Genetics

Question 0

Which genetic changes most likely lead to cancer?

Answer 0

Loss of Heterogeneity.

Question 1

What is an epigenetic alteration?

Answer 1

An epigenetic alteration is an enduring change in gene expression that doesn’t involve alteration of the DNA sequence.
Eg. Methylation of the promoter regions of genes leading to inactivation of the gene

Increasingly being recognised as “somatic” alterations in cancer.

Question 2

What is the difference between Allelic and Non-Allelic Heterogeneity?

Answer 2

Allelic
- lots of mutations in the ONE gene, eg. CFTR1 gene

Non-Allelic
- mutations in TWO different genes

Question 3

What is Imprinting?

Answer 3

Imprinted Alleles are SILENCED via DNA METHYLATION,

such that the gene expressed is only from the one parent who has the non-imprinted allele.

Question 4

What is Mosaicism?

Answer 4

Mosaicism is when an individual has 2 or more cell lines that differ in genotype, but are from a single zygote/chromosome.

Can be chromosomal or single gene disorders.

Eg.
Gonadal Mosaicism:
Only occurs in germ cells. There is a mix of normal and mutated germ cells.
Explains why some families have 2 or more children affected even when both parents are normal.
- Eg DMD, Tuberous Sclerosis

Somatic Mosaicism:
Cells with the mutation that is mixed in with normal cells. (Some tissues carry the mutation whereas others don’t)
- Eg Mosaic Down Syndrome, Turners