Basic Lecture Outline and Notes

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

c.  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.

D.  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.

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.  Intersexuality in a variety of forms occurs in about one of every 2,000 births. There are actually more than 25 intersexual diagnoses.

3.  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.