20.1 Gene mutations

Question 1

What are mutations?

Answer 1

A change to the base sequence of DNA

Question 2

How are mutations caused?

Answer 2

errors during DNA replication

Question 3

What are the types of mutation?

Answer 3

Substitution
Deletion
Addition
Duplication 
Inversion
Translocation

Question 4

What is Substitution?

Answer 4

one or more bases are swapped for another

Question 5

What is deletion?

Answer 5

one of more bases removed

Question 6

What is addition?

Answer 6

one or more bases added

Question 7

What is duplication?

Answer 7

One or more bases repeated

Question 8

What is inversion?

Answer 8

a group of bases become separated from the DNA sequence and rejoin in the same place in the reverse order

Question 9

What is translocation?

Answer 9

a group of bases become separated from the DNA sequence and inserted into the DNA sequence of another chromosome

Question 10

What are causes of mutations?

Answer 10

High energy ionising radiation

Chemicals

Question 11

What do deletion and addition of bases do?

Answer 11

Cause a frameshift

Question 12

What does a frameshift do?

Answer 12

Change the order of amino acids

Question 13

Why don’t all mutations affect the order of amino acids?

Answer 13

• genetic code is degenerate

- Could occur in the introns which are non-coding

Question 14

What are mutagenic agents?

Answer 14

Things which increase the rate of mutations

Question 15

Name 4 mutagenic agents

Answer 15

UV radiation
Ionising radiation
Some chemicals
Some viruses

Question 16

How do mutagenic agents work?

Answer 16

• act as a base
• Alter bases (delete or change)
• Changing structure of DNA

Question 17

define gene mutation

Answer 17

any change to one or more nucleotide bases or any rearrangement of bases in DNA

Question 18

list the types of gene mutation

Answer 18

substitution of bases
deletion of bases
addition of bases
duplication of bases
inversion of bases
translocation of bases

Question 19

what is a substitution of bases mutation?

Answer 19

a nucleotide is replaced by another of a different base.

depending on what base is substituted, there are 3 possible consequences

Question 20

what are the 3 possible consequences of a substitution of bases mutation?

Answer 20

formation of a stop codon, production of the polypeptide would be stopped and protein would most likely be significantly different, not functional
formation of a codon for a different amino acid, structure would differ slightly so protein may differ in shape and functionality
formation of different codon but same amino acid, genetic code degenerate so most amino acids have more than 1 codon, no effect on polypeptide and therefore of bases`

Question 21

what is a deletion of bases mutation? and what effect does this have?

Answer 21

base deleted causes a frame shift because each 3 letters of the code has been shifted to the left.
most triplets will be different and therefore the amino acid they code for, non-functional protein produced will significantly alter the phenotype

Question 22

what is an addition of bases mutation? and what effect does this have?

Answer 22

extra base becomes inserted into the sequence, frame shift to the right.
if 3 bases are inserted it will not have as much of an effect but would still have a different polypeptide

Question 23

what is a duplication of bases mutation? and what effect does this have?

Answer 23

one or more bases are repeated, this produces a frame shift to the right.
Effect is determined by how far to the right of the chain the mutation occurs

Question 24

what is an inversion of bases mutation? and what effect does this have?

Answer 24

group of bases becomes separated from the sequence then rejoins in the same position but in inverse order, this affects the amino acid produced.

Question 25

what is a translation of bases mutation? and what effect does this have?

Answer 25

a group of bases becomes separated from the DNA sequence on one chromosome and becomes inserted into the DNA of another chromosome.
significant effect on gene expression leading to abnormal phenotype, includes the development of certain cancers and reduced fertility

Question 26

what are the causes of mutation?

Answer 26

gene mutations can arise spontaneously during DNA replication, however can be increased by mutagenic agents

Question 27

list some examples of mutagenic agents leading to mutation

Answer 27

high energy ionising radiation - alpha and beta particles as well as short wavelength radiation such as x-rays and UV
chemicals such as nitrogen dioxide (burning of fossil fuels) and benzopyrene (tobacco smoke)

Question 28

positives of mutation?

Answer 28

produces genetic diversity necessary for natural selection and speciation

Question 29

negatives of mutation?

Answer 29

harmful
produce organisms less well suited to its environment
if in body cells leads to disruption of normal cellular activities such as cell division, can then lead to cancer

Question 30

discuss gene expression in cells

Answer 30

all cells contain genes, though only certain genes are expressed in any one cell at any one time.
some genes are permanently expressed in all cells
while others are switched on only when needed