Transcript Non-Mendelian Genetics

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 Dominance
Intermediate phenotype in
heterozygotes…
It is a “blend” between the dominant and
recessive forms of the gene
Sample Problem
In 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 Continued
What 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 Alleles
The homozygous condition is lethal…
Sample Problem
Achondroplasia, 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
Codominance
Definition:
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 Problem
Andalusian chickens
– Black feathers is codominant with white feathers
– Heterozygous = __________________________
FB = black and FW = white
Black x white
F BF W x F BF W
It’s a guy thing, you wouldn’t
understand…
Sex-linked
Definition:
Sex-linked
Pattern of inheritance for genes located
on X (sex) chromosome. Rarely on Y…
Sex-linked Genes
Example: Colorblindness
XB, Xb, Y
Genotypes?
Phenotypes?
Practice
Colorblindness:
Normal Male x Carrier Female
Genotypes
Phenotypes
Sex-linked Genes
Example: Hemophilia
XH, Xh, Y
Genotypes?
Phenotypes?
Practice
Hemophilia:
Hemophiliac Male x Carrier Female
Genotypes
Phenotypes
Blood Types