1c. Sex chr abn

Question 1

Inactivation occurs in week …..of embryo (100 cells)

Answer 1

1

Question 2

if Y chr is present in Turner, increased risk of……

Answer 2

gonadoblastoma

Question 3

In balanced X translocations, normal X is……(active/inactive)

Answer 3

Inactive

Question 4

What are the critical regions of X and Y?

Answer 4

Question 5

What are the potential phenotypes for the following deletion abnormalities?

• 46,X,del(X)(q_)
• 46,Y,del(X)(q_)

Answer 5

Chr X del q: inactivation of delX, fewer turner features, ovarian failure

Chr Y del q: large deletions are lethal as there is no other copy

Think about the diagram

Question 6

What are the potential phenotypes for the following duplication abnormalities?

46,X,dup(X)(p_):
46,Y,dup(X)(p_):

46,X,dup(X)(q_):
46,Y,dup(X)(q_):

MCR: multiple congenital abn
MR: Mental retardation
DSS: Dosage sensitive sex reversal

Answer 6

X dup in female: 46,X,dup(X)(p_):variable phenotypes: normal to Turner syndrome features; amenorrhea to normal fertility

X dup in male: 46,Y,dup(X)(p_): * Xp21.2 to p22.2 phenotypic females with MCA, MR* DSS locus - dosage-sensitive sex reversal = DAX1= NR0B1

46,X,dup(X)(q_): normal phenotype
46,Y,dup(X)(q_): MCA, MR due to functional disomy

Question 7

What is the most common abnormal X?

Answer 7

46,X,i(X)(q10)

Question 8

Why ring chrs are usually mosaic?

Answer 8

Rings are unstable