DNA contains the genetic instructions for producing proteins through sequences of the bases adenine, thymine, guanine and cytosine. A gene is a unit of DNA that codes for a single protein, and alleles are variations of a particular gene that are always located in the same position on a chromosome, which contains multiple genes in wound DNA. Most chromosomes exist as homologous pairs, providing two copies of each gene.

1. Genetics Simplified
DNA: a molecule composed of the four bases Adenine, Thymine, Guanine and Cytosine. DNA provides the cell instructions on how to produce
proteins.
Proteins: complex molecules composed of amino acids. Proteins are built based on DNA sequences.
Gene: a unit of DNA located at a particular region of a chromosome that typically codes for one protein.
Allele: a variation of a particular gene. Regardless of what alleles we carry, they are always located at the same spot (locus) on a
chromosome.
Chromosome: A long strand of wound-up DNA containing many genes.
With the exception of the Y-chromosome, chromosomes come in matched sets (homologous chromosomes). So, we have two copies of each
chromosome and two copies of each genes (again, with the exception of the Y-Chromosome). In homologous chromosomes we may have
two of the same allele (homozygous) or two different alleles (heterozygous).