bacterial and viral genetics

Question 1

Describe the three different

types of mutations

Answer 1

The three major types of mutations that arise are base substitutions, frameshift mutations and
transposable genetic elements (transposons).

Question 2

Explain the consequences of

mutagens on DNA.

Answer 2

mutagens :
Physical mutagens include heat, ultraviolet light and ionising radiation. Heat causes the deamination
of nucleotides while ultraviolet light induces the formation of pyrimidine dimers. Highly reactive hydroxyl
radicals are induced by ionising radiation. The hydroxyl radicals can either destroy the ring of the base or
cause single or double-stranded breaks in the DNA

chemical mutagens :
There are 3 classes of chemical mutagens: nucleotide -base analogues, frameshift mutagens and
DNA-reactive chemicals.
>Nucleotide-base analogues result in mispairing and DNA replication errors; for
example, 5-bromouracil can replace thymidine in DNA.
>Ethidium bromide or acridine derivatives which are flat, polycyclic molecules are examples of frameshift
mutagens. These molecules are inserted (intercalate) between the bases and stack with each other
thereby increasing the distance between bases and disrupting the sugar-phosphate backbone of DNA
>Nitrous acid and
alkylating agents are DNA-reactive chemicals which act directly on the DNA and change the chemical
structure of the base. The modified bases can either pair abnormally or not at all. The damage could cause
the removal of the base from the DNA backbone.

Question 3

explain the consequences of transposons

Answer 3

Transposons (aka jumping genes) are DNA sequences that can move around genomes of
prokaryotic or eukaryotic cells and will either create or reverse mutations.

Question 4

Differentiate between insertion

sequences and transposons

Answer 4

Insertion sequences are part of transposons (sequences of DNA that can move around to different positions within the genome of a single cell in a process called transposition), which use insertion sequences to insert into another or another part of the genome.

Question 5

Explain how viral mutants are

formed

Answer 5

Viruses are continuously changing as a result of genetic selection. They undergo subtle genetic changes through mutation and major genetic changes through recombination. Mutation occurs when an error is incorporated in the viral genome. Recombination occurs when coinfecting viruses exchange genetic information, creating a novel virus