6.1.3 - Somatic v Germline mutations

Question 1

Somatic mutations

Answer 1

• Occurs due to replication errors prior to mitsosis, often spontaneously during the S phase of the cell cycle
• If these errors are not repaired during proof-reading in G2, the mutation will permanently change the genetic information contained in the cell
• When a mutated cell continues to divide by mitosis, the error is replicated each time and passed on to cells in successive divisions
• The mutation is confined to that tissue due to cell specialisation, as mutated cells in one tissue will not form parts of a different tissue.
• Phenotypic difference e.g. pigmented cells in carcinoma, or a tumour
• Somatic mutations cannot be passed down to offspring, and results in mosaicism or affects only a patch of the organism

Question 2

Germline mutations

Answer 2

• Germline mutations occur in the sexual reproductive cells that give rise to gametes
• These mutations are passed on to offspring because when a zygote is formed from the syngamy of a mutated cell and a normal cell, the zygote inherits the mutations of its parent and the mutation is replicated in every cell of the embryo as it divides and grows
• Germline mutations affect the entire organism
• Half of the affected organism’s gametes will carry the mutation, so it can be inherited