1. POLYGENIC INHERITANCE
AHL Topic 10.3
IB Biology
Miss Werba

2. DIHYBRID CROSSES & GENE LINKAGE POLYGENIC INHERITANCE
AHL TOPIC 10 – GENETICS
10.1 MEIOSIS
10.2
DIHYBRID CROSSES & GENE LINKAGE
10.3
POLYGENIC INHERITANCE
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3. THINGS TO COVER Definition of polygenic inheritance
Continuous variation
Two examples:
Skin colour in humans
Seed colour in wheat
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4. POLYGENIC INHERITANCE Command term = DEFINE
10.3.1
POLYGENIC INHERITANCE Command term = DEFINE
A single characteristic controlled by multiple genes
Gives rise to continuous variation in a phenotype.
eg.
skin colour in humans
seed colour in wheat
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5. POLYGENIC INHERITANCE Command term = DEFINE
10.3.1
POLYGENIC INHERITANCE Command term = DEFINE
Other examples:
obesity
eye colour
susceptibility to diseases such as heart disease, cancer, mental illness
The Autism Spectrum
It is suspected that multiple gene interactions and environmental factors play a role in inheritance here.
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6. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Human skin colour:
controlled by 3 or 4 genes
skin colour depends on the melanin concentration of the skin (a black pigment)
each gene has alleles which promote melanin production and alleles which do not.
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7. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Human skin colour:
Thus there is a wide range of phenotypes possible
Range from:
all alleles promoting melanin production
all alleles impeding melanin production
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8. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Human skin colour:
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9. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Human skin colour:
lusion_of_skin_color?language=en
Nina Jablonski is an anthropologist and author of Skin: A Natural History, a close look at human skin’s many remarkable traits.
Nina Jablonski says that differing skin colors are simply our bodies' adaptation to varied climates and levels of UV exposure. Charles Darwin disagreed with this theory, but she explains, that's because he did not have access to NASA.
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11. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Human skin colour:
Advantages of dark skin in hot climates?
UV protection
Protection against skin damage and cancer
Dark skinned people in cold climates / low-sunlit areas may need vitamin D supplements
Advantages of pale skin in cold climates?
Increased vitamin D production in low-sunlight conditions
Increased immune protection
Pale skinned people in hot climates / high-sunlit areas need sunscreen!
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12. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Wheat seed colour:
controlled by 3 genes, each on different chromosomes
each gene has two alleles, coding for the production of a red pigment
exhibits continuous variation, with seed colours ranging from dark red to white
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13. 10.3.2
POLYGENIC INHERITANCE & CONTINUOUS VARIATION Command term = EXPLAIN using EXAMPLES
Wheat seed colour:
Ref: Biology for the IB Diploma, Allott
Ref: Advanced Biology, Roberts etal
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14. Sample questions Q1. What is polygenic inheritance?
A character that is controlled by two or more genes
A character that is controlled by more than two copies of a gene
Inheriting more than two alleles of a gene
Inheriting a linked group of genes
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15. Sample questions Q2. Define the term polygenic inheritance. [1]
Explain, using a named example, how polygenic inheritance gives rise to continuous variation. [2]
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16. Sample questions
A1. A
A2.
Character affected / influenced /defined / determined / controlled by two or more genes 1
human skin colour can vary from pale to very dark / amount of melanin varies; skin colour/melanin controlled by (alleles from) at least 3 / several genes; alleles are co-dominant / incomplete dominance; many different possible combinations of alleles; skin colour controlled by cumulative effect/combination of genes/alleles; 2 Award the above marking points for any other valid example.
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