POLYGENIC INHERITANCE AHL Topic 10 3 IB Biology

POLYGENIC INHERITANCE AHL Topic 10. 3 IB Biology Miss Werba

AHL TOPIC 10 – GENETICS 10. 1 MEIOSIS 10. 3 10. 2 DIHYBRID CROSSES & GENE LINKAGE POLYGENIC INHERITANCE J WERBA – IB BIOLOGY 2

THINGS TO COVER �Definition of polygenic inheritance �Continuous variation �Two examples: ◦ Skin colour in humans ◦ Seed colour in wheat J WERBA – IB BIOLOGY 3

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 J WERBA – IB BIOLOGY 4

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. J WERBA – IB BIOLOGY 5

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 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. J WERBA – IB BIOLOGY 6

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 Command term = EXPLAIN using EXAMPLES Human skin colour: � Thus there is a wide range of phenotypes possible � Range from: ◦ alleles promoting melanin production ◦ alleles impeding melanin production J WERBA – IB BIOLOGY 7

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 Command term = EXPLAIN using EXAMPLES Human skin colour: J WERBA – IB BIOLOGY 8

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 Command term = EXPLAIN using EXAMPLES Human skin colour: http: //www. ted. com/talks/nina_jablonski_breaks_the_i llusion_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. J WERBA – IB BIOLOGY 9

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 Command term = EXPLAIN using EXAMPLES Human skin colour: � Advantages of dark skin in hot climates? ◦ UV protection ◦ Protection against skin damage and cancer Ø 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 Ø Pale skinned people in hot climates / high-sunlit areas need sunscreen! J WERBA – IB BIOLOGY 11

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 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 J WERBA – IB BIOLOGY 12

POLYGENIC INHERITANCE & CONTINUOUS VARIATION 10. 3. 2 Command term = EXPLAIN using EXAMPLES Wheat seed colour: Ref: Biology for the IB Diploma, Allott Ref: Advanced Biology, Roberts etal J WERBA – IB BIOLOGY 13

Sample questions Q 1. What is polygenic inheritance? A character that is controlled by two or more genes b) A character that is controlled by more than two copies of a gene c) Inheriting more than two alleles of a gene d) Inheriting a linked group of genes a) J WERBA – IB BIOLOGY 14

Sample questions Q 2. a) Define the term polygenic inheritance. [1] b) Explain, using a named example, how polygenic inheritance gives rise to continuous variation. [2] J WERBA – IB BIOLOGY 15

Sample questions � A 1. A A 2. a) b) 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. J WERBA – IB BIOLOGY 16