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? 2. Slightly Above Average? 3. tad shorter than extremely tall? AaBbcc AABBcc aABBCC

What will the children look like? There are 4 possibilities. Fill in the chart. AABBCC x AaBbcc Child’s allelle (letter) combination What is the child’s height? AABBCcVery tall AaBBCcAbove average AABbCcAbove average AaBbCcAverage Tall FatherShorter Mother

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 ABLOOD TYPE B BLOOD TYPE ABBLOOD TYPE O

Multiple Alleles Example: Blood Type in Humans –There are 3 alleles floating in the population: I A, I B, i; but a person will only get 2 of them. –The I A & I B 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? I A i IBIBIBIB IA IBIA IB IA IBIA IB IB iIB i IB iIB 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? i ii i IAiIAiIA IBIA IB i i IB iIB i IBIB IAIA

Sex-Linked Inheritance Sex is determined by chromosomes THINK! – Who determines the sex of the baby, mom or dad? XX XY X XYXY 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 F 1 generation look like? –All red eyed flies XrYXrY X R X r X R Y X R X r X R Y X R X R

Sex-Linked Problems THINK! – Next, Morgan took a red-eyed female from the F1 generation and a red-eyed male from the F 1 generation and mated them. What did the Punnett Square look like? THINK! - What did the F 2 generation look like? –Only the males had the recessive trait of white eyes X R X r XRYXRY X R X R X R X r X R Y X r 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 Color Blind Test bend.com/colorblind/Ishihara.asp