Sex determination

Question 1

State the 3 states of sex determination

Answer 1

1. gonad formation 2. gonad determination 3. Sex differentiation

Question 2

Describe the stage of gonad formation

Answer 2

Undifferentiated gonadal ridge developed into a bipotential gonad due to several transcriptional factors.

Question 3

Describe the stage of gonad determination

Answer 3

If no Y chromosome present, ovary developes. If Y chromosome is present, the SRY gene causes differentiation. Sox 9 is also an important gene (not on Y chromosome) and is necessary for formation of testes. Both are crucial to testes developement.

Question 4

Describe DAX1 role in gonad determination

Answer 4

DAX1 supresses testes development.

Question 5

Describe requirements for the formation of ovaries

Answer 5

• germ cells
• two X chromosomes
• presence of transcriptional factor Wnt4.

Question 6

Describe the process of sex differentiation in males and females

Answer 6

Question 7

Describe the action of testosterone and AMH (anti mullarian hormone) on further male sec developement

Answer 7

testosterone is converted to dihydrotestosterone (more potent) which promotes the developement of penis, scrotum and prostate.

AMH supresses developement of AMH

Question 8

Describe the further developement of female genetialia

Answer 8

in the absence of testosterone, wolffian duct passively regresses. External and internal genitalia developes from mullarian duct.

Question 9

Define the components of the combined pregnancy test

Answer 9

• maternal age
• nuchal translucency (ultrasound)
• PAPP-A levels (high if risk)
• B-hCG levels (high in T21 and low in T13/18)

Question 10

State the difference between NIPT and NIPD tests

Answer 10

Non- invasive prenatal diagnosis looks for markers not normally present in maternal blood to diagnose diseases. NIPT just looks at levels of certain chromosomes overall to see if there is an abnormality in the fetus (screening not diagnosis).

Question 11

Desribe maternal serum screening

Answer 11

Alpha Foeto Protein is measured through the placenta, amnioti fluid or vasculature in uterus.

Levels of protein can predict neural tube deffects by lookin at their levels at a specific point in the pregnancy.

Question 12

Describe chorionic villus sampling

Answer 12

Sampling of the chorionic villi in the placenta for DNA analysis and metabolic investigations.

Question 13

Describe amniocentesis and when it can be done

Answer 13

10 - 20 ml of amniotic fluid sampled. Cells are cultured and can be analysed for DNA of buichemical studies