Physio Chapter 10 Sexual Behaviour
Children begin to prefer sex-typed toys between the ages of 12 and 18 months.
At these same ages, children are unable to match sex-typed toys (vehicles and dolls) with
male or female faces or voices, suggesting that they have not yet been socialized to think of
toys as male or female
Aristotle argued that the sex of a child was the result of the temperature of semen at the time of
Hot semen resulted in males, and cool semen resulted in females.
Turner's syndrome: child receives only a single X chromosome (XO)
1 2500 live births
Asingle X chromosome carries sufficient genetic material to produce an individual who is
quite normal in many ways.
However, the lack of a second sex chromosome does have an impact on fertility, growth,
and hormone production and is associated with higher risk of diabetes, osteoporosis, and
normal female external genitalia, but the ovaries develop abnormally
the ovaries do not produce either ova or normal levels of female hormones, leading to
inability to produce normal hormone levels (eggs) = infertility
Intelligence is normal, but specific deficits in spatial relationships and memory can occur
Klinefelter Syndrome: features an XXY genotype.
Individuals are male, but they usually experience reduced fertility and require hormone
treatment at puberty to promote the development of secondary male sex characteristics
(facial hair, deeper voice, development of external genitalia) and to inhibit female
characteristics such as breast development
is one of the most common genetic abnormalities related to the sex chromosomes, occurring
in 1.79 out of 1,000 male births
normal intelligence, but mild cognitive difficulties (delayed and reduced verbal skills) and
1 out of 1,000 male births
The physical and behavioral correlates of the condition are typically subtle and generally do
not prompt the parents to seek a postnatal genetic analysis
The boys appear to be physically within typical limits, although they tend to be somewhat
taller and leaner, suffer from acne, and have a higher risk for minor physical abnormalities
of the eye, elbow, and chest
Average IQ scores are slightly below the average of males with normal XY genotypes
Men with the XYY genotype are fertile, but they are slightly more likely than typical men to
produce sperm with sex chromosome abnormalities
The popular press immediately embraced the hypothesis that an extra Y chromosome would
produce a violent super male. - This was false the majority of the criminal behavior of the XYY men involved property crimes rather
than violent crimes.
In comparison to genetic abnormalities like Down syndrome, abnormalities due to a third sex
chromosome appear to have relatively mild effects
a study of more than 13,000 newborns over a 13-year period, found that none of the children
with three sex chromosomes were mentally retarded and that all were in regular public
no increases in criminal activity, mental disorders, or physical disorders relative to the
population with typical sex chromosomes
Three Stages of Prenatal Development
Male and female structural development involves three distinct processes: the development of
gonads, of internal organs, and of external genitalia.
In the majority of cases, all three processes occur congruently to produce an unambiguous
male or female.
In a rare condition known as intersex, elements of both male and female development
occur in the same fetus.
The Development of Gonads
both male and female fetuses have identical primordial gonads that have the capacity to
develop into either ovaries, the female gonads, or testes, the male gonads.
At about six weeks after conception, a gene on the short arm of the Y chromosome,
known as the sex-determining region of the Y chromosome, or SRY, is
expressed in male embryos
Testis- determining factor, the protein encoded by the SRY gene, switches on
additional genes that cause the gonads to develop into testes.
In female embryos, which lack the SRY gene and its ability to produce testis-determining factor,
alternate genes guide the development of the primordial gonad into ovaries
Male mice genetically modified to lack the SRY gene develop ovaries, whereas female mice in
which the SRY gene has been inserted develop testes
Differentiation of the Internal Organs
The differentiation of the internal organs, follows the development of the gonads
Until about the third month of development in humans, both male and female fetuses possess a
male Wolffian system and a female Mllerian system.
In males, the Wolffian system will develop into the seminal vesicles, the vas deferens, and
In females, the Mllerian system will develop into the uterus, the upper portion of the
vagina, and the fallopian tubes
During the third month, the males relatively new testes begin to secrete two hormones,
testosterone and anti-Mllerian hormone
Testosterone, one of several types of male hormone or androgen, promotes the
development of the Wolffian system.
Anti-Mllerian hormone initiates the degeneration of the Mllerian system.
In the female fetus, no additional hormones are needed for development. Unlike the testes, the
ovaries are not active during fetal development. In the absence of any androgens or anti-Mllerian hormone, the Mllerian system will
develop in the typical female direction. Nonfunctional remnants of the Wolffian system
remain throughout a womans life.
Androgen insensitivity syndrome (AIS) disrupts the normal development of the Wolffian
system in males
a defective gene produces abnormal androgen receptors .As a result, the fetuss tissues are
blind to the presence of androgens.
Fetuses with AIS have an XY genotype and normal testes. The testes release androgens and
anti-Mllerian hormone in a normal manner, but the lack of functional androgen receptors
prevents the development of the Wolffian system.
However, anti-Mllerian hormone still works normally, so the female Mllerian system also
fails to develop.
Because the Mllerian system is responsible for the upper two thirds of the vagina, the
result is a shallow vagina and no ovaries, fallopian tubes, or uterus.
Although adult individuals withAIS are infertile, their external appearance is quite
Individuals with AIS are genetic males but typically have female appearance and strong
female gender identities
Development of the External Genitalia
The development of the external genitalia follows the differentiation of the gonads during the
sixth week after conception. The male external genitalia include the penis and scrotum. The
female external genitalia include the labia, clitoris, and outer part of the vagina.
No hormonal activity is required in order to develop female external genitalia. However,
hormonal stimulation is essential for the development of male external genitalia