The ploidy of a cell or organism is the number of complete sets of chromosomes it contains. A diploid cell has two complete sets of chromosomes, while a haploid cell has only one complete set. The nucleus of a cell contains the chromosomes, which are made up of DNA. DNA is the genetic material that determines the traits of an organism. The larger the nucleus, the more DNA it contains, and the more genes it can express. This is why larger nuclei are often associated with greater complexity and diversity of organisms.