Cancer Genetics - Inherited disease risk

Question 1

Retinoblastoma

Answer 1

Retinoblastoma (Rb) is a type of eye cancer that affects young children, mainly under the age of six. It develops in the cells of the retina.

Question 2

Wild type allele

Answer 2

The allele that encodes the phenotype most common in a particular natural population is known as the wild type allele.

Question 3

Are tumour suppressor genes dominant or recessive and why?

Answer 3

Recessive as both alleles must be mutated/lost for
cancer to develop.

But the “first hit” germline mutation
at the genotypic level is actually inherited in an
autosomal dominant fashion.

Question 4

Rb gene promotes development of what cancer?

Answer 4

Retinoblastoma

Question 5

How can mutant Rb genes be both dominant and recessive?

Answer 5

At the level of the whole organism mutant Rb allele is DOMINANT because an individual that inherits a defective Rb allele is almost certain to develop retinoblastoma.

At the level of the cell mutant Rb allele is RECESSIVE because a cell with one mutant and one normal Rb allele behaves normally.

Question 6

BRCA 1 gene is found where?

Answer 6

Chromosome 17

Question 7

BRCA 2 gene is found where?

Answer 7

Chromosome 13

Question 8

Explain complete vs incomplete penetrance.

Answer 8

Complete and incomplete or reduced penetrance: An allele is said to have complete penetrance if all individuals who have the disease-causing mutation have clinical symptoms of the disease. In incomplete or reduced penetrance, some individuals will not express the trait even though they carry the allele.