Chromosome 1 is the largest human chromosome, made up of around 249 million nucleotide base pairs and representing approximately 8% of the entire DNA content. It is likely to contain 2,000 to 2,100 genes that provide instructions for making proteins, which perform a variety of different functions in the body. Some of the diseases associated with chromosome 1 include hearing loss, Alzheimers disease, glaucoma, and breast cancer. Genetic mutations of the chromosome have been linked to more than 350 human diseases, and structural alterations of the chromosome are believed to contribute to a variety of mental retardation syndromes. Changes in the number or structure of chromosome 1 can have a variety of effects, including delayed growth and development, distinctive facial features, birth defects, and other health problems.