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XY complete gonadal dysgenesis, also known as Swyer syndrome, is a type of defect hypogonadism in a person whose karyotype is 46,XY. Though they typically have normal vulvas , [ 1 ] the person has underdeveloped gonads, fibrous tissue termed " streak gonads ", and if left untreated, will not experience puberty .
In the absence of a Y chromosome, the fetus will undergo female development. This is because of the presence of the sex-determining region of the Y chromosome, also known as the SRY gene. [5] Thus, male mammals typically have an X and a Y chromosome (XY), while female mammals typically have two X chromosomes (XX).
XX gonadal dysgenesis is a type of female hypogonadism in which the ovaries do not function to induce puberty in a person assigned female at birth, whose karyotype is 46,XX. [1] Individuals with XX gonadal dysgenesis have normal-appearing external genitalia as well as Müllerian structures (e.g., cervix, vagina, uterus).
46,XX/46,XY chimeric or mosaic is associated with a wide spectrum of different physical presentations, with cases ranging from having a completely normal male or female phenotype [7] [8] [9] to some cases having ovotesticular syndrome. Due to this variation, genetic testing is the only way to reliably make a diagnosis.
45,X/46,XY mosaicism, also known as X0/XY mosaicism and mixed gonadal dysgenesis, [1] is a mutation of sex development in humans associated with sex chromosome aneuploidy and mosaicism of the Y chromosome. It is a fairly rare chromosomal disorder at birth, with an estimated incidence rate of about 1 in 15,000 live births. [2]
Externally, the most sexually dimorphic portions of the human body are the chest, the lower half of the face, and the area between the waist and the knees. [7] Males weigh more than females on average. [8] On average, males are taller than females by about 7% (12 cm). [9] [10]
Ovotesticular disorder: patients having both ovarian and testicular tissue. In some cases the ovarian tissue is functional. XY, Sex reversal: patients with female phenotypes where duplication in the Xp21.2 region of the X chromosome that contains the NR0B1 gene is associated with XY sex reversal.
Whilst XY sex determination is the most familiar, since it is the system that humans use, there are a range of alternative systems found in nature. The inverse of the XY system (called ZW to distinguish it) is used in birds and many insects, in which it is the females that are heterogametic (ZW), while males are homogametic (ZZ). [18]