Genetics of Sexual Differentiation and Sexually Dimorphic Behaviors

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Research suggests, however, that in a few births per thousand some individuals will be born with a single sex chromosome 45X or 45Y sex monosomies and some with three or more sex chromosomes 47XXX, 47XYY or 47XXY, etc. In addition, some males are born 46XX due to the translocation of a tiny section of the sex determining region of the Y chromosome. Similarly some females are also born 46XY due to mutations in the Y chromosome. Clearly, there are not only females who are XX and males who are XY, but rather, there is a range of chromosome complements, hormone balances, and phenotypic variations that determine sex.

The biological differences between men and women result from two processes: sex determination and differentiation. The process of biological sex differentiation development of a given sex involves many genetically regulated, hierarchical developmental steps. The Y chromosome acts as a dominant inducer of male phenotype and individuals having four X chromosomes and one Y chromosome 49XXXXY are phenotypically male.

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In the absence of both a Y chromosome and the influence of a testis-determining factor TDF , ovaries develop. Gender, typically described in terms of masculinity and femininity, is a social construction that varies across different cultures and over time. It is apparent, then, that different cultures have taken different approaches to creating gender distinctions, with more or less recognition of fluidity and complexity of gender. Typical sexual development is the result of numerous genes, and mutation in any of these genes can result in partial or complete failure of sex differentiation.

These include mutations or structural anomalies of the SRY region on the Y chromosome resulting in XY gonadal dysgenesis, XX males, or XY females; defects of androgen biosynthesis or androgen receptors, and others.

The issues of gender assignment, gender verification testing, and legal definitions of gender are especially pertinent to a discussion on the ELSI of gender and genetics. These practices, however, are misnomers as they actually refer to biological sex and not gender. Such a discrepancy is highlighted by the existence of intersex individuals whose psychosexual development and gender sometimes do not match the biological sex assigned to them as infants.

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Chromosomes are the structures that carry genes which in turn transmit hereditary characteristics from parents to offspring. Humans have 23 pairs of chromosomes, one half of each pair inherited from each parent.


The Y chromosome is small, carries few genes, and has abundant repetitive sequence, while the X chromosome is more autosome-like in form and content. Aneuploidy is the condition of having less than monosomy or more than polysomy the normal diploid number of chromosomes. Prenatal diagnosis of SCA is increasing because of the widespread use of these technologies. The high frequency of individuals with SCA is due to the fact that their effects are generally not as severe as autosomal abnormalities and are rarely lethal.

Indeed, most cases of SCA are compatible with normal life expectancy and often go undiagnosed. This disorder, also referred to as monosomy X 45X occurs in individuals that have one X chromosome, no Y chromosome, and are phenotypically female. Although 45X is a frequent chromosomal anomaly, Turner syndrome is rare with a live-birth frequency of , 23 as only 1 in 40 affected zygotes develops to term.

In some instances of Turner syndrome, there is slight mental retardation. Women with three X chromosomes 47XXX experience normal development of sexual traits and are fertile. Affected individuals are usually taller than average and have slender builds. The frequency of women obtaining an extra X chromosome is approximately There is no severe phenotype associated with three X chromosomes in women. As a result of this hormone imbalance, affected males have incompletely developed secondary male sex characteristics.

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Men inheriting an additional Y chromosome are usually taller than average and are prone to acne because they produce higher than average levels of testosterone. Affected males are typically fertile and many are unaware that they have a chromosomal abnormality. The frequency of males born with an additional Y chromosome is approximately Congenital adrenal hyperplasia CAH is an inherited autosomal recessive condition that can affect both boys and girls. It is the most common cause of intersexuality in females with 46XX, where untreated girls develop an outwardly male appearance.

This disorder, also called adrenogenital syndrome AGS , results from a genetically caused deficiency of cortisol, a steroid hormone produced by the adrenal cortex. Submit Feedback.

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