Genetics (conditions)

Question 1

X-inactivation

Answer 1

• Occurs randomly
• 2 weeks post-fertilisation
• Same X remains active/inactive
• Sex chromosome trisomies and monosomy X tend to be more tolerated
• Begins at X-inactivation centre
• RNA transcript here is called “X-inactive specific transcript” (Xist) and it coats X chromosome leading to inactivation
• inactivated X chromosome condenses into compact structure called a Barr body

Question 2

Turner’s syndrome

Answer 2

No maternal age effect 
Absence of X chromosomes 
Human monosomy 
Short stature and infertility
coarctation of aorta- leading to systolic murmurs

Question 3

What is Triple X [XXX] syndrome?

Answer 3

Asymptomatic
Can be symptomatic- seizure, kidney abnormalities
47, XXX

Question 4

Klinefelter syndrome

Answer 4

47, XXY karyotype

associated with above average height and infertility

small testes, infertility, gynaecomastia

lack of secondary sexual characteristics (e.g. slim build; difficulty growing facial hair)

Diagnosis is by karyotype (chromosomal analysis).

Low LH and FSH