7'5 Polygenic Inheritance

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7.5 Polygenic Inheritance
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By the end of this lesson you should be able to

• Define discontinuous variation.
• Define continuous variation.
• Explain the difference between single-gene and
  polygenic inheritance.
• Describe the relationship between the number of
  genes controlling a characteristic and the number
  of phenotypes.
• Use a Punnett square to work out possible
  genotypes of offspring for polygenic inheritance.
• Give examples of polygenic inheritance in plants
  and animals.

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Types of Variation
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• Characteristics which fall into distinct
  categories are said to show discontinuous
  variation.
• Single-gene inheritance is where characteristics
  are controlled by the alleles of only one gene.

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• Characteristics which show a range of differences
  from one extreme to another are said to show
  continuous variation.
• Polygenic inheritance occurs when characteristics
  are controlled by the alleles of more than one
  gene.

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Example of Polygenic Inheritance
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Kernel colour in maize
R1 red, R2 red, r1 white, r2 white
P
Phenotype
Very dark red
White
Genotype
R1R1R2R2
r1r1r2r2
X
Gametes
All R1R2
All r1r2
F1
R1r1R2r2
Genotype
Phenotype
Medium red
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F1
R1r1R2r2
R1r1R2r2
Genotype
X
Medium red
Phenotype
Medium red
Gametes
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R1R1R2R2
R1R1R2r2
R1R1R2r2
R1r1R2R2
R1r1R2r2
r1r1R2R2
Genotypes?
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Phenotypes?
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• What effect does having a greater number of
  alleles have on the number of phenotypes for a
  characteristic?

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Comparing Single-gene and Polygenic Inheritance
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Copy and complete the table
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Examples of Inheritance
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Are you now able to?

• Define discontinuous variation.
• Define continuous variation.
• Explain the difference between single-gene and
  polygenic inheritance.
• Describe the relationship between the number of
  genes controlling a characteristic and the number
  of phenotypes.
• Use a Punnett square to work out possible
  genotypes of offspring for polygenic inheritance.
• Give examples of polygenic inheritance in plants
  and animals.