Lec 12: Intro to Chromosomal Disorders

Question 1

What are the 2 types of chromosomal disorders?

Answer 1

Numerical and structural chromosomal disorders

Question 2

What are the craniofacial, limb, and heart abnormalities associated with Down’s Syndrome?

Answer 2

Brachycephalic, epicantal folds, upward slanting palpebral fissures, protruding tongue
Limbs: single palmar crease, small middle phalyx of 5th finger, gap between first and second toe
Heart: atrial and ventrcular defects, common atrioventricular candal, patent ductus arteriosis

Question 3

What does trisomy 13 result in, and what is it also known as?

Answer 3

Also known as Patau Syndrome

• poor postnatal survival
• brain, microphthalmia, and hypotelorism or cyclopia
• bilateral cleft lip and palate
• extra digits
• truncus arteriosus and tetralogy of Fallot

Question 4

What percentage of trisomy 13 cases die in utero? What about trisomy 18?

Answer 4

Trisomy 13 (Patau's syndrome) 98% die in utero
Trisomy 18 (Edwards syndrome) 95% die in utero

Question 5

Deletion of what chromosome results in cri du chat syndrome? What are the symptoms?

Answer 5

deletion in chromosome 5

• high pitched cat cry (malformed larynx)
• intellectual disability
• delayed development
• small head size
• low birth weight
• weak muscle tone

Question 6

Deletion of what chromosome results in Wolf-Hirschhorn syndrome? What are the symptoms?

Answer 6

Characteristic facial appearance, broad flat nasal bridge and high forehead

• delayed growth
• intellectual disability
• seizures
• 85-90% are not inherited, due to de novo mutations. 10% are ring chromosomes or translocation

Question 7

What type of chromosome is the X chromosome? The Y chromosome? (metracentric, submetacentric, or acrocentric)

Answer 7

X is submetacentric

Y is acrocentric

Question 8

How do X and Y chromosomes pair in male meiosis?

Answer 8

The tips of the p arm on Y and X chromosomes pair up in a region that allows for homologus recombination called the pseudoautosomal region (PAR1)

Question 9

Where are the pseudoautosomal regions on the X and Y chromosomes and what do they allow?

Answer 9

PAR1 is on the p arm and is where crossover occurs

PAR2 is on the q arm of both chromosomes

Question 10

What covers the Xi chromosome to create the Barr body?

Answer 10

XIST which is expressed by the X inactivation center (XIC)

Question 11

What does the Xa express that is opposite to the XIST?

Answer 11

TSIX that binds and inactivates XIST and XIC