Molecular Pathology

Question 0

Give examples of

1) Mutation in coding region
2) Mutation affecting splicing
3) Mutation in promotor
4) deletion

Answer 0

1) cystic fibrosis, haemophilia
2) waadenburg syndrome
3) beta thalassemia
4) alpha thalassemia

Question 1

What are the 5 main recessive mutations

What do they produce (molecularly)

Answer 1

• coding region (exon) - affects translation of mRNA - can create a stop codon (truncated protein), insertion (abnormal protein) or destroy a critical amino acid (inactive protein)
• small insertion or deletion - affects the triplet reading frame
• splicing mutation - affects translation as frame contains an intron, could add a stop codon or add extra amino acid
• promotor mutation - no transcription
• gene deletion - no transcription (null mutation)

Question 2

What are the 3 extents of dominance and give a brief explanation of each.

Answer 2

Complete dominance - the phenotype is indistinguishable between homozygous or heterozygous - expression of normal gene product from one allele is sufficient to produce a normal phenotype.

Co dominance - both alleles of a gene are expressed independently of each other but do not interfere with each other (eg blood groups)

Partial dominance - the heterozygous genotype is insufficient - not enough normal gene product is expressed

Question 3

What is poisonous product and give an example

Answer 3

Dominant allele interferes with the activity of the normal allele

Eg methemoglobinaemia
Or osteogenesis imperfecta

Question 4

What are the 2 types of inappropriate expression?

Answer 4

Ecchronic expression - expressed at the wrong time

Ectopic - expressed in the wrong tissue