Bellringer Problems: PKU

Bellringer Problems: Huntington’s Disease

Bellringer Problems:CF

Non-Mendelian Genetics

Modifications to the expected Mendelian ratios…

For example – in snapdragons, cross a red flowered plant with a white flowered plant…

Mendel predicted you would end up with…

But he was wrong…You get all *pink* flowers!

Why?

R = red and r = white

Red x white Pink x Pink

Incomplete Dominance

Incomplete DominanceIntermediate phenotype in

heterozygotes…

It is a “blend” between the dominant and recessive forms of the gene

Sample ProblemIn horses, the dominant D allele allows

coat color to fully develop. The d allele dilutes, or weakens, coat color. When a chestnut (brown) horse is crossed with a cremello (nearly white) horse, their offspring are palominos (gold with white manes and tails)

Sample Problem ContinuedWhat is the genotype of…• A chestnut horse? ______________• A cremello horse? ______________• A palomino horse? ______________What would be the expected

phenotypic ratios of a cross between two palomino horses?

Another example from your dragons…

The case of the missing purebred…

Manx cats are born tailless. But if you cross two Manx cats you will never get 100% Manx kittens. Never ever ever.

Lethal Alleles

Lethal AllelesThe homozygous condition is lethal…

Sample ProblemAchondroplasia, a form of dwarfism, is

caused by the dominant allele A. Embryos with the genotype AA do not survive. Suppose that two people with achondroplasia get married and have children.

What phenotypic ratio would you observe in the couple’s children?

The case of the orange cows…

In cattle, red hair is dominant to white hair…but when you cross a red bull with a white cow, you get…

ROAN CATTLE

CodominanceDefinition:

Codominance• BOTH alleles are expressed at the same

time • Heterozygous = both phenotypes

expressed equally

R = red and R’ = white

Red x white Roan x Roan

Practice ProblemAndalusian chickens– Black feathers is codominant with white

feathers– Heterozygous = __________________________

FB = black and FW = white

Black x white FBFW x FBFW

It’s a guy thing, you wouldn’t understand…

Sex-linkedDefinition:

Sex-linkedPattern of inheritance for genes

located on X (sex) chromosome. Rarely on Y…

Sex-linked GenesExample: ColorblindnessXB, Xb, YGenotypes? Phenotypes?

PracticeColorblindness:Normal Male x Carrier Female

Genotypes Phenotypes

Sex-linked GenesExample: HemophiliaXH, Xh, YGenotypes? Phenotypes?

PracticeHemophilia:Hemophiliac Male x Carrier Female

Genotypes Phenotypes

Blood Types