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Chapter 9Reproductive Behavior

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Sexual DevelopmentProduction of Gametes and Fertilization

Sexually dimorphic behavior:• A behavior that has different forms or that occurs

with different probabilities or under different circumstances in males and females.

Gamete:• A mature reproductive cell; a sperm or ovum.

Sex chromosome:• The X and Y chromosomes, which determine an

organism’s gender. Normally, females are XX and males are XY.


Sexual DevelopmentDevelopment of the Sex Organs

Gonad:• An ovary or testis.

Organizational effect:• The effect of a hormone on tissue differentiation

and development.

Activational effect:• The effect of a hormone that occurs in the fully

developed organism; may depend on the organism’s prior exposure to the organizational effects of hormones.


Sexual DevelopmentInternal Sex Organs

Müllerian system:• The embryonic precursors of the female internal

sex organs.

Wolffian system:• The embryonic precursors of the male internal

sex organs.



Anti-Müllerian hormone:• A peptide secreted by the fetal testes that inhibits

the development of the Müllerian system, which would otherwise become the female internal sex organs.

Defeminizing effect:• An effect of a hormone present early in

development that reduces or prevents the later development of anatomical or behavioral characteristics typical of females.



Androgen:• A male sex steroid hormone. Testosterone is the

principal mammalian androgen.

Testosterone:• The principal androgen found in males.



Masculinizing effect:• An effect of a hormone present early in

development that promotes the later development of anatomical or behavioral characteristics typical of males.

Dihydrotestosterone:• An androgen, produced from testosterone

through the action of the enzyme 5α reductase.


Sexual DevelopmentInternal sex Organs

Androgen insensitivity syndrome:• A condition caused by a congenital lack of

functioning androgen receptors; in a person with XY sex chromosomes, causes development of a female with testes but no internal sex organs.


Sexual DevelopmentInternal sex Organs

Persistent Müllerian duct syndrome:• A condition caused by a congenital lack of anti-

Müllerian hormone or receptors for this hormone; an a male, causes development of both male and female internal sex organs.

Turner’s syndrome:• The presence of only one sex chromosome (an X

chromosome); characterized by lack of ovaries but otherwise normal female sex organs and genitalia.


Sexual DevelopmentSexual Maturation

Gonadotropin releasing hormone:• A hypothalamic hormone that stimulates the

anterior pituitary gland to secrete gonadotropichormone.

Gonadotropic hormone:• A hormone of the anterior pituitary gland that has

a stimulating effect on cells of the gonads.


Neural Control of Sexual BehaviorBrain Mechanisms

Spinal nucleus of the bulbocavernosus:• A nucleus located in the lower spinal cord; in

some species of rodents, present only in males.

Medial preoptic area (MPA):• An area of cell bodies just rostral to the

hypothalamus; plays an essential role in male sexual behavior.



Sexually dimorphic nucleus (SDN):• A nucleus in the preoptic area that is much larger

in males than in females; first observed in rats; plays a role in male sexual behavior.

Periaqueductal gray matter (PAG):• The region of the midbrain that surrounds the

cerebral aqueduct; plays an essential role in various species-typical behaviors, including female sexual behavior.



Nucleus paragigantocellularis (PGi):• A nucleus of the medulla that receives input from

the medial preoptic area and contains neurons whose axons form synapses with motor neurons in the spinal cord that participate in sexual reflexes in males.

Ventromedial nucleus of the hypothalamus (VMH):• A large nucleus of the hypothalamus located

near the walls of the third ventricle; plays an essential role in female sexual behavior.

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