Objectives
Outcomes
Outline what polygenetic
inheritance is.
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 inheritance
Polygenic 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.
Skin colour video
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.
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.
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.
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.
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.
Polygenic Inheritance of skin color
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
aabbcc
AABBCC
Offspring can have tone darker or lighter than either parent
Polygenic Inheritance of skin color
0
1
2
3
4
5
Number of ‘darker’ alleles
6
1.
A.
B.
C.
D.
Which human trait shows a pattern of polygenetic inheritance?
ABO blood type
Sickle cell anaemia
Skin colour
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.
D.
The environment varies so little.
3.
Describe the effects of polygenic inheritance using two specific
examples. (5)
Key terms: polygenetic inheritance, continuous, variation.
1. C
2. C
3. More than one gene controls / affects one characteristic;
Reject more than 2 alleles
can cause continuous variation / many different possible phenotypes;
eg skin colour / other valid example;
allele of each gene promotes melanin production or not / other valid
example;
eg grain colour in wheat / other valid example;
allele of each gene promotes pigment production or not / other valid
example;
5 max
If first or second example is incorrect do not accept third or subsequent
examples.
Key terms: polygenetic inheritance, continuous, variation.