Why D works. The Bat37 change is found in the polyp and nowhere else in the mouse, so it arose in a body (somatic) cell of the intestine during the mouse's life. Pups come from eggs and sperm, which carry only what the germ line carries, so none of them can inherit the change.

Why the others fail.

A (100%) treats the change as if both of the parent's copies of the marker carried it in every cell.
B (50%) is the chance a pup inherits the parent's Pms2 G allele, which is in every cell, including the germ line. The Bat37 change is not.
C (25%) applies a cross between two carriers, and the mate here is wild type.

Beat the test. A change found in a tumor but not in the same individual's normal tissue is somatic. Somatic changes aren't passed to offspring.

Take to test

somatic vs germ-line mutation

somatic: in a body cell, can start that person's tumor; germ line: in the gamete lineage, passed to offspring

Logic required: change in the polyp only (stem) → somatic → not in eggs or sperm → D.

Section Review

Results: Sample B/B passage

By passage

Questions