PHYSIOLOGY - Sex Determination and Development of Reproductive Organs

Question 1

During early embryonic development, what is the name of the gonads before sex determination occurs?

Answer 1

Indifferent gonads

Question 2

In higher mammals, what are the allosomes which determine female and male individuals?

Answer 2

Female: XX
Male: XY

Question 3

Which gene on the Y chromosome plays an important role in sex determination?

Answer 3

Sex determining region on the Y chromosome (SRY)

Question 4

Describe the pathway of sex determination in the mammalian female

Answer 4

Wnt4 activates β-catenin which along with FOXL2 inhibits SOX9 gene expression, stimulating the indifferent gonad to develop into an ovary

Question 5

Describe the pathway of sex determination in the mammalian male

Answer 5

WT1, FOG2 and GATA4 activate the SRY gene which promotes SOX9 expression, stimulating the indifferent gonad to develop into a testis

Question 6

In birds and snakes, what are the allosomes which determine female and male individuals?

Answer 6

Female: ZW
Male: ZZ

Question 7

What is the gene present on the Z chromosome which has the gene dosage affect in sex determination in birds?

Answer 7

DMRT1 gene on the Z chromosome

Question 8

Describe the pathway of sex determination in male birds compared to female birds

Answer 8

Male birds have ZZ allosomes which each express DMRT1 genes which promote the expression of SOX9 and stimulate the indifferent gonad to develop into a testis. Female birds have ZW allosomes so only the single DMRT1 gene is expressed which is not enough to promote SOX9 expression, so the indifferent gonad develops into an ovary

Question 9

How does sex determination differ in reptiles and amphibians?

Answer 9

Reptiles and amphibians have no allosomes and instead the temperature of the egg determines the sex of the offspring (cold nest results in female offspring, warm nest results in male offspring)

Question 10

What are the two methods of sex determination in fish?

Answer 10

Fish have XX and XY allosomes as well as temperature regulation methods involved in sex determination

Question 11

During early embryonic development, what do the gonads develop from?

Answer 11

Mesonephros

Question 12

What are primordial germ cells?

Answer 12

Primordial germ cells are the embryonic precursors of the gametes

Question 13

Where are primordial germ cells produced before migrating to the indifferent gonad?

Answer 13

Primordial germ cells are produced in the yolk sac and migrate to the indifferent gonads to proliferate

Question 14

Why do the female germ cells undergo meiosis in the foetal gonad but the male germ cells do not?

Answer 14

Due to the cyp26b1 enzyme produced by the foetal testes which inhibits vitamin A, preventing the male germ cells from entering meiosis

Question 15

Which of the embryonic ducts persists in the male?

Answer 15

Mesonephric duct

Question 16

Which of the embryonic ducts persists in the female?

Answer 16

Paramesonephric duct

Question 17

Which internal structures are formed from the mesonephric duct?

Answer 17

Epididymus, Vas deferens, Rete testis

Question 18

Which internal structures are formed from the paramesonephric duct?

Answer 18

Oviducts, Uterine horns, Uterine body, Cervix, Cranial vagina

Question 19

What do the foetal testes produce which allows the mesonephric duct to persist in the male?

Answer 19

The foetal testes produce testosterone which stabilises the mesonephric duct and AMH (Antimullerian hormone) which degenerates the paramesonephric duct

Question 20

What is essential for the development of the male external genitalia?

Answer 20

Androgens (testosterone)

Question 21

How do androgens (testosterone) lead to the development of male external genitalia?

Answer 21

5α-reductase enzyme acts to metabolise testosterone into the DHT metabolite which acts on androgenic receptors to ‘masculinise’ the external genitalia

Question 22

Describe how the penis is formed due to the presence of androgens (testosterone)

Answer 22

In the presence of testosterone, the urogenital fold will fuse to close the urogenital orifice allowing the urethra to extend to the distal end of the genital tubercle which forms the penis

Question 23

Describe how the female external genitalia is formed?

Answer 23

In the absence of androgens (testosterone), the urogenital orifice remains open and the genital tubercle forms the clitoris

Question 24

What is Hypospadias?

Answer 24

Hypospadias is a congenital condition in males in which the urethral orifice forms on the ventral surface of the penis due to a lack of androgens during embryonic development