Mendel’s pea plants had either purple or white flowers. this means that the plants

A gene is a section of a chromosome that typically contains the code for a particular protein, in this case, for flower color. An allele is one of two or more alternative forms of a gene. In this example, there are two alternative forms of the gene for flower color. The presence of two alternative forms implies there must be two alleles of the gene. 

nucleic acid molecules are incredibly complex, containing the code that guarantees the four different nucleotide units comprise dna, the nucleic acid of interest to the genealogist. and one of four nitrogen-containing molecules called nucleotides