6.1 mutations

Question 1

what is a mutation?

Answer 1

a mutation is a random change to the genetic material of an organism - some mutations involve changes to the structure or number of chromosomes

Question 2

what is a gene mutation?

Answer 2

a gene mutation is a change to the DNA

Question 3

when do mutations occur?

Answer 3

mutations may occur spontaneously during DNA replication before cell division

Question 4

what are the two main classes of DNA mutation?

Answer 4

the two main classes of DNA mutation are:

• point/substitution mutation
• insertion or deletion (indel) mutation

Question 5

what is a point mutation?

Answer 5

a point mutation is when one base pair is substituted for another

Question 6

what is an insertion mutation?

Answer 6

an insertion mutation is when one more nucleotides are inserted into a length of DNA

Question 7

what is a deletion mutation?

Answer 7

a deletion mutation is when one more nucleotides are deleted from a length of DNA

Question 8

what do indel mutations cause?

Answer 8

indel mutations cause a frameshift

Question 9

what are the three types of point mutation?

Answer 9

the three types of point mutation are:

• silent mutations
• missense mutations
• nonsense mutations

Question 10

what is a silent mutation?

Answer 10

a silent mutation is where the base triplet still codes for the same amino acid

Question 11

what is a missense mutation?

Answer 11

a missense mutation is when a change to the base triplet leads to a change in the amino acid sequence in a protein

Question 12

what does a missense mutation have on the effect of the protein produced?

Answer 12

a missense mutation would lead to the alteration of the primary structure which leads to a change to the tertiary structure of the protein, altering its shape and preventing it from carrying out its usual function

Question 13

what does a change in the tertiary structure prevent the protein from doing?

Answer 13

a change in the tertiary structure prevents the protein from carrying out its usual function

Question 14

why does swapping one base with another have no effect on the protein produced?

Answer 14

swapping one base with another has no effect on the protein produced because each amino acid is coded for by more than one codon - this is referred to as the DNA code being degenerate

Question 15

what does it mean that the DNA code is degenerate?

Answer 15

the DNA code is a degenerate code which means that the majority of amino acids are coded for by more than one codon

Question 16

what is an example of a disorder caused by a missense mutation?

Answer 16

an example of a disorder caused by a missense mutation is sickle cell anaemia

Question 17

what is a nonsense mutation?

Answer 17

a nonsense mutation may alter a base triplet, so that it becomes a termination triplet

Question 18

what does a nonsense mutation result in?

Answer 18

a nonsense mutation result in a truncated protein that will not function

Question 19

which genetic disease is a result of a nonsense mutation?

Answer 19

the genetic disease Duchenne muscular dystrophy is a result of a nonsense mutation

Question 20

why will an indel mutation lead to a frameshift?

Answer 20

an indel mutation will lead to frameshift because the bases are read as triplets

Question 21

what happens when a base pair is inserted or deleted from a DNA sequence?

Answer 21

when a base pair is inserted or deleted from a DNA sequence it has a knock-on effect on all subsequent base triplets

Question 22

why is there a knock-on effect on all subsequent base triplets?

Answer 22

there is a knock-on effect on all subsequent base triplets because the code is non-overlapping

Question 23

what happens when the mRNA from a mutated gene is translated?

Answer 23

when the mRNA from a mutated gene is translated, the amino acid sequence will be altered as well as the tertiary structure

Question 24

what does inserting or deleting a whole base triplet result in?

Answer 24

inserting or deleting a whole base triplet results in the addition or loss of an amino acid

Question 25

what does inserting or deleting a whole base triplet not result in?

Answer 25

inserting or deleting a whole base triplet does not result in a frameshift

Question 26

what is Huntington disease a result of?

Answer 26

Huntington disease is a result of an expanding triple nucleotide repeat

Question 27

what do some genes contain?

Answer 27

some genes contain a repeating triplet such as -CAG CAG CAG-

Question 28

what is a repeating triplet known as?

Answer 28

a repeating triplet is known as an expanding triple nucleotide repeats

Question 29

in an expanding triplet nucleotide repeat, at which stage does the number of triplets increase?

Answer 29

in an expanding triplet nucleotide repeat, the number of triplets increase at meiosis and again from generation to generation

Question 30

what happens if the number of repeating CAG sequences goes above a certain critical number?

Answer 30

if the number of repeating CAG sequences goes above a certain critical number, then the person with that genotype will develop the symptoms of Huntington disease later in life

Question 31

when are genetic mutations beneficial?

Answer 31

genetic mutations are beneficial to organisms during natural selection (antibiotic resistance for bacteria)