Download II. Development of Sex Organs

Chapter 9
Reproductive Behavior
Basic Lecture Outline and Notes
Sexual Development
I.
Production of Gametes and Fertilization
A. Haploid Cell – gametes- single set of chromosomes specialized for sexual
reproduction.
a. Ovum
b. Sperm
B. Diploid Cell - What are produced when a single sperm cell fuses with an
ovum.
C.
Sex Chromosomes
a. Twenty-two pair of autosomes
b. Twenty-third pair determines genetic sex.
a. Ovum = X
b. Sperm = X or Y
 on Y chromosome is the SRY gene. This gene contains the
testis determining factor (TDF).
II.
Development of Sex Organs
A.
7th week – 12th week – Until the 7th week we are identical.
B.
Nature’s impulse is to create a female.
1.
Now gender will be determined through organization and
activation.
a.
Gonads – Testes or Ovaries
 Y Chromosome SRY gene – testes determining factor
 SRY gene makes undifferentiated gonads into testes – if
gene is inserted in XX the animal will be MALE.
C.
3rd month – Internal sex organs
1.
Mullerian System – (precursor of female) fimbriae, Fallopian
tubes, the uterus and the inner two-thirds of the vagina.
2.
Wolffian system – (precursor of male) epididymis, vas deferens,
seminal vesicles, prostate
a.
Testes secrete anti-mullerian hormone and androgens –
(testosterone and dyhydrotestosterone)
b.
Persistent Mullerian Duct Syndrome – defective
receptors for mullerian-inhibiting hormone. (this mullerian
inhibiting hormone has a defeminizing effect) but with no
receptors Genetic male XY but person has both sets of
internal organs because nature’s impulse is to create a
female
Androgen insensitivity syndrome – means there are no
androgen receptors – result is genotypic male that is
phenotypically female.
d.
No internal organs female because the mullerian-inhibiting
substance prevents the female internal sex organs from
developing, but there are external female genitalia because
natures’ impulse is to create female. And without the
androgen receptors, even though the hormone is there, there
is no receptor for it so a phenotypic female results with
shallow vagina, no uterus or ovaries.
e.
Turner’s Syndrome – XO defective sperm. Need XX to
produce ovaries. No ovaries but normal female internal sex
organs and external genitalia. Sterile – because they have
no ova.
External Genitalia
1.
Visible Sex organs – The gender of a person’s external genitalia is
determined by the presence or absence of testes and the hormones
they produce.
a. CAH – Congenital Adrenal Hyperplasia –Adrenal glands in
46 XX females adrenal cortex secretes abnormally high amounts of
androgens – This accounts for almost ½ of group to intersexuals
with ambiguous external genitalia. This is caused by recessive
mutant genes.
 In 46 XX genetic females the result is extreme genital and
behavioral masculinization.
c.
D.
b. 5-Alpha Reductase Deficiency 5- alpha reductase is a
steroid that is responsible for converting testosterone produced by
the Testis in to the biologically active steroid dihydrotestosterone
in target cells.
During gestation, the development of the internal sexual ducts
in males – the Wolffian system – is controlled by testosterone
and therefore is normal.
During this same period, the differentiation of the external
male genitalia – the scrotum and the penis –is regulated by
dihydrotestosterone, and they therefore fail to develop.
As a result, the external appearance of the newborn male is that
of a female baby. Such children are raised as females and
consider themselves to be girls. They look forward to
acquiring female sexual characteristics at puberty.
At puberty, unexpected developments take place. These little
girls rapidly increase their muscle mass, grow larger bones, and
gain deeper voices. An almost normal sized male penis and
mature scrotum appear. It appears that testosterone – not
dihydrotestosterone- governs the secondary sexual
characteristics at puberty.
2.
3.
Intersexuality in a variety of forms occurs in about one of every
2,000 births. There are actually more than 25 intersexual
diagnoses.
Nearly all intersexual babies are assigned to be female, because the
surgical techniques are better. Since 1950 the protocol in the U.S.
has been for doctors to assign sex, operate and shield the family for
the notion that their baby’s gender is in question.
Hormonal Control of Sexual Behavior
A.
Organizational Effects of Prenatal Androgens.
1.
A myth should be dispelled immediately is that men and women
would exchange their behavioral roles if their hormonal balances
were reversed.
2.
Prenatal androgenization does effect development of the human
brain. These androgens may have defeminizing and masculinizing
effect on human sexual behavior just as they do in other mammals.
 If rodent’s brain is not exposed to androgens during a critical
period of development, the animal will engage in female sexual
behavior as an adult.
 If it is exposed to androgens during development behavioral
defeminization and behavioral masculinization will occur.
 It appears we are sexually dimorphic – difference between
male and female is the differential exposure to androgens
prenatally and during early postnatal life.
 30 young women with CAH described their sexual orientation
– 37% bisexual or homosexual. 40% exclusively heterosexual
and 23% declined to respond. If the noncommittal women are
excluded from the sample the percentage of homo or
bisexuality rises to 48%.
 It appears that from the Kinsey report where 10% of American
women reported some sexual contact with another woman by
the age of 20 – the sample of androgenized women was 4 times
as high.
Neural Control of Sexual Behavior
A. Changes in Brain structure –
 Suprachiasmatic nucleus of hypothalamus is larger in
homosexual men and smaller in heterosexual men and women.
 Sexually dimorphic nucleus is larger in heterosexual men and
smaller in homosexual men and heterosexual women
 Anterior Commisure is larger in homosexual men and
heterosexual women and smaller in heterosexual men.
 The brains of heterosexual women, heterosexual men and
homosexual men may have been exposed prenatally to
different patterns of hormones.
 Prenatal Stress suppressed androgen production – caused
the sexually dimorphic nucleus to be smaller which is normally
larger in males than females. thus interfering with the
defeminization of the sexual behavior of a male offspring. – –
the same nucleus that is found to be smaller in homosexual
men.
 Another factor is heredity – studies of identical twins 52% as
opposed to 22% for fraternal twins.