10.3 polygenic inheritance
- 1. 10.3 Polygenic Inheritance Topic 10 Genetics
- 2. Polygenic Inheritance 10.3.1 Define polygenic inheritance. 10.3.2 Explain that polygenic inheritance can contribute to continuous variation using two examples, one of which must be human skin colour.
- 3. Polygenic Inheritance So far, the characteristics we have studied have been controlled by one gene. Some characteristics are controlled by more than one gene. This is called Polygenic Inheritance. Examples of traits controlled by polygenic inheritance include: skin colour, eye colour, seed colour in wheat,
- 4. Polygenic Inheritance It is important not to confuse multiple alleles with polygenic inheritance. Blood type is an example of multiple alleles, whereby blood type is controlled by three possible alleles (IA , IB , i) all occurring at one locus. Polygenic inheritance involves many genes at several different loci.
- 5. Continuous vs Non-continuous Variation Variation is expressed by the different phenotypes for a characteristic. Variation can be: Continuous. Exhibits a wide range of phenotypes ranging from one extreme to the other. Discontinuous. Usually only has 2 forms. Polygenic Inheritance can contribute to continuous variation.
- 6. Human Skin Colour Human skin colour is a result of polygenic inheritance. Skin colour is controlled by 3 or 4 genes. Skin colour depends on the amount of a black pigment called melanin present. Each gene has alleles which promote melanin production and alleles which do not. Thus there is a wide range of phenotypes possible ranging from all alleles promoting melanin production (black Skin) to non alleles promoting melanin production (white skin).
- 7. Continuous Variation in Human Skin Colour as a Result of Polygenic Inheritance Ref: Yr12 Biology, Biozone
- 8. Seed Colour in Wheat Seed colour in wheat is also the result of polygenic inheritance. Seed colour is controlled by 3 genes, each on a different chromosome. Each gene has two alleles, coding for the production of a red pigment or not. Thus a seed can have up to 6 red alleles. Seed colour exhibits continuous variation, with seed colours ranging from dark red to white.
- 9. Ref: Advanced Biology, Roberts etal
- 10. Ref: Biology for the IB Diploma, Allott
- 11. IBO guide: 10.3.1 Define polygenic inheritance. 10.3.2 Explain that polygenic inheritance can contribute to continuous variation using two examples, one of which must be human skin colour.
- 12. IBO guide: Aim 8: This is one of the most obvious opportunities to develop the theme of parity of esteem for all humans. The selective advantage of dark skin to protect against ultraviolet light and light skin to allow vitamin D production could be mentioned. The correlation between skin colour and intensity of sunlight is clear, though the selective advantages of particular skin colours can now be overcome by the use of sun-block creams and vitamin D supplements.