State that most phenotypic features are the result of multiple genes…

The idea

This statement asks you to recognise that most observable characteristics (phenotypes) arise from the combined effect of many genes working together, not from one gene acting alone. A phenotype is the visible or measurable feature of an organism, such as height, skin colour or mass. Single-gene inheritance, where one gene with two alleles controls a feature, is the exception rather than the rule; examples include simple cases such as the ability to roll the tongue. Most features, including human height and body mass, show continuous variation because many genes each contribute a small effect, and the environment also plays a part. In a multiple-choice question, look for the option that says most phenotypes are controlled by several genes, and reject options claiming that a single gene controls most features or that environment alone determines them.

What earns the marks

• Selects the option stating that most phenotypic features are controlled by multiple genes acting together.
• Rejects the option claiming that a single gene with two alleles controls most phenotypic features.
• Recognises that features such as human height show continuous variation because many genes contribute.
• Distinguishes multiple-gene inheritance from the rarer single-gene cases such as tongue rolling.

Common mistakes and how to put them right

• Chooses the option that one gene controls most features.

  Put it right by recalling that single-gene inheritance is the exception.

• Assumes the environment alone determines most phenotypes.

  Put it right by stating that multiple genes contribute alongside environmental effects.

• Treats continuous variation as proof of a single gene.

  Put it right by linking continuous variation to many genes each adding a small effect.

Exam tips

• Read every option before choosing, because distractors often swap 'single gene' and 'multiple genes'.
• Link the correct option to a familiar example such as human height to confirm your choice.
• Eliminate options that claim environment alone or one gene alone controls most features.