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Chapter 10

Chapter 10

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University of Toronto Scarborough
Janelle Leboutillier

Chapter 10Sexual BehaviourSEXUAL DEVELOPMENT Aristotle argued that sex of the child resulted from temperature of semenhot semen male coolfemale We now know Aristotle is retarded and that the mother provides an X chromosome and father determines the offsprings sex by providing either an X or a Y chromosome The Fetus is undifferentiated in sexwithout exposure to male hormones all babies would be born with outwardly female physical appearance and behaviour Sex Chromosome AbnormalitiesIn a minority of cases variation in the sex chromosomes occurTheres no viable record of an organism hat has a single Y chromosome Turner Syndrome XOsingle x chromosomefirst described by Henry Turner it occurs in 1 out of 2500 births from turner syndrome we learned that a single X chromosome carries sufficient genetic material to produce an individual who is quite normal in many waysthe lack of a second sex chromosome has an impact on fertility growth hormone production and is associated with higher risk of diabetes osteoporosis and cardiovascular disease they have normal female external genitalia but the ovaries develop abnormally currently unidentified regions on the X chromosome and responsible for the development of ovaries and having a single X chromosome interferes with this process in most cases the ovaries do not produce either ova or normal levels of female hormones and this leads to infertility When the x chromosome I missing in some but not all cells or only a portion of the second X is missing woman may be fertilesome women with turner syndrome are relatively short average 48 and have increased skin folds a the neck intelligence is normal but specific deficits in spatial relationships and memory can occurHuman growth hormone female hormone replacement therapy and assisted reproductive technologies are used to address the issues of height hormone production and fertilityKlinefelter syndrome XXYfirst identified by Harry Klinefeltermost common genetic abnormalities related to the sex chromosomesoccurs in 179 out of 1000 malebirths they are male but experience reduced fertility and require hormone treatment at puberty to promote the development of secondary male sex characteristics and inhibit female characteristics such as breast development other symptoms are due t having an extra X chromosome due to the interference with the process of Xinactivationin which one x chromosome in each female cell is randomly silencednormal intelligence may have mild cognitive difficulties and social awkwardness these cognitive difficulties usually take the form of delayed and reduced verbal skills left handedness is most common among males with this syndrome than in the general male population which suggests that it might affect brain lateralization XYY genotype first reported by Sandberg Koepf Ishiara and Hauschka1 out of 1000 male births the physical and behavioural correlates are subtle and generally do not prompt parents to seek postnatal genetic analysis boys are usually within typical limits although leaner and taller suffer from acne and have a higher risk for minor physical abnormalities of the eye elbow and chest IQ slightly below average relative to males with XYfertile but at greater risk to produce sperm with sex chromosome abnormalities The Relationship between XYY genotype and likelihood of antisocial behaviour is mixedan initial report suggested that XYY was over represented in prisonsStudies showed that XYY men showed significantly higher anti social behaviours but their crimes were property rather than violent Further analysis showed that criminal and antisocial behaviour was more closely associated with lower intelligence than with an atypical genotype Down Syndrome3 copies of chromosome 21IN a large study of more than 13000 newborns over a 13 year period Nielsen and Wohlert found that none of the children with 3 sex chromosomes were mentally retarded and that all were in regular public school There were no increases in criminal activity mental disorders or physical disorders relative to the population with typical sex chromosomes However significant abnormalities DO characterize cases involvemore than three sex chromosomesThree Stages of Prenatal DevelopmentMale and female structural development involves 3 distinct processes 1 Development of gonads 2 Development of internal organs 3 Development of external genitalia In most cases all 3 occur congruently to produce a male or female In rare conditions intersex elements of both male and female development occur in the same fetusThe Development of the Gonads thUp until the 6 week of conception the male and female foetuses have identifcal primordial gonads that have the capacity to develop into ovaries or testes At 6 weeks For malesa gene on the short arm of the Y chromosome the sexdetermining region of the y chromosome SRY is expressed in male embryos Testisdetermining factorthe protein encoded by the SRy gene switches on an additional genes that cause the primordial gonads to develop into testes For Femalesembryos which lack the SRY gene alternate genes guide the development of the primordial gonad into ovaries Chromosomally male mice genetically modified to lack the SRY gene develop ovaries whereas female mice with the SRY gene develop testes
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