Chapter 2- RP
Biologically and Physiologically Defining Sex
Definitions of Sex: Scientists define sex in three specific ways:
Biological Sex: Refers to the physical and physiological differences.
Genetic Sex: Based on the sex chromosomes present in an organism.
Gonadal Sex: Refers to the type of gonads (ovaries or testes) present.
Phenotypic Sex: Relates to the external physical characteristics (such as genitalia).
Clarifications:
It's important to note that:
Sex is NOT the same as gender (discussed in Chapter 4).
Sex is NOT the same as gender identity (discussed in Chapter 4).
Sex is NOT the same as sexual orientation (discussed in Chapter 4).
Part 1: Determination of Sex
Genetic Sex (p. 36-37)
Definition: Genetic sex refers to the complement of sex chromosomes present in cells.
Somatic Cells: Human somatic cells contain a total of 46 chromosomes.
Gametes: Human gametes contain 23 chromosomes:
Eggs contain one X chromosome.
Sperm cells can contain either an X or a Y chromosome.
Fertilization Process: The nuclei of gametes fuse during fertilization, resulting in a zygote with 46 chromosomes.
Genetic Sex Outcome: The genetic sex at conception can either be XX (female) or XY (male).
Note: There is no inherent 'default' sexual outcome from a genetic perspective.
Gonadal Sex (p. 37-42, omitting boxes 2.2 and 2.3)
Definition: Gonadal sex refers to the presence of ovaries or testes in an organism.
Indifferent Gonadal Development: Gonadal tissue remains indifferent for about 5 weeks after conception,
Bipotential Gonad: The structure can develop into either an ovary or a testis.
Mullerian Ducts: These can mature into the fallopian tube, uterus, or cervix.
Wolffian Ducts: These can develop into the epididymis, seminal vesicle, and vas deferens.
Influence of Y Chromosome:
The presence of a Y chromosome leads to the formation of testes.
Functional Testes Functions:
Produce testosterone, which promotes the development of the Wolffian ducts.
Trigger programmed cell death of the Mullerian ducts, converting them to a male system.
Development Actions with Y Chromosome:
The Y chromosome contains the Sex-Determining Region of Y (SRY) gene.
Role of SRY Gene:
Transcription and translation result in the SRY protein, which is a transcription factor.
This factor influences other genes that lead to the formation of testicles while silencing ovarian genes.
Functional testes contain Leydig cells (which produce testosterone) and Sertoli cells (which produce anti-Mullerian hormone, AMH).
Testes Functions Recap:
Leydig Cells: Responsible for testosterone production, stimulating Wolffian duct development.
Sertoli Cells: Produce AMH, destroying Mullerian duct structures.
End Result: Gonads develop into testes, and the Wolffian ducts become structures such as the epididymis and seminal vesicles.
Recap on Gonadal Sex (XY Genotype)
Development Phases:
Undifferentiated System: Initial stages involve SRY gene activation leading to the formation of male differentiations.
Testicular Development:
Testis-determining factor (TDF) is produced, leading to the development of testes and male reproductive structures.
Hormonal Release: Testosterone (and Müllerian inhibiting substance) promotes further male reproductive structure development.
Absence of Y Chromosome (Genetic Sex XX)
Absence Consequences:
No Y chromosome means no SRY gene.
Without SRY, there are no testicles or SOX-9 expression.
Lack of testosterone prevents the modification of sexual development, allowing the bipotential gonads to develop into ovaries.
Ovaries initially do not produce significant amounts of estrogen, resulting in the unrestricted development of Mullerian ducts.
Phenotypic Sex (p. 42-43, omit box 2.4)
Definition: Phenotypic sex refers to the visible external genitalia produced, such as a penis or vulva.
Development Timeline: This development occurs typically after gonadal sex has been established (around 8-9 weeks post-conception).
Indifferent Genitalia Stage:
Both female and male genital structures are initially similar, involving:
Genital Tubercle: Can develop into either the clitoris or glans penis.
Genital Folds: Can create the shaft of the penis or labia minora.
Genital Swelling: May develop into either the scrotum or labia majora.
Hormonal Influence:
The presence of androgens, specifically testosterone, masculinizes external genitalia during development.
Testosterone Conversion: Testosterone is converted into dihydrotestosterone (DHT) through the enzyme 5-alpha reductase.
DHT Characteristics: Even though DHT is produced in lesser quantities, it is more potent and critical for male external genitalia formation.
Collectively, testosterone and its analogs are termed androgens.
Absence of Androgens:
In females, without testosterone (and thus without DHT), the developing external genitalia will feminize.
Part 2: Disorders of Sexual Development
Conditions That Challenge Binary Understanding (p. 42-43)
Disorders of sexual development can arise from:
Chromosomal abnormalities,
Hormonal issues or enzyme deficiencies,
Deviations from typical developmental plans.
Examples of Disorders of Sexual Development
Agonadism
Definition: Refers to the absence of gonads, which is very rare.
Both Mullerian and Wolffian ducts may still be present.
Often linked to chromatin structural problems on the X chromosome and can lead to severe cognitive impairments.
Congenital Adrenal Hyperplasia (CAH)
Description: A condition where adrenal glands overproduce androgens affecting both sexes.
Frequency: Occurs in approximately 1 in every 10,000 to 18,000 births.
Masculinization Effects: The excessive androgens can masculinize genitalia, resulting in varying degrees of genital formation.
Role in Sodium Balance: Also affects sodium levels in the body.
Intersex Conditions
Definition: This term describes situations where gonadal sex and phenotypic sex do not align (e.g., a person with testes having feminized external genitalia).
Androgen Insensitivity Syndrome (AIS)
Affected Population: Genetic and gonadal males who have partial or complete insensitivity to androgens (testosterone, DHT).
Prevalence: Occurs in about 1 in 20,000 births.
Observable Effects: Body cannot respond to androgens, leading to the development of female genitalia without menstrual periods and infertility. Testes commonly reside in the abdominal cavity requiring surgical intervention.
Hormone/Enzyme Deficiencies Impacting Differentiation
Variability: Conditions may vary from partial testosterone production to total absence.
As illustrated in case studies of individuals displaying feminized appearance at birth (due to lack of DHT), but can experience genital masculinization at puberty due to testosterone effects.
Nondisjunction Events and Their Consequences
Definition: Nondisjunction refers to chromosomes not separating correctly during meiosis.
This can lead to conditions like trisomy (e.g., Down Syndrome) when involving autosomes.
When involving sex chromosomes, it results in gametes that may have extra or missing sex chromosomes.
Examples of Nondisjunction Results
Potential Gamete Patterns:
Typical Sperm: XY, XX
Typical Egg: XX, XY
Potential Zygote Combinations include XXX, XXY, XYY, etc.
Klinefelter Syndrome (XXY Genotype)
Description: Encountered in 1 in 1,000 to 2,000 births, males with an XXY genotype.
Characteristics include:
Taller stature, small testicular size, often subfertile or infertile,
Gynecomastia (breast tissue development) and atypical body hair growth patterns.
Men often show mild cognitive impairment.
Turner’s Syndrome (XO Genotype)
Description: Found in 1 in 2,000 to 3,000 live births; individuals designated as female due to the absence of one X chromosome.
Symptoms may include:
A webbed neck due to extra skin folds, short stature, widely spaced nipples,
Infantile genitalia, and usually infertile.
Increased risks of cardiovascular complications (narrowing of the aorta).
“Superfemale” Condition (XXX Genotype)
Description: Occurs in about 1 in 1,000 births, usually designated as female and often undiagnosed due to lack of notable symptoms until later stages.
Characteristics might include:
Taller than average stature and potential developmental/intellectual disabilities, with some fertility issues present such as premature ovarian failure.
“Supermale” Condition (XYY Genotype)
Description: Seen in approximately 1 in every 1,000 births; identified as male due to Y chromosome presence.
Characteristics generally observed include:
Heightincreased growth velocity, normal testosterone levels, and standard sexual development and fertility.
Some individuals may exhibit mild intellectual disabilities when evaluated.