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<p>of the platypus.</p>

<p><big> XX/X0 sex chromosomes </big></p>
<p>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 <a href="page.php?w=Orthoptera">Orthoptera</a> and in cockroaches (order <a href="page.php?w=cockroach">Blattodea</a>).</p><p>
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