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 whitePink x Pink
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.
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 BOTH alleles are expressed at the same time Heterozygous = both phenotypes expressed equally
R = red and R’ = white Red x whiteRoan x Roan
Practice Problem Andalusian chickens – Black feathers is codominant with white feathers – Heterozygous = __________________________
F B = black and F W = white Black x whiteF B F W x F B F W
It’s a guy thing, you wouldn’t understand…
Sex-linked Pattern of inheritance for genes located on X (sex) chromosome. Rarely on Y…
Sex-linked Genes Example: ColorblindnessColorblindness X B, X b, Y Genotypes?Phenotypes?
Practice Colorblindness: Normal Male x Carrier Female GenotypesPhenotypes
Sex-linked Genes Example: Hemophilia X H, X h, Y Genotypes?Phenotypes?
Practice Hemophilia: Hemophiliac Male x Carrier Female GenotypesPhenotypes