Session 9

Question 0

Predict and explain the effect that different mutations may have e.g. silent mutation, missense mutation, nonsense mutation, frame shift mutation

Answer 0

Silent - does not alter amino acid
Missense mutation - codes for a different amino acid
Nonsense mutation - codes for a stop codon
Frameshift mutation - addition or deletion of nucleotides not in multiples of 3

Question 1

Describe the different types of mutational changes e.g. point mutation, insertion, deletion

Answer 1

Point mutation - a change of a single nucleotide in a nucleic acid sequence (transition - purine –> purine, transversion - purine –> pyrimidine)
Insertion - addition of one or more nucleotides
Deletion - removal of one or more nucleotides

Question 2

Describe how spontaneous and induced mutations may occur

Answer 2

Spontaneous - random mistake

Induced - by a mutagen

Question 3

Describe the genetic link between mutation and mutant phenotype and explain how some mutations can be inherited

Answer 3

A mutation is a source of genetic variation
A mutation causes a mutant phenotype which is a phenotype which differs from the common or wild-type phenotype in the population
A mutation in a gene causes a mutant allele which can be passed on to offspring (inherited)

Question 4

Describe the process and role of DNA repair

Answer 4

Mismatch repair (post replication process) - an erroneously inserted nucleotide is recognised and replaced with the correct nucleotide
(Base/nucleotide) Excision repair - repair single stranded DNA damage caused by external agents (chemical mutagens, UV) or endogenous factors (ROS)
Double strand break (DSB) repair - both DNA strands are broken which can cause chromosome rearrangements

Question 5

Explain the relationship between DNA damage and cancer

Answer 5

Rate of DNA damage > rate of repair = diseased cell

Failure to repair DNA can cause disease (cancer, senescence, apoptosis)

Question 6

Provide an overview of the different genetic tests available for the detection of mutations in genes

Answer 6

Multiplex PCR-based test

SSCP (Single Strand Conformation Polymorphism)

Question 7

Show an appreciation of the ethical issues associated with genetic testing

Answer 7

Pre-natal diagnostic tests:
Amniocentesis - 15-20 weeks gestation, ultrasound guidance, cells must be recovered and may need culturing for 2 weeks, 0.5-1.0% risk of miscarriage
Chorion villus biopsy - 10-13 weeks gestation, ultrasound guidance, trans-cervical or trans-abdominal, foetal villi must be separated from maternal tissue, 2% risk of miscarriage
(Foetal DNA in mother’s blood)