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“I’m XY and I Know It”: Sex Determination Systems 101

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X0 sex-determination system - Wikipedia

Not intercourse, though — more about how genetic sex is programmed during development. Sexual identity has been in the news often lately, and unsurprisingly so: the past few years have yielded sweeping reforms in civil rights, spurring new conflicts surrounding everything from age-old battles in gender equality to legislation enforcing anti-transgender bathrooms. Most multicellular organisms, humans included, use sexual reproduction to reproduce. Compared to asexual reproduction, in which cells can simply create carbon copies of themselves, sexual reproduction allows for the introduction of genetic diversity into a population. In most sexually reproducing organisms, there are two sexes — but the ways in which these sexes are determined and the ways in which they manifest vary greatly.
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XX/"XO" sex determination system in a population of Peruvian owl monkey, Aotus

Sex Determination is the process by which two sexes, male and female, become into being. It determines the development of the sexual organs of the organism. The presence or absence of the X chromosome in male gametes determines sex. Females are the homogametic sex XX. Males only have one chromosome X and are represented by XO - they act as the heterogametic sex.
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Insects harbor a tremendous diversity of sex determining mechanisms both within and between groups. For example, in some orders such as Hymenoptera, all members are haplodiploid, whereas Diptera contain species with homomorphic as well as male and female heterogametic sex chromosome systems or paternal genome elimination. We have established a large database on karyotypes and sex chromosomes in insects, containing information on over species covering 29 orders of insects. This database constitutes a unique starting point to report phylogenetic patterns on the distribution of sex determination mechanisms, sex chromosomes, and karyotypes among insects and allows us to test general theories on the evolutionary dynamics of karyotypes, sex chromosomes, and sex determination systems in a comparative framework.
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