Chapter 20- Gene Expression

Question 1

Mutation

Answer 1

Any change to the quantity or the structure of the DNA of an organism.

Question 2

Gene mutation.

Answer 2

Any change to one or more nucleotide bases or any rearrangement of the bases.

Question 3

Substitution of bases

Answer 3

Where a nucleotide in a section of DNA is replaced by another nucleotide that has a different base.

Question 4

What are the three possible consequences of substitution of bases?

Answer 4

• Formation of one of the three stop codons.
• Formation of a codon for a different amino acid.
• Formation of a different codon but codes for the same amino acid.

Question 5

Deletion of bases

Answer 5

Creates a frame shift to the left.
Most triplets will be different and so will the amino acids that they code for.
The polypeptides will be different and lead to the production of a non functional protein which would dramatically alter the phenotype.

Question 6

When is deletion less likely to alter the sequence?

Answer 6

A deletion of a base towards the end of the sequence.

Question 7

Duplication of bases

Answer 7

One or more bases are repeated.

This produces a frame shift to the right.

Question 8

Inversion of bases

Answer 8

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

Question 9

Translocation of bases

Answer 9

A group of bases become separated from the DNA sequence on one chromosome and become inserted into the DNA sequence of a different chromosome. This leads to abnormal phenotypes.

Question 10

What are the effects of translocation of bases?

Answer 10

Cancer and reduced fertility.

Question 11

Addition of bases

Answer 11

An extra base is inserted into the sequence. There is a frame shift to the right. If any multiple of three are added, there will not be a frame shift. The resulting polypeptide will be different for, the one produced from a non-mutant gene, but not to the same extent if there was a frame shift.

Question 12

Spontaneous mutations

Answer 12

Permanent changes in DNA that occur without the outside influence.

Question 13

Mutagenic agents/ mutagens

Answer 13

Can increase the rate of mutations.

Question 14

Give two examples of mutagenic agents.

Answer 14

• High energy ionising radiation.

- Chemicals.

Question 15

High energy ionising agent.

Answer 15

Alpha and beta particles as well as short wavelength radiation (X-rays and UV light). These forms of radiation can disrupt the structure of DNA.

Question 16

Chemicals.

Answer 16

• Such as nitrogen dioxide may directly alter the structure of DNA or interfere with transcription.
• Benzopyrene inactivated a tumour suppressor gene TP53 leading to cancer.

Question 17

Give a pro for mutations.

Answer 17

Produce genetic diversity for natural selection and speciation.

Question 18

Give a negative of mutations.

Answer 18

Mostly produce organisms that are less well suited to their environment.