Edexcel IGCSE Biology 3.22 Polygenic inheritance

Practise explaining why traits such as height show continuous variation when many genes affect one phenotype rather than a single allele pair.

Exam points

explain wider height variation in cattle or chickens by linking many genes to continuous variation
state that polygenic inheritance means more than one gene controls one phenotype

[Maximum number: 1]

Fur colour in rats is controlled by a gene with two alleles.

One allele codes for black fur colour. The other allele codes for agouti fur colour.
Several female rats with agouti coloured fur are mated with several male rats with black coloured fur.

All of the offspring have agouti coloured fur.

Scientists observed that genes that control fur colour in rats can affect rat behaviour, such as how tame they are.

Other genes that control the size of the adrenal glands and the production of neurotransmitters also affect rat behaviour.

Scientists also noticed that coat colour is associated with differences in anatomy and physiology, such as the size of the adrenal glands and the production of neurotransmitters.

State the name of the type of genetic control where many genes control one phenotype.

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3.22 Polygenic inheritance question 1