DNA mutations + genetic testing

Question 1

list some types of gene variations

Answer 1

Deletion
Duplication
Splice site variants
mis-sense variant
Non sense
Expansion of trinucleotide repeats
Anticipation
DNA damage
DNA repair issues

Question 2

Describe variation: Deletion

Answer 2

2 types = in frame and out of frame

in frame = one codon removed so only one amino acid is lost. Reading frame is not changed

out of frame = sequence shifts meaning reading frame of the gene is changed.

Question 3

Describe mis sense and non sense variation

Answer 3

Mis sense = A single nucleotide change results in a codon coding for a different amino acid. This can result in a non functional protein or can have no effect (degenerative nature of the genetic code).

None sense = A single nucleotide change that produces a premature stop codon. This results in an incomplete/non-functional protein.

Question 4

what is a Single Nucleotide Polymorphisms (SNP)

Answer 4

A single nucleotide substitution in DNA resulting in variation amongst a population.
E.g. sickle cell anaemia or cystic fibrosis
Can affect recognition/promoter/termination sequences to change the length of proteins

Question 5

List 3 features of the genetic code.

Answer 5

non overlapping
degenerative
universal

Question 6

describe ALLELIC HETEROGENEITY

Answer 6

Lots of different variants in one gene (cf)

Question 7

describe LOCUS HETEROGENEITY

Answer 7

Variants in different genes give the same clinical condition e.g. hypertrophic cardiomyopathy

Question 8

Dominant variants manifest the disease phenotype in the ______zygous state i.e. the condition occurs if there is one variant and one normal allele

Recessive variants only manifest the disease in the ______zygous state i.e. there have to be variants in both alleles. The majority of pathogenic variants are recessive.

Answer 8

hetro
homo

Question 9

what are the reasons to do a genetic test

Answer 9

Patient has signs and symptoms suggesting a particular diagnosis

genetic test will confirm a clinical diagnosis

Question 10

what different types of genetic testing would be conducted in clinical genetics

Answer 10

Diagnostic testing
Carrier testing
Predictive testing
Prenatal tests

Question 11

what type of tests are usually not offered in clinical genetics but in private or a forensic lab

Answer 11

Paternity tests
Genetic finger printing

Question 12

Discuss some of the roles of genetic testing

Answer 12

To confirm a clinical diagnosis

To give information about prognosis

To inform management

Allow pre-symptomatic/predictive testing in close relatives

Carrier testing

To give accurate recurrence risks

Prenatal diagnosis