Mutations and Variation

Question 1

Mutation:

Answer 1

Change in the sequence of bases in DNA.

Question 2

What is the effect of mutations?

Answer 2

• Protein synthesis can be disrupted if the mutation occurs within the gene.

Question 3

Different types of mutation?

Answer 3

• Substitution
• Deletion
• Insertion

Question 4

Substitution:

Answer 4

• Change in single nucleotide changes the codon.
• If codon codes for different amino acid this will change primary structure of the protein.
• The position and involvement of the amino acid group in R group interactions will determine the impact.
• However, new codon can still code for same amino acids, so synthesised protein does not change.

Question 5

Insertion:

Answer 5

• Leads to frameshift mutation.
• The triplet code means that sequences of bases are transcribed consecutively in non-overlapping groups of three.
• This means that every successive codon from point of mutation is changed.

Question 6

Deletion:

Answer 6

• Frame shift mutation
• The triplet code means that sequences of bases are transcribed consecutively in non-overlapping groups of three.
• This means that every successive codon from point of mutation is changed.

Question 7

When does insertion / deletion not have an effect on protein functioning?

Answer 7

• if 3 are inserted / deleted

Question 8

If mutation has no effect?

Answer 8

• No effect on phenotype of an organism because normally functioning proteins are still synthesised.

Question 9

If mutation damages?

Answer 9

• Phenotype of an organism is negatively changes because proteins are no longer synthesised or those synthesised are non-functional.

Question 10

If mutation is beneficial?

Answer 10

• Rarely a protein synthesised can be beneficial and results in a new / useful characteristic in phenotype.
• Eg. mutation in protein on cell surface membranes that HIV can not bind and enter cells.

Question 11

Causes of mutations:

Answer 11

• Spontaneous during DNA replication
• Rate of mutations is increased by mutagens.

Question 12

Mutagen?

Answer 12

• Chemical, physical or biological agent that causes mutation.

Question 13

Loss of a purine base (depurination) or pyrimidine base (depyrimidination)?

Answer 13

• Spontaneous
• Can lead to insertion through complementary base pairs.

Question 14

Free radicals?

Answer 14

• Oxidising agents that effect structures of nucleotides.
• Disrupt base pairing during DNA replication.
• Antioxidants (Vitamins A, C, E) are known anticarcinogens because they negate effect of free radicals.

Question 15

Main physical mutagens?

Answer 15

• ionizing radiations (x-rays)

Question 16

Main chemical mutagens?

Answer 16

• Deaminating agents

Question 17

Main biological agents?

Answer 17

• Alkylating agents
• Base analogs
• Viruses

Question 18

Silent mutations:

Answer 18

• Do not change any proteins / activity of proteins.
• Have no effect on phenotype of an organism.
• Occur in non-coding regions of DNA (introns) or in code.
• Can change primary structure without changing overall structure / function of proteins synthesised.

Question 19

Nonsense mutations:

Answer 19

• Stop codon.
• Protein is shortened and non-functional.
• Negative / harmful effect on phenotype.

Question 20

Missense mutations:

Answer 20

• Incorporation of incorrect amino acid(s).
• Result depends on the role of amino acid in structure and function of protein.
• Could be silent, beneficial or harmful.
• Includes conservative and non-conservative mutations.

Question 21

Conservative mutation:

Answer 21

• New amino acid has similar properties to the amino acid being coded for. Effect is less severe.

Question 22

Non-conservative mutation:

Answer 22

• New amino acid has different properties.
• More likely to have an effect on protein structure and may cause disease.

Question 23

Beneficial mutations: lactose

Answer 23

• Ability to digest lactose. This is found more in European communities that farmed cattle and East Africa.
• Prevents the development of osteoporosis and starvation during famine.

Question 24

Chromosome mutations: types

Answer 24

• Deletion
• Duplication
• Translocation
• Inversion

Question 25

Chromosome mutations?

Answer 25

- Caused by mutagens and normally occur in meiosis.

Question 26

Chromosome deletion:

Answer 26

A section of chromosome breaks off and is lost within the cell

Question 27

Chromosome duplication:

Answer 27

Sections get duplicated on a chromosome

Question 28

Chromosome translocation:

Answer 28

A section of one chromosome breaks off and joins another non-homologous chromosome

Question 29

Inversion:

Answer 29

A section of chromosome breaks off, is reversed, and then joins back onto the chromosome.