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Past thoughts on genetic factors influencing aggression, specifically in regard to sex chromosomes, tended to seek answers from chromosomal abnormalities. [4] Four decades ago, the XYY genotype was (erroneously) believed by many to be correlated with aggression.
In the wake of the establishment of the normal number of human chromosomes, 47,XYY was the last of the common sex chromosome aneuploidies to be discovered, two years after the discoveries of 47,XXY, [27] 45,X [28] and 47,XXX [29] in 1959. Even the much less common 48,XXYY [30] had been discovered in 1960, a year before 47,XYY.
The two syndromes have a number of symptoms in common, such as tall stature (although the height increase in XYY appears greater than that in XYYY [1] [18]) and behavioural issues. One significant observed distinction is that while males with 47,XYY karyotypes usually have normal fertility, 48,XYYY appears associated with infertility or sterility.
48,XXYY syndrome is a condition related to the X and Y chromosomes (the sex chromosomes). People normally have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics. Females typically have two X chromosomes ...
In this system, the sex of an individual usually is determined by a pair of sex chromosomes. Typically, females have two of the same kind of sex chromosome (XX), and are called the homogametic sex. Males typically have two different kinds of sex chromosomes (XY), and are called the heterogametic sex. [1]
However, the experimental design had many flaws, including small sample sizes, biased sampling, and poor definition of the phenotype "aggression", resulted in the mischaracterization of XYY individuals as aggressive and violent criminals, which led the path for many biased studies on height-selected, institutionalised XYY individuals in the ...
In a normal situation, all the cells in an individual will have 46 chromosomes, with one being an X and one a Y or with two Xs. However, sometimes during the early copying processes of DNA replication and cell division, one chromosome can be lost. In 45,X/46,XY, most or all of the Y chromosome is lost in one of the newly created cells.
Most mammals, including humans, have an XY sex-determination system: the Y chromosome carries factors responsible for triggering male development. 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]