Mutation

Challenges to clear

• Work through all four cases correctly.
• Answer the calloused-hands case — the question Lamarck got wrong.

The task

Mutation is easy to define and easy to misunderstand. Think each case through.

What this lesson covers

• A gardener notices one branch of a rose bush bearing flowers of a completely different colour from the rest. The change appeared suddenly and the cuttings from that branch keep the new colour. What has happened? Best choice: A mutation — a sudden inheritable change in the genetic material — It appeared suddenly, was not present before, and is passed on to the next generation. That is exactly what a mutation is. Such a branch is called a bud sport.
• A man works for years without gloves and develops thickly calloused hands. Will his children be born with thicker skin on their palms? Best choice: No — a change to body cells acquired during life is not passed on — Only changes in the gametes can be inherited. Calluses are a change in somatic cells caused by use, and gametes are unaffected.
• Which of these is a recognised cause of mutation? Best choice: Radiation, certain chemicals, and errors during DNA replication — X-rays, gamma rays, ultraviolet light, mutagenic chemicals and copying mistakes during replication all alter the genetic material.
• Are mutations useful or harmful? Best choice: Most are harmful or neutral, but a few are useful — and those are the raw material of variation — A random change in a working set of instructions is far more likely to damage than improve. The rare advantageous ones are what natural selection can act on.

Hint

Two tests for a mutation: is it sudden, and is it inheritable? A change in body cells during life fails the second test.