The blue gene (Bl) is a diluting gene. It is known as an autosomal incomplete dominant gene. Chickens have 39 pairs of chromosomes. They have two categories of chromosomes known as sex chromosomes and autosomes. An autosome is simply defined as a chromosome that is not a sex chromosome. Genes are contained within these chromosomes. Each parent contributes one allele to form a particular gene in a diploid organism (birds are included). Incomplete dominance means that one allele is not completely expressed (or dominant) over the allele that it is paired with. This results in a phenotype that is a combination of both alleles. This explains why blue chicks produced in a blue, black and splash breeding pen are not all the exact same shade of blue. Some may be lighter in color and others may be darker in color, due to the incomplete dominance.