Sexual Development
 Aristotle argued that
hot semen = boys, cold semen = girls
 Mother’s provide an X chromosome to all offspring.
Father’s chromosome (X or Y) will determine the sex of
the baby
 A fetus not exposed to male hormones would have the
physical appearance and behavior of a girl
Wolffian system - The internal system that develops into
seminal vesicles, vas deferens, and the prostate gland in
males.
Müllerian system - The internal system that develops into a
uterus, fallopian tubes, and the upper two thirds of the
vagina in the absence of anti-Müllerian hormone
Anti-Müllerian Hormone - A hormone secreted by fetal
testes that causes the degeneration of the Müllerian system.
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The testes during this time secretes male hormones
“testosterone” & “anti-Mullerian Hormone” promotes
the development of the Wolffian System
Sex Chromosome Abnormalities
Androgen - a steroid hormone that develops and maintains
typically masculine characteristics.
Turner Syndrome
 child receives only a single X chromosome and no X or Y.
example: (XO)
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higher risk of diabetes, osteoporosis, and
cardiovascular disease
 Has a normal female genitalia; abnormal ovaries that
doesn’t produce ova or normal level of female
hormones leading to infertility
 Relatively short
Androgen insensitivity syndrome (AIS)
 disrupts the normal development of the Wolffian
system in males.
 genetic male fetus lacks androgen receptors, which
leads to the development of female external genitalia
and typically female gender identity and sexual behavior.
 People with AIS despite being genetically males identify
and appear as females.
Gender Identity - The sense of being male or female,
independent of genetic sex or physical appearance.
Klinefelter Syndrome
 A condition in males caused by an XXY genotype
 characterized by frequent problems with fertility,
secondary sex characteristics (facial hair, deep voice),
and delayed verbal skills.
 Commonly left handed
 Taller, leaner, suffer from acne
Note: XYY genotype; extra Y chromosome tend to produce a
violent “super male”
3. Development of the External Genitalia
 Development of either 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 if required for the development of
female genitalia
 Androgen called 5-alpha-dihydrotestosterone secreted
by the testes that develops the external male genitalia.
Down Syndrome
 3 copies of chromosome 21; Trisomy 21
 no increases in criminal activity, mental disorders, or
physical disorders
Three Stages of Prenatal Development
1. Development of Gonads
 Have the potential to create ovaries or testes up until
the 6th week of conception
Sex-Determining Region Of The Y Chromosome (SRY) - A
gene located on the short arm of the Y chromosome that
encodes for testis-determining factor.
Congenital Adrenal Hyperplasia (CAH)
 Is when a genetic female is prenatally exposed to
androgen resulting to masculinization of external
genitalia
 Males can be affected by CAH too but it is more
apparent in females
 clitoris is enlarged, the labia look similar to a scrotum,
and in some cases, there is no vaginal opening.
 Some are Tomboys, engage in bisexual and lesbian
behavior. Majority are heterosexual
Development at Puberty
Testis-Determining Factor - A protein encoded by the SRY
gene on the Y chromosome that causes the primordial
gonads to turn into testes
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Note: lack of SRY chromosome will lead to the development
of ovaries in females
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2. Differentiation of the Internal Organs
 3rd month both make and female fetus possess a
wolffian and mullerian system
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Development of secondary sex characteristics I.e.
deeper voice in males and breast development
Dropped from age 16 to 12 due to increased obesity
might signal to puberty
Low body fat such as in anorexia nervosa might delay
puberty
Exposure to compounds similar to female hormones
trigger earlier puberty
All edible tissues from animals contain a type of
estrogen, or female hormone, called estradiol
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Phthalates, compounds frequently found in plastics and
cosmetics, have been found to advance puberty
Onset of puberty is due to the release of GnRH
GnRH initiates the release of 2 gonadotropic hormone
follicle-stimulating hormone (FSH) and luteinizing
hormone (LH)
In response to stimulation by FSH and LH, the testes
begin to produce additional testosterone, and the
ovaries produce estradiol
Testes also produce small amounts of estrogens,
including estradiol, and the ovaries produce small
amounts of androgens, including testosterone.
Males
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burst of additional androgens stimulates muscular
development, maturity of genitalia, deeper voice.
LH, FSH, and Testosterone regulate sperm production,
and affect hairline
Females
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In females, estradiol produces breast growth, maturity
of the external genitalia, maturity of the uterus, and
changes in fat distribution and quantity
5 alpha-reductase deficiency
 A rare condition in which a child is born with ambiguous
genitalia but develops male secondary sex
characteristics at puberty.
Hormones and Sexual Behavior
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sex hormones activate and organize circuits in the brain
that differ according to sex.
Both male and female produce androgen and estrogen
Regulation of Sex Hormones by the
Hypothalamus and Pituitary Gland
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Light inhibits melatonin therefore increasing secretion
of GnRH
 Amount of daylight hours provide means for producing
offspring.
 Fertility is high during the summer
Males - LH signals for sperm production; Testosterone and
FSH is responsible for sperm maturation.
Females - FSH and LH control the menstrual cycle
Menstrual Cycle and Female Fertility
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1st day of menstruation signals secretion of FSH and
develops follicles in the ovaries containing an ovum.
Follicle - several clusters of cells in the ovary each of which
contains an egg cell. ovum A female reproductive cell, or egg
 The single rapid growing follicle release estrogen to
inhibit the growth of others.
 Glands release LH inititiating the release of the ovum
leading to ovulation
 Estradiole signals the uterus to thicken after 2 weeks
from the 1st day of menstruation
 Corpus luteum (ruptured follicle) release estradiole and
progesterone to develop the lining in the uterus
 When progesterone level drops the lining cannot be
maintained and sheds
Premenstrual Syndrome - A condition in which some
women experience physical and psychological symptoms
immediately prior to the onset of menstruation.
Premenstural Dysphoric - disorder (PMDD) A condition
in which premenstrual mood changes are unusually severe.
Postpartum Depression - A condition in which mothers
who have recently given birth experience feelings of
depression due to their rapidly changing hormonal
environment.
Note: Higher risk for postpartum is young, less educated, low
socioeconomic status
Female Contraception
1. Breast feeding - suppresses GnRH
2. Oral contraceptives - interfere with normal ovulation.
- combination (estrogen and
progestin) prevents the maturation
of follicles and ovulation
- progestin only prevents the prevents
the thinning of cervical mucus that
typically accompanies ovulation.
3. Norplant method - tubes that release a progestin over a
period of six months is implanted on the woman’s upper arm
4. Medroxyprogesterone acetate(MPA) - similar in chemical
structure to progesterone and acts to suppress ovulation,
administered via injection every 3 months
5. “morning after” pill - series of typical birth control pills
taken at specified time intervals to interfere with
implantation of the embryo
6. Copper-bearing intrauterine wires (IUD)
7. Mifepristone/RU-486 - the abortion pill interrupts
pregnancies up to 9 weeks from conception by blocking the
action of progesterone
Sex Hormones and Female Behavior
Estrus - a period of hours or days in which the female is
receptive to males, hormones play an important role in
determining the timing and frequency of sexual behavior.
Sexual Interest in Human Females
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A woman’s sexual drive is influenced by testosterone
levels. Also produced in small amounts by the ovaries
Estrogens and Cognition
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High perfomance scores when testosterone is high; low
when estrogen
Estrogen replacement therapy (ERT), particularly in the
few years immediately following menopause, is helpful
in preventing later cognitive decline.
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Sex Differences in the Nervous System
Sexually Dimorphic - Displaying structural differences
between the sexes.
 Bigger SDN-POA in male rats (only in rats)
 Interstitial nuclei of the anterior hypothalamus, or INAH.
INAH-2 and INAH-3 are about twice as large in males as
in females (humans)
 Male rats have more motor neurons in a structure
known as the spinal nucleus of the bulbocavernosus
(SNB) than do female rats.
Aromatization - A chemical reaction resulting in an aromatic
compound. Testosterone is transformed into Estradiol
Alpha Fetoprotein - A substance circulated by rats that
deactivates estradiol and prevents maternal estradiol from
masculinizing female pups.
Sexual Orientation
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Sex Hormones and Male Behavior
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Androgens influence male competitiveness, sexual
frequency, and cognition.
Androgens and Competition
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Steroids also produce significant side effects such as
acne, enlargement of the clitoris or penis, a lower voice,
unusual hair loss or growth, high blood pressure, and
kidney disease
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testosterone levels appear to increase in anticipation of
a competition.
Has a correlation to sports
abnormal conditions such as CAH, which involves
prenatal exposure to androgens, can increase the
likelihood that women will engage in bisexual or lesbian
behavior as adults. However, the majority of CAH
women are heterosexual. Also, the majority of lesbian
and bisexual women do not have a history of CAH or
similar conditions
exposure to prenatal androgens may have influenced
both the ear structure and sexual orientation of the
lesbian and bisexual women.
Brain Structure
Androgens and Sexual Interest
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Used on sexual offenders MPA reduces circulating
testosterone levels in men to pre-puberty levels,
generally eliminating any sexual activity
Men in long term relationships have lower T because of
the reduced competition
Men with lower T have shown to be more successful in
maintaining marriages
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INAH-3 was two to three times larger in heterosexual
men than in homosexual men
chances of a homosexual male twin having a
homosexual brother are 20 to 25 percent for fraternal
twins and about 50 percent for identical twins.
Compared with mothers with heterosexual sons,
mothers of homosexual sons showed more extreme
skewing, in which one X chromosome is much more
likely to be inactivated than the other
Androgens and Cognitive Behavior
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Men are commonly believed to have slight advantages
over women in tasks involving spatial relations due
testosterone
Male Contraceptives
1. Condoms
2. Withdrawal
3. Vasectomies
4. “Intra Vas” - device that physically blocks the movement
of sperm
Anabolic Steroids
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synthetic versions of testosterone that build tissue,
have legitimate medical uses in cases of malnutrition
and other tissue loss
Attraction
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Highly symmetrical bodies are generally healthier, and
some researchers believe that we are programmed to
select healthy mates
More symetrical men are more likely to cheat on their
partners
Men pay more attention to women’s figures than
women pay to men’s physiques because it represents
reproductive fitness
Major histocompatibility complex (MHC) - genes code for
our immune system’s ability to recognize intruders. It is to
your advantage to find a mate whose MHC profile is as
different as possible from your own because this will result in
the best immune system possible for your children.
- Might account for female human preferences for male
odors
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oxytocinand vasopressin are involved in romantic love
and parenting bonding
vasopressin is expressed more by males and oxytocin by
females
overriding goal of sexual behavior is the production of
offspring who will survive to reproduce
Monogamy would help the mother retain the protection
and other benefits offered by a father. Unfortunately,
these characteristics do not always coexist in the same
man.
Monogamy - The custom of having one mate at a time or for
life.
Erectile Dysfunction - The inability to get and maintain
an erection long enough for satisfactory sexual activity.