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Polygenic inheritance is where multiple genes contribute to a single characteristic, creating continuous variation. Free notes and 12 questions answered.
Multiple gene inheritance is part of Reproduction in GCSE AQA Higher Biology.
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Polygenic inheritance is where multiple genes contribute to a single characteristic, creating continuous variation. Free notes and 12 questions answered.
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Use this lesson to stay inside Reproduction while connecting the detail back to the wider Inheritance, variation and evolution topic.
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.
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.
The key difference from single-gene inheritance:
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.
Worked example: Skin Colour Inheritance Model
If skin colour is controlled by 3 genes (A, B, C), each with two alleles, how many different skin tones are possible?
Answer: 7 basic categories from 3 genes, but hundreds of tones from 6+ genes in reality
Other clear examples include:
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
Here's where it gets really interesting. Your genes set the potential, but environment determines how much of that potential you reach. This is especially important for polygenic traits.
Take height again. Your genes might give you the potential to be 180cm tall, but poor nutrition during childhood could limit you to 170cm. Good nutrition might help you reach your full genetic potential.
This gene-environment interaction explains why:
• Identical twins can have different heights if raised in different conditions• Average height has increased over generations due to better nutrition• Some genetic diseases only appear under certain environmental triggers
Exam questions on polygenic inheritance often test your ability to distinguish between single-gene and multiple-gene patterns. Here's how to tackle them successfully.
Command word focus: 'Explain' questions want you to link cause and effect. For polygenic traits, always mention that multiple genes each contribute small effects that add up.
Common mistake: Students often confuse polygenic inheritance with codominance. Remember - codominance involves one gene with multiple alleles (like ABO blood groups), while polygenic involves multiple genes affecting one trait.
Polygenic traits show a spectrum because each contributing allele adds a small effect. The final phenotype reflects the combined contribution of many alleles plus environmental influences. In exam responses, describe both genetics and environment to explain why populations display continuous distributions rather than sharply separated groups.
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Continuous variation is variation that shows a range of phenotypes between two extremes, typically forming a bell-shaped (normal) distribution when plotted. It happens when multiple genes each add a small effect, such as in human height.
Polygenic inheritance is the inheritance pattern where multiple genes contribute to a single characteristic, creating continuous variation rather than distinct categories. Height, skin colour and blood pressure are examples, with each gene adding a small effect.
Phenotypic plasticity is the ability of a genotype to produce different phenotypes in response to different environmental conditions. It explains why identical twins raised in different conditions can have different heights.
Examples of polygenic traits are human height, with over 700 genetic variants; intelligence (IQ), involving thousands of genes and environmental factors; skin colour; and blood pressure, affected by genes for heart, kidney and blood vessel function.
Single-gene traits produce distinct categories, such as the ABO blood groups A, B, AB and O, while polygenic traits, controlled by multiple genes, produce a continuous range, such as height from 150 cm upward. Most characteristics are polygenic.
Genes set the potential for height, but environment determines how much of it is reached. Genes might give the potential to be 180cm tall, but poor nutrition in childhood could limit growth to 170cm, which is why average height has increased over generations with better nutrition.
If skin colour were controlled by 3 genes, each with a 'light' and 'dark' allele, there would be 6 alleles, ranging from 0 to 6 'dark' alleles, giving 7 categories. In reality at least 6 genes are involved, producing hundreds of tones and continuous variation.
Polygenic inheritance involves multiple genes affecting one trait, while codominance involves one gene with multiple alleles, such as ABO blood groups. Confusing the two is a common mistake.
Identical twins can have different heights if raised in different conditions, because environment affects how much of the genetic potential is reached. Height is a polygenic trait, and factors such as nutrition affect the final height.
Over 700 genetic variants affecting human height have been identified, each contributing a small amount. The more 'tall' alleles inherited, the taller a person can become, creating continuous variation.
Continuous variation typically forms a bell-shaped (normal) distribution when plotted, showing a range of phenotypes between two extremes. Polygenic traits such as height produce this smooth range rather than distinct categories.
At least 6 different genes contribute to melanin production in skin colour, each with multiple alleles. This gives hundreds of possible skin tones, explaining the continuous variation seen in human skin colour.