Session 1 - Notes

Question 1

Define genotype

Answer 1

The genetic makeup of an individual as defined by the particular sets of genes they possess

Question 2

Define phenotype

Answer 2

The observable physical characteristics of an individual as determined by their genes

Question 3

Should the external genitalia be ambiguous at birth, suggest what investigations may
be undertaken to assign sex.

Answer 3

Information on karyotype, gonadal sex, hormonal tests, and anatomy)

(e.g., palpation of gonads, length and diameter of any phallus, position of urethral meatus,
degree of labio-scrotal fold fusion, presence of vagina/pouch/urogenital sinus) (including
ultrasound study).

Question 4

What tissue forms the matrix of the gonads in which the primordial germ cells migrate?

Answer 4

somatic mesenchymal tissue

Question 5

An individual has a genotype of XXY. Will they have ovaries or testis? Explain your
answer.

Answer 5

Testes

Question 6

Which gene on the short arm of the Y chromosome determines formation of the
testes?

Answer 6

SRY gene (sex determining region of Y gene) also called TDF gene (testis determining 
factor)

Question 7

What will be the presenting sign of Turner’s syndrome (45 XO) at puberty

Answer 7

Failure to menstruate

Failure of secondary sexual characteristics

Question 8

Which hormones prevent the spontaneous development of the female genitalia in the
male and from which cells are they secreted?

Answer 8

Interstitial cells of Leydig in the testes secrete androgens, principally testosterone, from 9
weeks gestation.

Sertoli cells lie within the walls of the seminiferous tubules and secrete MIH (Müllerian
inhibitory hormone; MIS Müllerian inhibitory substance)

Question 9

What structures do the Müllerian ducts develop into?

Answer 9

uterine tubes
uterus
cervix

Question 10

Which structures do the Wolffian ducts develop into?

Answer 10

epididymis
vas deferens
seminal vesicles

Question 11

The prostate develops from the urogenital sinus in the male (under the influence of
testosterone), but what does the urogenital sinus form in the female?

Answer 11

(Lower part of) vagina

Question 12

What would occur in a male (XY) with low levels of MIH or resistance to MIH?

Answer 12

The presence of testicular testosterone will promotes male external genitalia and
Wolffian ducts, but the Müllerian ducts are also retained. Hence, genetically and gonadally
male but with internal genitalia of both sexes

Question 13

What are the mesoneprhic and paramesonephric ducts?

Answer 13

Pair of ducts which end at cloaca and develop in both males and females,

Question 14

Outline the process of mesonephric duct making contact with urogenital sinus in both male and female

Answer 14

• Mesonephric ducts reach Urogenital sinus
• Ureteric bud sprouts from mesonephric duct
• Smooth musculature begins to appear, UGS begins to expand

Question 15

What happens to mesoneprhic duct in male?

Answer 15

• Ureteric bud & MD make independent openings in UGS

* Prostate and prostatic urethra form

Question 16

What happens to mesonephric duct in female?

Answer 16

• Mesonephric ducts regresses due to lack of androgens

* Ureteric bud opens into urogenital sinusW

Question 17

What are the paramesonephric ducts?

Answer 17

Arise close to mesonephric ducts, no relation to kidney function. Actually invaginations of epithelium of urogenital ridge. Fuse to form fallopian tube and uterus.

Question 18

What happens to paramesonephric ducts in males?

Answer 18

• Androgen secretion supports mesonephric ducts

* Testis secretes Mullerian Inhibiting Substance -> Paramesonephric duct degenerates

Question 19

What happens to paramesonephric ducts in females?

Answer 19

• No androgen -> Mesonephric duct degenerates

* No testis derived Mullerian Inhibiting Substance -> Paramesonephric duct degenerates

Question 20

What are the three basic components of genital development in both male and female

Answer 20

• Genital tubercle
• Genital folds
• Genital swellings

Question 21

What happens to 
•	Genital tubercle
•	Genital folds
•	Genital swellings
in MALE

Answer 21

Driven by dihydrotestosterone
Genital tubercle – Elongates to form penis
Genital folds – Fuse to form spongy urethra
Genital swellings -> Fuse to create the scrotum

Question 22

What happens to 
	Genital tubercle
•	Genital folds
•	Genital swellings
in FEMALES

Answer 22

Drive by absence of dihyrdotestosterone
Genital tubercle – Becomes the clitoris
Genital folds – No fusion, become labia minora
Genital swellings – Become labia majora

Question 23

Outline the descent of the testes

Answer 23

Testis attached to gubernaculum and runs all the way to —–
Gubernaculum shortens and testes descend, behind processus vaginalis. Pushes through anterior abdominal wall, the deep inguinal ring, through abdominal wall and out into the scrotum though the superficial inguinal ring.

Question 24

Outline the descent of the ovary

Answer 24

Gubernaculum attaches ovary inferiorlyto labioscrotal folds. Ovary descends to the pelvis, and is prevented from descending further by mechanical blockage of uterus. Gubernalculum becomes round ligament of the uterus, and runs through inguinal canal.