Gene Mutations

Question 1

What is a gene mutation?

Answer 1

A change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide.

Question 2

Why might mutations occur?

Answer 2

Errors in copying of DNA during replication

Question 3

Why don’t most mutations actually change the polypeptide coded for?

Answer 3

Genetic code is degenerate, so several codons code for the same polypeptide. Therefore, the new codon produced may code for the same protein.

Question 4

What are insertions?

Answer 4

A new nucleotide is inserted into the DNA sequence, leading to a frame shift.

Question 5

What is substitution?

Answer 5

Where a base is swapped for another base.

Question 6

What is a deletion?

Answer 6

Where a nucleotide is removed from the DNA sequence.

Question 7

What is the template strand in DNA?

Answer 7

The strand complimentary to the coding strand of DNA.

Question 8

Name 3 chromosome mutations.

Answer 8

Translocation
Inversion
Duplication

Question 9

Name 3 types of substitution mutation.

Answer 9

Silent
Missense
Nonsense

Question 10

What are silent mutations?

Answer 10

The mutation does not alter the amino acid sequence of the polypeptide (this is because certain codons may code for the same amino acid as the genetic code is degenerate)

Question 11

What are missense mutations?

Answer 11

The mutation alters a single amino acid in the polypeptide chain

Question 12

What are nonsense mutations?

Answer 12

The mutation creates a premature stop codon (signal for the cell to stop translation of the mRNA molecule into an amino acid sequence), causing the polypeptide chain produced to be incomplete and therefore affecting the final protein structure and function

Question 13

What is an inversion mutation?

Answer 13

Where a section of chromosome breaks off, rotates 180 degrees and re-joins again

Question 14

When are inversion mutations most likely to occur?

Answer 14

During meiosis

Question 15

Usually, what happens to the protein produced after inversion has occurred?

Answer 15

The protein is typically non functional..

Question 16

Why are inversion mutations harmful?

Answer 16

The mutation is often harmful because the original gene can no longer be expressed from that chromosome

Question 17

How might the effect of an inversion mutation be lessened?

Answer 17

If the other chromosome in the pair carries a working gene the effect of the mutation may be lessened.

Question 18

What are duplication mutations?

Answer 18

A whole gene or section of a gene is duplicated so that two copies of the gene/section appear on the same chromosome.

Question 19

Why are duplication mutations not harmful to the chromosome?

Answer 19

The original gene remains intact.

Question 20

Why are duplications important?

Answer 20

They lead to evolution.

Question 21

What are translocation mutations?

Answer 21

A gene is cut in 2 places and the section that is cut attached elsewhere to a separate gene.

Question 22

In translocation, after the section is cut, why is the gene no longer functional?

Answer 22

Because a large section is missing from the gene.

Question 23

How can translocation lead to tumours?

Answer 23

If a section of a proto-oncogene is translocated onto a gene controlling cell division, it could boost expression and lead to tumours.

Question 24

How can translocation of a tumour suppressor gene lead to cancer?

Answer 24

Translocation of this gene causes it to become faulty. Therefore, when the cell replicates, the DNA will be faulty.

Question 25

What does downstream mean?

Answer 25

Further down the genetic sequence.

Question 26

Insertion of viral DNA into a host cells genes may cause the cell to make a non functional protein - explain how.

Answer 26

Insertion causes a frame shift of bases which causes a different sequence of amino acids to be produced.
Therefore, the protein may not carry out its expected function.