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