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 = aabbcc = AaBbCc = Extremely Tall Extremely Short 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

AABBCc Very tall AaBBCc Above average AABbCc AaBbCc Average What will the children look like? There are 4 possibilities. Fill in the chart. AABBCC x AaBbcc Tall Father Shorter Mother Child’s allelle (letter) combination What is the child’s height? AABBCc Very tall AaBBCc Above average AABbCc AaBbCc 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 B BLOOD TYPE AB 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 IA i IB IA IB IB i IA IB IB i 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 IA IB IB i IA IB IB i

Blood Type Problems i IB IA IA IB IAi i IB i i i 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? IA IA IB IAi i IB i i i

Sex-Linked Inheritance Sex is determined by chromosomes THINK! – Who determines the sex of the baby, mom or dad? X X X Y XX XX XY XY Dad

Sex-Linked Inheritance Any gene located on the X chromosome is considered to be sex-linked. Sex-linked inheritance was discovered by Thomas Hunt Morgan in fruit flies.

Sex-Linked Problems THINK! – Morgan took a pure red-eyed 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 Y XR Xr XR Xr XR Y XR Y

Sex-Linked Problems XR Xr XR Y XR Xr XR XR XR Y Xr Y 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 Y XR Xr XR XR 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 – Ishihara Test