lec 5

Questions and Answers

What is the default sex of mammalian embryos?

Female (correct)

Male

Hermaphrodite

Undifferentiated

Which gene is responsible for determining testicular differentiation in mammals?

SRY (correct)

Sox9

TDF

Wnt4

What is the name of the ridge of tissue on the surface of each mesonephros where gonadal differentiation begins?

Germinal ridge (correct)

Nephronic ridge

Primordial ridge

Meso ridge

What is the function of Sertoli cells in testicular differentiation?

To direct the remainder of testicular differentiation Signup and view all the answers

What is the name of the gene that codes for the SOX9 transcription factor?

Sox9 Signup and view all the answers

At which stage of development is the gonadal sex determined?

Gonadal sex Signup and view all the answers

What is the location of the SRY gene in the Y chromosome?

On the tip of the Y chromosome Signup and view all the answers

What is the term for the bipotential tissue that can develop into either a testis or an ovary?

Bipotential tissue Signup and view all the answers

What is the primary focus of today's lecture?

Sex determination and sexual differentiation Signup and view all the answers

What determines whether an individual will become male or female?

Sex determination Signup and view all the answers

What is the developmental process of becoming male or female?

Sexual differentiation Signup and view all the answers

What are the levels of sex that contribute to an organism's sexual phenotype?

Chromosomal sex, gonadal sex, and gametic sex Signup and view all the answers

What is the purpose of the lecture on sex determination and sexual differentiation?

To describe the process of sex determination in mammals Signup and view all the answers

What are the three aspects of sexual differentiation that will be covered in the lecture?

Differentiation of the gonads, internal reproductive tract, and external genitalia Signup and view all the answers

What are the consequences of disorders in sex determination and sexual differentiation?

All of the above Signup and view all the answers

What is the significance of understanding sex determination and sexual differentiation?

It is essential for understanding human development and reproductive biology Signup and view all the answers

What is the primary factor that determines the development of Wolffian ducts into the male internal reproductive tract?

Testosterone Signup and view all the answers

Which of the following ducts develops into the female internal reproductive tract?

Müllerian ducts Signup and view all the answers

What is the role of Mullerian-inhibiting-hormone (MIH) in reproductive tract development?

Inhibits the development of Müllerian ducts Signup and view all the answers

Which of the following structures is NOT a part of the male internal reproductive tract?

Uterus Signup and view all the answers

What is the primary function of the urogenital sinus during early embryonic development?

Connects the gonads to the urinary and reproductive tracts Signup and view all the answers

What happens to the Wolffian ducts in the absence of testosterone?

They regress and disappear Signup and view all the answers

What is the fate of Mullerian ducts if MIH is present?

They regress Signup and view all the answers

What is the role of dihydrotestosterone in the differentiation of external genitalia in males?

It is necessary for the formation of the scrotum Signup and view all the answers

What is the characteristic of True Hermaphroditism?

The presence of both ovarian and testicular tissue Signup and view all the answers

What is the genetic makeup of individuals with Turner Syndrome?

45,XO Signup and view all the answers

What is the usual symptom of Triple X Syndrome?

Taller than average Signup and view all the answers

What is the characteristic of ovaries in individuals with Turner Syndrome?

They are incompletely developed and do not produce steroid hormones Signup and view all the answers

What is the inheritance pattern of Congenital Adrenal Hyperplasia?

Autosomal recessive Signup and view all the answers

What is the role of 5α-reductase in the differentiation of external genitalia?

It converts testosterone to dihydrotestosterone Signup and view all the answers

What is the fate of the genital tubercle in the absence of androgens?

It forms the clitoris Signup and view all the answers

What is the characteristic of the genital folds in the presence of androgens?

They form the scrotum Signup and view all the answers

What is the primary cause of Congenital Adrenal Hyperplasia (CAH) in chromosomal females?

21-hydroxylase enzyme deficiency Signup and view all the answers

What happens to the precursor hormones in the adrenal glands of chromosomal females with Congenital Adrenal Hyperplasia (CAH)?

They are converted into androgens Signup and view all the answers

What is the effect of low cortisol levels on the hypothalamus and anterior pituitary in chromosomal females with Congenital Adrenal Hyperplasia (CAH)?

Decreased negative feedback Signup and view all the answers

What is the effect of high androgens on the external genitalia of chromosomal females with Congenital Adrenal Hyperplasia (CAH)?

Masculinization Signup and view all the answers

What is the characteristic of Complete Androgen Insensitivity Syndrome (AIS)?

Female body type and female gender identity Signup and view all the answers

What is the effect of 5a-Reductase Deficiency on the development of chromosomal males?

Blocking the conversion of T to DHT Signup and view all the answers

What is the difference between Complete Androgen Insensitivity Syndrome (AIS) and Incomplete (Partial) AIS?

Complete AIS has only female characteristics, while Incomplete AIS has both male and female characteristics Signup and view all the answers

What is the treatment for Congenital Adrenal Hyperplasia (CAH) in chromosomal females?

Surgery and exogenous steroids Signup and view all the answers

Study Notes

Overview of Sexual Differentiation

Sex determination is the event that determines whether an individual will become male or female.
Sexual differentiation is the developmental process of becoming male or female.
There are different levels of sex, including chromosomal sex, gonadal sex, hormonal sex, morphological sex, behavioral sex, gender identity, and legal sex.

Jost's Model of Sexual Differentiation

Jost's model describes the process of sexual differentiation, including genetic sex, gonadal sex, and phenotypic sex.
The model shows how genetic sex determines gonadal sex, which in turn determines phenotypic sex.

Differentiation of the Gonads

The germinal ridge is a thickened ridge of tissue on the surface of each mesonephros (protokidney) that can develop into either a testis or an ovary.
The SRY gene on the Y chromosome codes for the SRY transcription factor, which leads to the differentiation of Sertoli cells and the remainder of testicular differentiation.
In the absence of SRY, the embryo develops as female by default.

Differentiation of the Internal Reproductive Tract

Two duct systems are present in each embryo, connecting the gonads to the urogenital sinus.
Wolffian ducts develop into the male internal reproductive tract in the presence of testosterone.
Müllerian ducts develop into the female internal reproductive tract in the absence of Müllerian-inhibiting hormone (MIH).

Differentiation of the External Genitalia

Bipotential precursor tissues in a fetus give rise to the external genitalia.
In males, the genital tubercle develops into the penis, and the genital folds develop into the scrotum, in the presence of androgens.
In females, the genital tubercle develops into the clitoris, and the genital folds develop into the labia, in the absence of androgens.

Disorders of Sexual Differentiation

True hermaphroditism occurs when both ovarian and testicular tissue are present in the same individual.
Turner syndrome (XO) is a condition where one X chromosome is completely or partially missing, resulting in immature genital tracts and external genitals, short stature, and heart defects.
Triple X syndrome (XXX) is a condition where an individual has an extra X chromosome, resulting in taller stature, normal sexual development, and usually not sterile.
Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder where an enzyme deficiency leads to the production of androgens instead of cortisol, resulting in masculinization of the external genitalia.
Androgen insensitivity syndrome (AIS) is an X-linked disorder where defective androgen receptors lead to total or partial androgen insensitivity, resulting in varied phenotypes and gender identity.
5α-reductase deficiency is a condition where the enzyme that converts testosterone to dihydrotestosterone is absent, resulting in varied phenotypes and gender identity.

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Description

This quiz covers the biology of sex determination and sexual differentiation, including an overview of the process and key concepts. Review the lecture notes and announcements before taking the quiz.