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Flashcards in Control of sex determination Deck (18)
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1

Outline Gonad formation

-The urogenital ridge divides into the nephrogenic ridge and the gonadal ridge
-The nephrogenic ridge develops into the mesonephric ducts or Wolffian ducts& the precursors of the urinary system
-The paramesonephric ducts or Mullerian ducts develop from further invagination of the intermediate mesoderm
-The primordial germ cells migrate to the gonadal ridge which develops into the gonads

2

What drives testicular differentiation ?

-SRY expression

3

Outline male sex differentiation

-Wolffian ducts persist-male internal reproductive organs
-Male external genitalia
-Development of male secondary sexual characteristics
-Spermatogenesis

4

Outline female sex differentiation

-Mullerian ducts persist-female internal reproductive organs
-Female external genitalia
-Development of female secondary sexual characteristics
-Ovulation & fertility

5

What does formation of the bipotential gonad depend on?

-A number of transcription factors

6

Explain gonad determination

- Formation of the ovary/testes from the bipotential gonad
-The presence of a Y chromosome leads to testes formation
-likely to be a testes determining factor on the Y chromosome

7

Outline the formation of the testes involving SOX9 and DAX1

SOX9:
-Gene on chromosome 17
-Acts on downstream targets to promote development of the testes
-Dosage sensitive
DAX1 (orphan nuclear receptor)
-Gene on X chromosome
-Represses testes development
-Dosage sensitive
-Duplications lead to DSD in XY individuals

8

What is the role of the anti-Mullerian hormone ( AMH) in Gonadal formation

-AMH leads to regression of the mullerian structures
-Testosterone promotes the development of the Wolffian duct into the epididmis, vas deferens and seminal vesicles

9

What happens to testosterone in the presence of a testis?

-Testosterone is converted to the more potent androgen Dihydrotestosterone ( DHT)
-DHT promotes the development of the genital tubercles, labioscrotal folds& urogenital sinus into the penis, scrotum& prostate

10

What occurs in the absence of AMH

-The Mullerian duct develops into the fallopian tubes, uterus& upper vagina (NOTE, NOT THE WHOLE OF THE VAGINA)
-The Wolffian duct regresses

-The genital tubercles, labioscrotal folds& urogenital sinus develop into the lower vagina, vulva clitoris
-These processes are not dependant on the presence of a functional ovary

11

Which hormone is involved in Mullerian duct formation

Estrogen

12

Is Wolffian duct regression active or passive

Passive

13

If Mullerian duct regression active or passive

Active, involves AMH( which is produced by the testis)

14

Outline Klinefelter syndrome

Karyotype, 47 XXY
Clinical features:
-Normal at birth, higher incidence of undescended testes
-Tall stature
-Small 'pea-sized' testes
-Lack of secondary sexual characteristics
-Gynaecomastia
-Infertility
-Some behavioural and minor learning disabilities

15

What is the function of DAX1 in development of Klinefelter syndrome

-The factor DAX 1 is located on the X chromosome and is dosage sensitive
-Here there are 2 X chromosomes so the guy has 2 copies of DAX 1 and cos DAX 1 regresses the function of the SRY gene; that is why these problems result with Klinefelter's syndrome

16

How can DSDs arise from a region of a chromosome

-SRY translocations
-Chromosomally: still looks like XX but has this vital SRY gene on it so testis produced therefore testosterone and AMH are produced
-Present after puberty with short stature, gynaecomastia, small testes, fertility issues
-Male gender indentity
-Treated with testosterone

17

How can disorders of sexual development ( DSDs) arise?

From variation at the level of:
-A whole chromosome
-The region of a chromosome
-A change within a single gene

18

How can DSDs arise from a change within a single gene ?

-5 alpha reductase deficiency. This is the enzyme involved in the conversion from testosterone to the male potent androgen DHT
-Internal structures male
-Variable appearance of external genitalia at birth
-During puberty increased androgen levels lead to virilisation of external genitalia
-The tissues of external genitalia start to change around puberty
-Others may have genitalia that appear predominantly male, often with an unusually small penis (micropenis) and the urethra opening on the underside of the penis (hypospadias).