Topic 4.3 Genetic Diversity

Question 1

What is a gene mutation?

Answer 1

● A change in the base sequence of DNA (on chromosomes)
● Can arise spontaneously during DNA replication (interphase)

Question 2

Examples of gene mutation

Answer 2

base deletion
or substitution

Question 3

What is a mutagenic agent?

Answer 3

A factor that increases rate of gene mutation, eg. ultraviolet (UV) light or alpha particles.

Question 4

Explain how a mutation can lead to the production of
a non-functional protein or enzyme

Answer 4

Changes sequence of base triplets in DNA (in a gene) so changes sequence of codons on mRNA
So changes sequence of amino acids in the polypeptide
So changes position of hydrogen / ionic / disulphide bonds (between amino acids)
So changes protein tertiary structure (shape) of protein
Enzymes- active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form

Question 5

Explain the possible effects of a substitution mutation

Answer 5

Base / nucleotide in DNA replaced by a different base / nucleotide
This changes one triplet so changes one mRNA codon
So one amino acid in polypeptide changes
● Tertiary structure may change if position of hydrogen / ionic
/ disulphide bonds change
OR amino acid doesn’t change
● Due to degenerate nature of genetic code (triplet could
code for same amino acid) OR if mutation is in an intron

Question 6

Explain the possible effects of a deletion mutation

Answer 6

One nucleotide / base removed from DNA sequence
Changes sequence of DNA triplets from point of mutation (frameshift)
Changes sequence of mRNA codons after point of mutation
Changes sequence of amino acids in primary structure of polypeptide
Changes position of hydrogen / ionic / disulphide bonds in tertiary
structure of protein
Changes tertiary structure / shape of protein

Question 8

What do nonesense mutations change?

Answer 8

Change the last base

Question 9

What do mis sense mutations change ?

Answer 9

Changing first or second base

Question 10

What is a nonesense mutations?

Answer 10

Results in a stop codon

Thus the polypeptide production would stop prematurely.

Question 11

What is mis sense mutation?

Answer 11

Causes a different amino acid to be coded for
Effect depends on function of amino acids

Question 12

What is a silent mutation?

Answer 12

Substitutes base still codes for same amino acid
There is no effect.
This is due to degenerate code.

Question 13

What do deletion mutations cause?

Answer 13

Deletion ,mutations cause frame shifts. All subsequent codons are altered. If this is near the start of a gene . It will have devastating effects

Question 14

What are the causes of mutation?

Answer 14

-all genes have a normal mutation rate cause by spontaneous errors during DNA replication
-mutagens speed up mutation rate
>high energy radiation
> chemicals alter DNA structure

Question 15

How do mutations in chromosomes arise ?

Answer 15

● Spontaneously by chromosome non-disjunction during meiosis
● Homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis
● So some gametes have an extra copy (n+1) of a particular chromosome and others have none (n-1)