in which cells must this spontaneous mutation occur for it to be inherited? (hint: what happens if the mutation occurs in the heart.)

Answer 1

1. A deleterious mutation is one that increases an individual's resistance or predisposition to a disease or disorder. These mutations when inherited lead to development of symptoms. Mutation in MT-TK on mitochondrial DNA becomes deleterious when it is present in the mother. Because mitochondria is inherited only from mother (maternal inheritance) but not from father. When this mutation occurs, tRNA will not be transcribed. As we know tRNA acts as an adaptor molecule in the protein synthesis and carries correct amino acid to correct genetic code and hence protein synthesis will stop.
2. This mutation will be inherited when it is present in mother (maternal inheritance) mitochondria because during fertilization only mitochondria from mother is fused but not from father and is inherited in other words an offspring gets its mitochondria from mother only. This will be inherited if this mutation occurs in the germ cells of mother that is egg. Although later once inherited it will have a major deleterious effect on the somatic cells mostly heart which don’t divide and have least probability to correct the mutation.