Multiple gene inheritance Revision Notes | GCSE OCR Foundation Biology

What this lesson covers

Understand that most characteristics are controlled by multiple genes rather than single genes, and appreciate the complexity of real inheritance patter...

• Explain how multiple genes interact to determine most characteristics
• Compare single gene inheritance with multiple gene inheritance patterns
• Analyse examples of polygenic traits in humans and other organisms
• Evaluate the role of environmental factors in polygenic inheritance

Key ideas to keep in view

Use this lesson to stay inside B5.1 Inheritance while connecting the detail back to the wider B5: Genes, inheritance and selection topic.

• B5: Genes, inheritance and selection
• B5.1 Inheritance
• GCSE OCR Foundation Biology

Lesson notes preview

Read the core explanations from Multiple gene inheritance before testing yourself from memory.

• You've learned about simple inheritance - brown eyes dominant over blue, or blood groups with clear patterns. But look around your classroom. Why isn't everyone either very tall or very short? Why do people have every shade of skin colour imaginable?
• Most characteristics aren't controlled by just one gene. Height, skin colour, intelligence, and even your risk of heart disease involve multiple genes working together. This is called polygenic inheritance, and it's actually the norm, not the exception.
• The inheritance pattern where multiple genes contribute to a single characteristic, creating continuous variation rather than distinct categories.
• Trap: Many students think all inheritance follows simple dominant/recessive patterns. Actually, most traits show continuous variation because multiple genes are involved, each adding a small effect.
• Think of height like a recipe where multiple ingredients each add a little bit. Gene A might add 2cm, Gene B adds 1cm, Gene C adds 3cm. The more 'tall' alleles you inherit, the taller you become.
• This creates what we call continuous variation - a smooth range of values rather than distinct categories. Instead of 'tall' or 'short', you get every height in between.
• Variation that shows a range of phenotypes between two extremes, typically forming a bell-shaped (normal) distribution when plotted.
• Single-gene traits produce distinct categories (for example ABO blood groups: A, B, AB, O). Polygenic traits produce a continuous range (for example height from 150 cm upward).
• Let's examine skin colour - one of the best-understood examples of polygenic inheritance. At least 6 different genes contribute to melanin production, each with multiple alleles.
• Human height: Over 700 genetic variants identified, each contributing small amountsIntelligence (IQ): Thousands of genes involved, plus major environmental factorsBlood pressure: Multiple genes affecting heart function, kidney function, and blood vessel structure

Continue through the topic

Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.