Complete dominance – the dominant has the same effect whether present in one or two copies
Cross a pea plant with purple flowers (homozygous) and a pea plant with white flowers homozygous.
What are the genotypes and phenotypes for the 4 possible combinations?
Codominance – both alleles are expressed in heterozygous individuals
A mother with blood type AB marries a man with blood type O. What are the different blood types that
their children may have?
Incomplete dominance – heterozygotes express a phenotype that falls between the two parental
phenotypes
Cross a snapdragon with red flowers with a snapdragon with pink flowers. What are the genotypes and
phenotypes of the four possible combinations?
Test cross – mating between an individual with unknown genotype and a homozygous recessive to
determine the genotype of the unknown individual
Case of complete dominance
B = black
b = brown
You have recently bought a black Labradoodle from a kennel across town. The man who sold it to you
told you that both the mother and the father both had black fur. He seems a little sketchy and you want
to find out if this is true. Possible genotypes for your dog are _____ or ______. In order to determine
the unknown genotype of your dog you set up a test cross with your neighbor’s Labradoodle who is
homozygous recessive. What will be the results if your Labradoodle is heterozygous or homozygous?
This is called a test cross.
Heterozygous
Homozygous