q5 - step1mom

[ArchivalUser]

A 4-month-old female is brought to her pediatrician
by her mother who is concerned about
some photographs she recently had developed.
In the photographs, only the child™s right eye
demonstrates a red reflex. Examination of the
left eye confirms absence of a red reflex.
Which of the following mechanisms is most
likely involved?
(A) Deletion in the long arm of chromosome
13
(B) Deletion in the short arm of chromosome
5
© Deletion of the short arm of chromosome
11
(D) Nondisjunction of chromosome 18
(E) Nondisjunction of chromosome 21

[ArchivalUser]

chromosome 11 (aniridia ?),
Chromosme 13 = Patau Syndrome,
Chromsme = Cru di Chat,
Chromosme 18=Edwards,
Chromosme 21=Down's Syndrome

[ArchivalUser]

(A) is correct. Retinoblastoma is the result of inherited
or acquired deletions of the retinoblastoma tumor
suppressor gene on the long arm of chromosome 13.
The tumor arises most frequently in the first 2 years of
life with leukocoria, absence of the red reflex, poor
vision, or squint.
Explanation B: No. Deletion in the short arm of
chromosome 5 results in cri du chat syndrome.
Explanation C: No. Deletion in the short arm of
chromosome 11 results is aniridia (congential absence
of the iris) and is associated often with Wilm™s tumor.
Explanation D: No. Nondisjunction of chromosome 18
results in trisomy 18 (Edward™s syndrome).
Explanation E: No. Nondisjunction of chromosome
21 during the first meiotic division results in Down™s
syndrome.