Topic 10.3 Polygenic Inheritance
Name:
1. Define polygenic inheritance.
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2. Distinguish between polygenic inheritance and multiple alleles.
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3. List one human and one plant example of polygenic inheritance.
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4. Polygenic inheritance gives rise to continuous variation within a population.
Explain what this means, using skin colour as an example.
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5. Compare the advantages and disadvantages of light and dark skin.
Light Skin
Cold Climate
Dark Skin
Lack of exposure to sunlight can
result in vitamin D deficiency
Hot Climate
6. State precautionary measures that could be taken by:
a. Pale-skinned people to avoid the dangers of hot climates?
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b. Dark-skinned people to reduce the disadvantage of a cold climate?
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7. Assume that two genes (A and B) are responsible for inheritance of skin colour, with two alleles each and that they
are unlinked. The dominant alleles code for melanin production.
a. Calculate the number of possible genotypes.
b. Apply the possible genotypes to the range of phenotypes below:
aabb
Aabb
PRACTICAL TASK
Polygenic inheritance occurs when many genes interact to produce a single trait. The genes may be on the same
chromosome or on different chromosomes, and each gene may have two or more alleles. Each allele contributes a small,
but equal, portion to the trait being expressed. The result is that the phenotypes usually show a continuous range of
variability from the minimum value of the trait to the maximum value.
In humans, height is controlled for more than two genes. In this activity, you are going to measure the height of the
students in the class in centimeters, and record the information on a data table. Then you are going to make a graph with
you results. If it is true that more than two genes control height in humans, then your graph should have the shape of a bell.
INSTRUCTIONS
1. Measure the height of the students in centimeters.
2. Record the information in a data table.
3. Make a graph with the information gathered.
Data Table: Height of students in my school
8. Using a punnet grid, explain why it is possible for children to have skin which is darker or lighter than both parents.
Mother genotype:
Father genotype:
AB
i.
Ab
aB
ab
AB
Ab
aB
ab
Outcome and explanation.
9. A characteristic is controlled by two unlinked genes with two alleles.
Deduce the number of possible genotypes and phenotypes.
10. A characteristic is controlled by three genes with two alleles each. Calculate the number of genotypes possible in a
cross between a homozygous recessive father and a homozygous dominant mother.
11. Wheat kernel colour is controlled by three unlinked genes (A, B and C). The dominant alleles code for production of
a red pigment. Deduce the phenotype ratio expected in a test cross with a wheat plant that is homozygous
dominant for A, heterozygous for B and homozygous recessive for C. Show your working.
PRACTICE QUESTION