15. Gene Expression

Which of the following mutations, occurring just after the start codon in the mRNA is likely to have the most serious effects on the polypeptide product?

A nonsense mutation:

A single base substitution is LEAST likely to be deleterious (dangerous) when the change results in _____.

 A section of DNA has this base sequence: AGCGTTACCGT. A mutation in this DNA strand results in this base 

sequence: AGGCGTTACCGT. What type of mutation does this change represent?

If a base-pair change occurs in DNA, this a. is a mutation. b. would be a mutation only if it falls in a protein-coding part of a gene. c. would be a mutation only if it falls in a transcribed part of the genome. d. is not a mutation, because only one base pair has been altered.

A geneticist found that a particular mutation had no effect on the polypeptide encoded by a gene. This mutation probably involved

a. Deletion of one nucleotide

b. Alteration of the start codon

c. Insertion of one nucleotide

d. Substitution of one nucleotide

If a fragment of a chromosome breaks off and then reattaches to the original chromosome but in the reverse direction, the resulting chromosomal abnormality is called

a. A deletion

b. An inversion

c. A translocation

d. A non-disjunction

Imagine discovering a loss-of-function mutation in a eukaryotic gene. You determine the gene's nucleotide sequence from the start site for transcription to the termination point of transcription and find no differences from the wild-type sequence. Explain where you think the mutation might be and how the mutation might be acting.