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Complex Inheritance Polygenic Inheritance • Many genes working together to control a single phenotype • Just break down the word: – “poly” means many – “genic” means genes • Height and skin color are traits that are controlled by more than one gene Polygenic Inheritance • Here’s how it works. Let’s say 3 genes control height – A, B, & C are “tall” alleles each contributing a unit of tallness – a, b, & c are “short” alleles each contributing a unit of shortness Polygenic Inheritance • THINK! – What is the phenotype for each of the genotypes below? • AABBCC = Extremely Tall • aabbcc = Extremely Short • AaBbCc = Average Height THINK! - Can you think of other genetic combinations that would still turn out to be average height? Let’s List them. Extend: Can you figure out the Genotype (Letters) for each person? 1. Slightly Below Average? AaBbcc 3. tad shorter than extremely tall? aABBCC 2. Slightly Above Average? AABBcc What will the children look like? There are 4 possibilities. Fill in the chart. AABBCC x Tall Father AaBbcc Shorter Mother Child’s allelle (letter) combination What is the child’s height? AABBCc Very tall AaBBCc AABbCc AaBbCc Above average Above average Average Polygenic Inheritance • THINK! – Can you think of more examples for polygenic inheritance? – HINT: Think of traits in which the phenotype has a broad range of variation. • Weight • Hair Color • Eye Color What are the Human Blood Types? BLOOD TYPE A BLOOD TYPE AB BLOOD TYPE B BLOOD TYPE O Multiple Alleles • Example: Blood Type in Humans – There are 3 alleles floating in the population: IA, IB, i; but a person will only get 2 of them. – The IA & IB alleles are said to be codominant. – Codominant means both alleles are expressed. Thus, the person has type AB blood. Blood Type in Humans Blood Type Problems • THINK! – Amy is heterozygous for type A blood. Jim is homozygous for type B blood. What is the chance they will have a child with type B blood? IB IB IA i IA IB IB i IA IB IB i Blood Type Problems • THINK! – Jill is blood type O. She has two older brothers. One has type A blood and one has type B blood. What are the genotypes of the parents? IB i IA IA IB IAi i IB i ii Sex-Linked Inheritance • Sex is determined by chromosomes X X X XX XX Y XY XY • THINK! – Who determines the sex of the baby, mom or dad? Dad Sex-Linked Inheritance • Any gene located on the X chromosome is considered to be sexlinked. • Sex-linked inheritance was discovered by Thomas Hunt Morgan in fruit flies. Sex-Linked Problems • THINK! – Morgan took a pure redeyed female and crossed it with a pure white-eyed male. What did the Punnett Square look like? • THINK! – What did the F1 generation look like? – All red eyed flies XR XR Xr XR Xr XR Xr Y XR Y XR Y Sex-Linked Problems • THINK! – Next, Morgan took a red-eyed female from the F1 generation and a red-eyed male from the F1 generation and mated them. What did the Punnett Square look like? • THINK! - What did the F2 generation look like? – Only the males had the recessive trait of white eyes XR Xr XR XR XR XR Xr Y XR Y Xr Y Sex-Linked Traits • In sex linked traits: – Females need 2 copies of a recessive allele to show the trait – Males only need 1 copy of a recessive allele to show the trait – Mothers pass sex-linked traits to their sons via the X chromosome • Other sex-linked traits include: – Colorblindness – Male pattern baldness – Hemophilia (blood clotting disorder) Examples of Vision of the Color Blind http://www.vischeck.com/examples/ Color Blind Test http://www.toledobend.com/colorblind/Ishihara.asp