8. The Control Of Gene Expression

Question 1

What are the 6 types of gene mutation

Answer 1

Substitution of bases
Addition of bases
Deletion of bases
Duplication of bases
Inversion of bases
Translocation of bases

Question 2

What are the 3 possible consequences of base substitution ?

Answer 2

• Formation of one of the 3 stop codons ie. production of polypeptide would be stopped prematurely
• Formation of a codon for a different amino acid ie. shape change
• Formation of a different codon but one that produces the same amino acid as before ie. mutation will have no effect

Question 3

What is the consequence of a base deletion ?

Answer 3

Creates a frame shift to the left
Gene is read in the wrong codons and so the coded information is altered
Polypeptide will likely lead to the production of a non-functioning protein that could considerably alter the phenotype

Question 4

What is the effect of the addition of bases

Answer 4

Usually similar effect to base deletion as there is usually a frame shift (however to the right this time)
However if 3 (or any multiple of 3) bases are added there will not be a frame shift and so the resulting polypeptide will be different but to a lesser extent than if there was a frame shift

Question 5

What is the consequence of the duplication of bases

Answer 5

One of more of the bases are repeated- produces a frame shift to the right

Question 6

What is inversion of bases and what is the consequence ?

Answer 6

A group of bases becomes separated from the DNA sequence and rejoin at the same position but in the inverse order
The base sequence of this portion is therefore reversed and affects the amino acid sequence that results

Question 7

What is the translocation of bases and what is its effect?

Answer 7

A group of bases become separated from the DNA sequence on one chromosome and reinserted into the DNA sequence of a different chromosome
Leads often to abnormal phenotype, including the development of certain forms of cancer and reduced fertility