Module 6 Lesson 6 - 3
Completion requirements
Lesson 6 — Polygenic Traits
Continuous Trait
Polygenic traits can involve the interaction of more than just two genes. These are too complex to predict and analyze, but in a general sense they are not too difficult to understand. Basically, the more genes involved in producing a single trait,
the greater the variety of possible phenotypes.
This means that, when multiple genes are influencing phenotypes such as height or weight, a range of variation occurs because of cumulative effects of various genes that affect the height or weight of an individual.
Read more about polygenic traits and continuous phenotypes in your textbook on pages 605 to 607.
Sometimes, the expression of an allele can be affected by the environment. For example, the fur pigment gene of arctic foxes is expressed only when the temperature is cold. During the winter months, the fur pigment gene is deactivated and the fur colour is white. During the summer months, the fur of arctic foxes turns into reddish brown.
Himalayan rabbits and Siamese cats have similar heat sensitive genes for the fur colour. In this case, the black pigment gene is deactivated when the temperature is higher than 33℃. At the extremities such as ear, nose, feet, and tail, where the body temperature can be lower than 33℃, the pigment gene is active and turns the fur black.
This means that, when multiple genes are influencing phenotypes such as height or weight, a range of variation occurs because of cumulative effects of various genes that affect the height or weight of an individual.
Read more about polygenic traits and continuous phenotypes in your textbook on pages 605 to 607.
Environmental Effect
Read pages 608 - 609
© Getty Images
© Getty Images
Sometimes, the expression of an allele can be affected by the environment. For example, the fur pigment gene of arctic foxes is expressed only when the temperature is cold. During the winter months, the fur pigment gene is deactivated and the fur colour is white. During the summer months, the fur of arctic foxes turns into reddish brown.
Himalayan rabbits and Siamese cats have similar heat sensitive genes for the fur colour. In this case, the black pigment gene is deactivated when the temperature is higher than 33℃. At the extremities such as ear, nose, feet, and tail, where the body temperature can be lower than 33℃, the pigment gene is active and turns the fur black.
Watch and Listen
Watch the following video on more inheritance patterns and environmental influences.
©Alberta Education. Alternate Patterns of Inheritance: The Potential for Diversity (19:26-28:50); Series 27. LearnAlberta.ca
Answer the following questions for your own understanding.
- How many phenotypes are there for rabbit fur coloration?
- How many genes are involved determining rabbit fur colours?
- How many genes are involved in determining human skin colour? What else affects human skin colour?
- Define or explain the following patterns of inheritance:
- epistasis
- the effect of the environment
- Is height in humans determined only by our genes?
- How does temperature affect coat colour in rabbits?
- There are four phenotypes: normal, chinchilla, Himalayan, and albino.
- One gene is involved in rabbit fur coloration.
- More than 100 genes are involved in producing human skin colour. Exposure to sunlight also affects the skin colour.
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- Epistasis occurs when one gene masks the expression of another gene.
- The expression of an allele can be affected by the environment, such as by temperature.
- The height of humans can also be affected by diet.
- In rabbits, when temperature is low, the coat colour is white. When temperature is higher, the coat colour turns brown.