Chromosomes contain DNA and proteins. Genes within chromosomes hold the code for building and maintaining an organism. Genes are located at specific positions on chromosomes. Diploid cells contain two copies of each chromosome - one from each parent. The interactions between gene copies give rise to traits like dominance. Chromosomes exist in two states - before and after DNA replication. Genes have fixed locations on chromosomes. Chromosomes package DNA through histone proteins that DNA winds around.