In this variant of the XY system, females have two copies of the sex chromosome (XX) but males have only one (X0). The 0 denotes the absence of a second sex chromosome. Generally in this method, the sex is determined by amount of genes expressed across the two chromosomes. This system is observed in a number of insects, including the grasshoppers and crickets of order Orthoptera and in cockroaches (order Blattodea). A small number of mammals also lack a Y chromosome. These include the Amami spiny rat (Tokudaia osimensis) and the Tokunoshima spiny rat (Tokudaia tokunoshimensis) and Sorex araneus, a shrew species. Transcaucasian mole voles (Ellobius lutescens) also have a form of XO determination, in which both sexes lack a second sex chromosome. The mechanism of sex determination is not yet understood.
in this variant of the xy system females have two copies of the sex chromosome (xx) but males have only one (x0) the 0 denotes the absence of a second sex chromosome generally in this method the sex is determined by amount of genes expressed across the two chromosomes this system is observed in a number of insects including the grasshoppers and crickets of order orthoptera and in cockroaches (order blattodea) a small number of mammals also lack a y chromosome these include the amami spiny rat (tokudaia osimensis) and the tokunoshima spiny rat (tokudaia tokunoshimensis) and sorex araneus a shrew species transcaucasian mole voles (ellobius lutescens) also have a form of xo determination in which both sexes lack a second sex chromosome the mechanism of sex determination is not yet understood