Human Sexual Gender Differentiation All mammals including humans

Human Sexual (& Gender? ) Differentiation

All mammals including humans begin life as embryos that have the potential to be either male or female in three ways Brain External Genitalia Gonads and Internal Duct Systems

Gonads and Internal Duct Systems

Male Differentiation Testes and Ducts SRY Gene H-Y antigen Testes A male has one X and one Y chromosome. The Y chromosome has an SRY gene, that produces a substance called H-Y antigen causes the undifferentiated gonads to become testes.

Female Differentiation Ovaries and Ducts No Antigens produced A female has two X chromosomes. There is no SRY gene, because that gene only exists on a Y chromosome. In the absence of the SRY gene, no H-Y antigen is produced. In the absence of H-Y antigen, the undifferentiated gonads become ovaries.

Development of External Genitalia

Male Differentiation External Genitalia The testes produce testosterone. The testosterone circulates in the bloodstream and is converted to dihydrotestosterone by a substance called 5 alpha reductase. Dihydrotestosterone causes the undifferentiated external genital tissue to develop into the penis and scrotum.

Adult Male External Genitalia

Male Adult Gonads and Ducts

Female Differentiation External Genitalia The Ovaries produce no testosterone. In the absence of testosterone, the undifferentiated external genital tissue develops into the clitoris, labia minora and labia majora.

Adult Female Anatomy

Adult Female Gonads and Ducts

Male Differentiation Brain and Behavior 1. The testes produce testosterone. 2. Testosterone crosses the blood brain barrier into the brain. A substance present in the brain called aromatase converts the testosterone to estradiol, a type of estrogen. Blood-Brain Barrier 3. 4. The Presence of estradiol in the brain causes it to become masculinized. Aromatase Estradiol Testosterone

Female Differentiation Brain and Behavior 2. Estradiol from the Mother crosses the Placenta into the baby’s blood stream 1. There are no testes to produce testosterone that can be converted to estradiol in the brain 3. Alphafetoproteins present in the baby’s system cannot cross the blood-brain barrier. They bind with the estradiol and prevent it from crossing into the brain. 4. The absence of estradiol in the brain causes it to become feminized. Blood-Brain Barrier Estradiol Alpha-fetoproteins

Four Examples of Ways Sexual Differentition Can Go Wrong 1. A genetically male embryo lacks the ability to sense the presence of testosterone. 2. The mother of a genetically male embryo is producing large amounts of adrenaline, which floods the embryo’s body. The adrenaline binds to the receptors that usually detect testosterone, preventing it from being recognized by the body, even if it is present in large amounts. 3. Lack of 5 alpha reductase that converts testosterone to dihydrotestosterone. 4. A genetically female embryo is exposed to external sources of testosterone, or substances that are mistaken for testosterone in the body. Eg. Diethylstilbestrol

Sexual Differentiation Key Terms üX & Y Chromosomes ü 5 alpha reductase üTestis üDNA üDihydrotestosterone üSeminal vesicle üSRY gene üAromatase üProstate üH-Y antigen üAlpha-fetoprotein üVas deferens üGonad üEstradiol üEpididymis üMesonephros üOvary üPenis üMullerian ducts üFallopian tubes üClitoris üWolffian ducts üUterus üScrotum üTestosterone üVagina üVulva (Labia)

Ambiguous Genitalia

Hermaphrodite Genitalia

Surgical Reconstruction to Female

Surgical Reconstruction to Male