The diagram displays the chromosomes present in a male.  There are two of each autosomal chromosome and two different sex chromosomes.  There are two copies of every autosomal gene and one copy of each sex-linked gene.  Because one of each type of chromosome came from each parent, there are likely to be different alleles present for many of the genes on the autosomes.  The alleles may be dominant, recessive, or co-dominant.  Dominant and co-dominant alleles produce observable traits when only one copy of the allele is present.  Recessive alleles only produce traits when no dominant alleles are also present.