Genes are parts of our DNA sequence that carry information for the production of proteins. They are located in 23 pairs of human chromosomes. Chromosomes appear in pairs because we get one from our mother and one from our father. Thus, every person has two sets of chromosomes in their cells (except sex cells, which only have one set).
One variant of a given gene is called an allele. Two alleles can be identical or different. We all have the same genes; it’s just that some people have different versions (variations in DNA sequence).