Sex-Differentiation

Question 1

What is the sex-determining region of the Y chromosome?

Answer 1

SRY gene

Question 2

At which point is genetic sex determined?

Answer 2

Fertilisation, depends on the sperm.

Question 3

In humans, which type of sex are males and which type are females?

Answer 3

Males are heterogametic (XY)

Females are homogametic (XX)

Question 4

What term is used to describe the Y chromosome because it is small and has lots of heterochromatin and doesn’t carry many genes?

Answer 4

Transcriptionally quiet

Question 5

What term is used to describe SRY because it is the same in many species?

Answer 5

Conserved sequence.

Question 6

What is the condition called where the genotype is female (XX) but the person develops as a male, and what causes it?

Answer 6

XX sex reversal, there has been translocation of the SRY box onto the X chromosome.

Question 7

What is the condition called where the genotype is male (XY) but the person develops as a female, and what causes it?

Answer 7

XY sex reversal, the SRY gene on the Y chromosome is missing or mutated.

Question 8

What do the gonads develop from in the foetus?

Answer 8

Genital ridge primordia (bipotential structures)

Question 9

What do the genital ridge primordia develop from on either side of the central dorsal aorta?

Answer 9

Mesenchymal knots.

Question 10

What is the first wave of migrating cells into the genital ridge primordia?

Answer 10

The primordial germ cells (which do not express SRY) migrate from where they form in the yolk sac, through the cloaca, and into the genital ridge primordial.

Question 11

Where in the genital ridge primordia do the PGCs migrate into in the male, and where in the female?

Answer 11

In the male they migrate into the medulla and the cortex degenerates. In the female they migrate into the cortex and the medulla degenerates.

Question 12

What is the second wave of migrating cells into the genital ridge primordia?

Answer 12

Coelomic/germinal epithelial cells (which express SRY in the male) migrate into the genital ridge primordia as primitive sex chords.

Question 13

What happens to the coelomic epithelial cells in the male?

Answer 13

They proliferate vigorously and project deep into the medulla. They surround the PGCs to form testis cords which are the precursors of seminiferous tubules. The coelomic epithelial cells form pre-Sertoli cells, and the PGCs they surround form prospermatogonia.

Question 14

What happens to the coelomic epithelial cells in the female?

Answer 14

The coelomic epithelial cells don’t express SRY so the primitive sex cords are ill-defined and don’t project far into the genital ridge. Instead, the coelomic epithelial cells condense cortically and surround the PGCs in small clusters to form primordial ovarian follicles. The coelomic epithelial cells will form granulosa cells and the PGCs form oogonia and then eventually oocytes.

Question 15

What is the third wave of migrating cells into the genital ridges?

Answer 15

Mesonephric cells from the mesonephric primordia (don’t express SRY).

Question 16

What 3 things do mesonephric cells contribute to in the male?

Answer 16

Leydig cells between the testis cords to produce androgens.
Vascular tissue of the testes.
Myoid cells, which form the tubules of the rete blastema and rete testis.

Question 17

What two things do mesonephric cells contribute to in the female?

Answer 17

Vascular tissue

Thecal cells, which cluster around the developing primordial follicles

Question 18

What is the function of SRY?

Answer 18

To act as a transcription factor and activate the transcription of SOX-9.

Question 19

What are 5 functions of SOX-9?

Answer 19

Stimulates the production of prostaglandin-D2 by the pre-Sertoli cells
Activates transcription of more SOX-9
Inhibits the FoxI2 gene to stop theca cells and vascular tissue being formed so ovaries aren’t formed
Activates production of Fibroblast Growth Factor 9
Stimulates production of anti-Mullerian hormone

Question 20

What does prostaglandin-D2 do?

Answer 20

Stimulates SOX-9 production in neighbouring Sertoli cells.

Question 21

What does Fibroblast Growth Factor 9 do?

Answer 21

Promotes SOX-9 production

Acts as a chemotactic factor for the 3rd wave of migrating cells (mesonephric cells)

Question 22

What does a defect in the SOX-9 gene cause?

Answer 22

Production of ovo-testes.

Question 23

What happens to the cell division of PGCs in foetal testes?

Answer 23

After being enclosed in the developing sex cords, they cease mitosis and enter a long period of mitotic arrest, until puberty when mitosis is reactivated.

Question 24

What happens to the cell division of PGCs in foetal ovaries?

Answer 24

The oogonia cease meiosis and enter the first meiotic division to produce all the primary oocytes a woman will ever have.
The primary oocytes are encased in primordial ovarian follicles by condensation of the granulosa cells from the invading sex cords.

Question 25

Which duct produces the male reproductive tract, and which produces the female reproductive tract?

Answer 25

Mesonephric/Wolffian duct produces the male reproductive tract. Paramesonephric/Mullerian duct produces the female reproductive tract.

Question 26

Which two hormones are essential for male development, and what are their functions?

Answer 26

Androgens produced by Leydig cells - cause the mesonephric duct to remain and develop Anti-Mullerian Hormone produced by Sertoli cells - causes the paramesonephric duct to regress

Question 27

When do (phenotypic) secondary sexual characteristics begin to become visible?

Answer 27

At puberty, begin at gonadarche

Question 28

What are some phenotypic sexual characteristics of women?

Answer 28

``` Breast development Oestrous/menstrual cycle (cyclic changes in hormone levels and periodic egg production) Ovaries Oviducts, uterus, cervix, vagina Oocytes in small numbers ```

Question 29

What are some phenotypic sexual characteristics of men?

Answer 29

``` More continuous (not cyclical) reproductive processes Testes Vas deferens, seminal vesicles Spermatozoa in vast numbers Musculature Deeper voice More likelihood of baldness Androgenous hair patterning. ```

Question 30

What does perinatal exposure to androgens result in?

Answer 30

The hypothalamus being insensitive to oestrogen later in life, so being functionally male.

Question 31

What is Turner's syndrome, and what are the characteristics?

Answer 31

Unpaired X chromosome (X0) due to nondisjunction. Ovaries present but underdeveloped female reproductive tract, breasts underdeveloped, infertility, amenorrhea, small stature, nevi (brown spots on skin), fold of skin in the neck.

Question 32

What is Klinefelter's syndrome?

Answer 32

Genotype XXY. Testes present but underdeveloped, infertile, tall stature, breast development, testicular atrophy, osteoporosis.

Question 33

What is Androgen Insensitivity Syndrome?

Answer 33

The intracellular androgen receptors are absent, or a mutation has altered their structure, so androgens are secreted by the testes but the target tissues fail to respond.

Question 34

What are the characteristics of Androgen Insensitivity Syndrome?

Answer 34

Genotype XY but phenotypically female and infertile. No internal genitalia, as AMH is produced which degenerates the paramesonephric tract, but androgens can't rescue the mesonephric tract, testes are present.

Question 35

What is guevedoces?

Answer 35

Penis at 12. A form of Androgen Insensitivity Syndrome which is due to a deficiency in the enzyme 5-alpha reductase, which causes the XY person to appear phenotypically female until puberty. The increase in androgen production after puberty overcomes the tissue insensitivity, the clitoris expands into a penis, the testes descend, and the person begins to function as a normal male.

Question 36

What is congenital adrenal hyperplasia?

Answer 36

When the genotype is XX but both the paramesonephric and mesonephric ducts are retained due to the hyperactive foetal adrenal glands trying to overcome the low production of corticosteroids. The person will have external male genitalia.

Question 37

What is the difference between sex and gender?

Answer 37

Sex is determined by your chromosomal make-up, gender is a result of a combination of genetics and environment, and is usually decided at birth based on your external genitalia.