Post on 18-Jan-2016
Polygenetic inheritance
Polygenetic inheritanceObjectives
Outline what polygenetic inheritance is.
Outcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in
variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
10.3.1 Define Polygenic inheritancePolygenic Inheritance – When a single trait is influenced by many genes.
Each allele of a polygenic character often contributes only a small amount to the over all phenotype.
This makes studying the individual alleles difficult.
In addition environmental effects smooth out the genotypic variation to give continuous distribution curves.
Polygenetic inheritanceOutcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
Polygenetic inheritanceOutcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
Polygenetic inheritanceOutcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
Polygenetic inheritanceOutcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
Polygenetic inheritanceOutcomes
3: Describe an example of polygenetic inheritance.
5: Explain why polygenetic inheritance arises.
7: Evaluate the importance of polygenetic characteristics in variation and evolution.
Key terms: polygenetic inheritance, continuous, variation.
Polygenic Inheritance of skin color
aabbcc AABBCC
At least four loci and possibly more genes are involved.
Example 3 loci: each has two possible alleles: A,a B,b C,c, each capital allele adds one unit of darkness each lower case allele adds nothing
Parents with
intermediate tone
Offspring can have tone darker or lighter than either parent
0 1 52 63 4Number of ‘darker’ alleles
Polygenic Inheritance of skin color
Questions1. Which human trait shows a pattern of polygenetic inheritance?A. ABO blood typeB. Sickle cell anaemiaC. Skin colourD. Co-dominant alleles
2. Why is it sometimes difficult to identify how certain characteristics are inherited in humans.A. Most genes are linked.B. Rates of mutation are high.C. The inheritance may be polygenic.E. The environment varies so little.
3. Describe the effects of polygenic inheritance using two specific examples. (5)
Key terms: polygenetic inheritance, continuous, variation.
Questions1. C2. C3. More than one gene controls / affects one characteristic;Reject more than 2 allelescan cause continuous variation / many different possible phenotypes;eg skin colour / other valid example;
allele of each gene promotes melanin production or not / other validexample;eg grain colour in wheat / other valid example;
allele of each gene promotes pigment production or not / other validexample; 5 maxIf first or second example is incorrect do not accept third or subsequent examples.
Key terms: polygenetic inheritance, continuous, variation.