Chromosomes can be thought of as analogous to different colored pairs of socks. Each sock represents a single chromatid, a pair of socks represents sister chromatids and different colored socks represent other chromosomes.
Chromosomes exist as either a single chromatid or a pair of sister chromatids. Sister chromatids carry identical genetic information. During a type of cell division called meiosis, chromosomes also pair with homologs to form a homologous pair of chromosomes. Homologous chromosomes contain similar genetic information, but are not identical. While homologs contain the same set of genes, they may not contain the same version of genes or the same alleles.