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D1.3.6—Consequences in germ vs. somatic cells

Germ-line mutations can be inherited, whereas somatic mutations affect body-cell descendants and may contribute to disease in one individual only.

Syllabus
First assessment 2025
Objective
D1.3.6
Level
HL

Germline and Somatic Mutations Have Different Reach

A mutation in a germline cell can enter gametes and be inherited, while a somatic mutation remains in the affected body lineage unless special reproduction transfers it.

Cell lineage determines who receives the altered DNA. Germline changes can affect offspring; somatic changes can produce a mosaic tissue or disease in one individual.

Classify impact by checking: cell lineage; whether gametes carry the change; individuals or tissues affected.

A mutation in a skin cell can expand into a patch of altered cells but is usually not passed to a child.

‘Somatic’ does not mean harmless; it can strongly affect the individual even without inheritance.

Consequences in germ vs. somatic cells

Assessment in practice

1–3 marks
How it is assessed

This objective is assessed through multiple choice, commonly using Distinguish.

Command terms

Distinguish

What earns marks

Build the answer around this relationship: Only germ-line mutations can normally be passed to offspring.

Watch for

Saying any mutation can automatically be inherited regardless of cell type.

Representative question

Question 1

[Maximum number: 1]

A mutation in which type of cell could be inherited?

A

Beta cell in the pancreas

B

T-cell in the lymph

C

Sperm cell in the testis

D

Skeletal muscle cell in the diaphragm

Core Mutation Effects

Gene mutations are changes in the base sequence of DNA; main types are substitution, insertion, deletion, and duplication. Base substitutions can create SNPs and change codons; degeneracy can make substitutions silent, missense, or nonsense. Insertions or deletions not in multiples of three cause frameshifts that alter downstream codons and often disrupt protein function. Mutations can arise from replication errors, repair errors, or chromosome damage; mutagens include chemicals, ionizing radiation, and ultraviolet radiation. Mutations occur randomly with respect to organism need or advantage; mutation rate varies with DNA sequence, gene expression, repair, and mutagen exposure. Germ-line mutations can be inherited by offspring; somatic mutations affect only descendant body cells and can contribute to cancer. Mutation is the original source of new alleles and genetic variation; many are neutral or harmful, but variation supplies material for natural selection.

Concept essentials

  • Only germ-line mutations can normally be passed to offspring.
  • Somatic mutations affect body cells and their descendant cells.
  • Somatic mutations can contribute to cancer without being inherited by children.
  • Germ-line gene therapy raises heritable-change concerns.
ConceptIB Biology HL