Multifactorial systems involve rearrangements of sex chromosomes and autosomes. "C. elegans" has five pairs of autosomes and one pair of sex chromosomes. Sex is instead determined by the ratio of X chromosomes to autosomes. "Drosophila" flies have both X and Y chromosomes, as well as autosomes. The other 22 chromosomes (the autosomes) are the same for both sexes. In haplodiploidy, males receive one half of the chromosomes that females receive, including autosomes. All chromosomes are acrocentric except for the first pair of autosomes, which are submetacentric. It has one pair of large submetacentric autosomes and 27 acrocentric autosomal pairs. The number of autosomes in all karyotypes was 58. Closely linked genes on autosomes called "supergenes" are often responsible for the latter. Accessory gland proteins which are male biased and shows positive selection reside entirely on autosomes. The first 22 pairs are called autosomes. The autosomes include 31 pairs of sub-graded subacrocentrics, but one only pair of metacentrics. The autosomes contain the rest of the genetic hereditary information. The autosomes consist of five pairs of small to medium-sized metacentrics and submetacentrics.