Remember that cells have pairs of chromosomes (Homologues). Each chromosome in a pair contains genes for the same characteristics. Thus the individuals above each have two chromosomes which each hold a gene to determine Hair Color. The genes on the chromosomes are called alleles. Many alleles exhibit a dominant/ recessive relationship. In other words, if a person has a chromosome with a dominant gene and a chromosome with a recessive gene, then the dominant gene will decide that characteristic.

Genotype - the gene types of an organism; the alleles for a certain characteristic: Genotypes can be described several ways. They can be listed e.g. BB or Bb, or described as in Heterozygous or Homozygous Dominant etc.

Phenotype - the way an organism's genes express themselves (Biochemical manifestation of Genotype); It is often thought of as a physical characteristic, either short, tall, Blonde Hair, etc. However, many genes specifiy characteristics that can not be seen.