[9.1] mutations

Question 1

how might gene mutations arise?

Answer 1

• during DNA replication when errors are made with the inclusion of new bases
• gene mutations occur spontaneously, but mutation rate is increased by mutagenic agents
• chemical mutagenic agents are called carcinogens

Question 2

what is the effect of a gene mutation?

Answer 2

• mutations can result in a different AA sequence in the encoded polypeptide
• they can be advantageous (variation), cancerous, or harmless

Question 3

examples of (chemical) mutagenic agents

Answer 3

• radiation: UV radiation, x-rays
• chemicals: cigarette smoke, barbecuing, benzoyl peroxide
• infectious agents: HPV, heliobacter pylori

Question 4

what is a substitution mutation?

Answer 4

when one base is swapped for another (ATGCCT -> ATTCCT)

Question 5

what is a deletion mutation?

Answer 5

when one or more bases are removed (ATGCCT -> ATCCT)

Question 6

what is an addition mutation?

Answer 6

when one or more bases are added
(GGCTA -> GGGCTA)

Question 7

what is an inversion mutation?

Answer 7

when a sequence of bases is reversed (AATTGCG -> TTAAGCG)

Question 8

what is a translocation mutation?

Answer 8

when a sequence of bases is moved from one location within the genome to another

Question 9

what is a duplication mutation?

Answer 9

when one or more bases are repeated (GTCAAG -> GTCAAAAG)

Question 10

what impact does a mutation have on the protein made?

Answer 10

• mutation has (eg.) removed a base and caused a frame shift
• from the point on the mutation, mRNA will be transcribed differently
• all amino acids after this point will now be in a different shape
• now the hydrogen/ionic/sulfur bonds within the protein are in different positions
• the protein then has a different shape and is non-functional (could be cancerous)

Question 11

are mutations still problems for introns?

Answer 11

• yes for addition or deletion (frame shift)
• no for substitution
  > substitution has the possibility to not create a different protein due to the degenerate code

Question 12

what is an example of a genetic disease caused by a gene mutation?

Answer 12

• sickle cell anaemia
• caused by a substitution of CTT to CAT (glutamine to valine)
• recessive
• if you have this allele you will be resistant to malaria so is often found in places where there is malaria

Question 13

what is an oncogene?

Answer 13

a gene that when mutated or expressed at high levels, helps turn a normal cell into a tumour cell

Question 14

how does the imbalance between two genes cause cancer?

Answer 14

• proto oncogenes stimulate cell division
• tumour suppressor genes inhibit cell division
• when the interaction between these 2 genes becomes unbalanced, cancer can result

Question 15

what are chromosome mutations?

Answer 15

changes in the structure or number of whole chromosomes

Question 16

what happens when there are changes in whole sets of chromosomes?

Answer 16

• occur when organisms have three or more sets of chromosomes rather than the usual two
• this condition is called polyploidy
• mostly occurs in plants

Question 17

what happens when there are changes in the individual number of chromosomes?

Answer 17

• sometimes individual homologous pairs of chromosomes fails to separate during meiosis
• this is known as non-disjunction and usually results in a gamete having either one more or one fewer chromosome
• example: down’s syndrome, where individuals have an additional chromosome 21