A phenotype is the trait expressed in an organism that is related to a genotype. For example, some peas are wrinkled and some are smooth. This is based on
Phenotypes - Wrinkled Peas, Smooth Peas
Let's assume that this trait is controlled by a single gene and smooth peas are dominant and wrinkled peas are recessive.
In this example, there are 2 alleles (copies of the gene). One from each parent.
We can call capital A the dominant and lower case a the recessive
The genotype is the combination of alleles for a given individual.
Genotypes - AA, Aa, aA, aa
We can relate genotype to phenotype as follows:
|
Genotype
|
Phenotype
|
|
AA
|
Smooth Peas
|
|
Aa
|
Smooth Peas
|
|
aA
|
Smooth Peas
|
|
aa
|
Wrinkled Peas
|
When a genotype contains 2 of the same alleles we call it homogenous. When there is one of each it is known as heterogeneous
In this situation notice that the only combination of alleles that will produce the wrinkled peas phenotype is the aa. This is because the capital A allele is dominant over the lower case a.