Part I: Genetic Material
Lesson 3: DNA's Role in Determining Your Traits

Interestingly, genes were known to have allelic variation long before any DNA sequences were determined.  This is because some traits were known to vary according to rules of gene inheritance, such as the color of petals in the pea plant, as shown in the graphic on the right. 

Geneticists often use the terms "genotype" and "phenotype" when referring to alleles and traits. 

Genotype is defined as the alleles present in an individual's genome.

Phenotype is defined as the traits present in an individual.