Mutations

Question 1

Define mutations

Answer 1

A change in the quantity of DNA or the sequence of nucleotide bases in the DNA

Question 2

What causes mutations? What increases the frequency?

Answer 2

➣Incorrect pairing during DNA replication
➣Naturally at random and the rate at which genes mutate
➣Mutagenic agents increase the frequency, e.g. x-rays, gamma rays, chemicals like benzene

Question 3

What are the ways the nucleotides bases can be altered?

Answer 3

Substitution and deletion

Question 4

Describe substitution

Answer 4

Replacement of one or more bases by another base.

Question 5

What does substitution result in?

Answer 5

➣A new triple coding for a different amino acid in the polypeptide chain which could result in a non-functional protein
➣1 different amino acid in the chain but a functional protein
➣Same amino acid is coded for due to the degeneracy of the code, e.g. CGA and CGG both code for the same AA, so the polypeptide remains the same
➣The formation of a stop code which terminates the polypeptide chain so a non-functional protein is produced

Question 6

Describe deletion and its effect

Answer 6

➣The removal of one or more bases, which results in a frame shift: the alteration in the codons from the point of deletion
➣The sequence of amino acids is altered and protein is non-functional

Question 7

Describe chromosome mutations

Answer 7

A change in the structure of a whole chromosome

Question 8

When do chromosome mutations occur?

Answer 8

➣When an organism has 3 or more sets of chromosomes rather than 2. This is polyploidy and is mainly in plants.
➣There’s changes in the number of individual chromosomes if homologous pairs in chromosomes fail to separate in meiosis, this is non-disjunction. Results in a gametes having one more or less chromosome, resulting in offspring having it in all their cells. Down syndrome is the effect of an additional 21