Other Patterns of Inheritance

SECTION 11.3

Beyond Dominant and Recessive Alleles

u  Exceptions to Mendel’s Principles

u  Incomplete Dominance: some alleles are neither dominant or recessive.

u The heterozygous phenotype lies somewhere between the two homozygous phenotypes.

Beyond Dominant and Recessive Alleles u  Exceptions to

Mendel’s Principles

u Co-dominance: phenotypes of both alleles is clearly expressed.

Beyond Dominant and Recessive Alleles u  Exceptions to Mendel’s

Principles

u  Multiple Alleles: genes which exist in MANY different forms. More than two alleles.

Practice u  A cross between a blue

blahblah bird (B) & a white blahblah (W) bird produces offspring that are silver (BW).  The color of blahblah birds is determined by just two alleles. What would the genotypic and phenotypic ratios be for a cross between two silver blahblah birds?

u  Cattle can be red (RR = all red hairs), white (WW = all white hairs), or roan (RW = red & white hairs together).  What would be the genotypic and phenotypic ratios of a cross between a roan bull and red cow?

Practice

u  Coat color in rabbits is inherited as a series of multiple alleles. In the case of rabbits, there are four alleles and each one is expressed with a different phenotype. Suppose you cross a chinchilla rabbit (cchch) with a dark gray rabbit (Cch). What are the possible offspring and genotypic/phenotypic ratios?

Practice

phenotype allele pattern of inheritance

dark gray coat C dominant to all other alleles

chinchilla cch dominant to Himilayan and to white

Himilayan ch dominant to white white c recessive