Test PPT 20140429

© 2009 NHS National Genetics Education and Development Centre Genetics and Genomics for Healthcare
www.geneticseducation.nhs.uk
Conditions caused by abnormalities in
chromosome structure
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Fig. 2.1 ©Scion Publishing Ltd
Child with 22q11 deletion. Note small mouth, narrow nose and upward slant of her eyes.

G-banded karyotypes of chromosomes
There is a balanced translocation. Chromosomes 1 and 22 have exchanged segments (arrows). The translocation
is described as 46,XX,t(1:22)(q25;q13)

How the 1;22 translocation originated
Chromosome 1 and 22 broke at the positions indicated by the arrows, and the cell’s DNA repair machinery
rejoined the ends to form the two derivative chromosomes as shown. The derivative chromosomes are labelled
der(1) and der(22).

G-banded karyotype
She has inherited a normal chromosome 1 but her translocated chromosome 22 (arrow). She is trisomic for the
portion of chromosome 1 distal to 1q25, the translocation breakpoint, and monosomic for chromosome 22 distal
to 22q13.

A Robertsonian translocation
The inset shows how this common type of chromosome abnormality arises. The short arms of all the acrocentric
chromosomes (13, 14, 15, 21, 22) contain similar DNA. Inappropriate recombination between two non-
homologous chromosomes produces the fusion chromosome, which functions as a normal single chromosome
in mitosis. The small acentric fragment comprising the two distal short arms is lost.

During meiosis I matching chromosome segments pair.
If one chromosome has an inversion compared to its
homolog, they usually form a looped structure.

Fig. Disease box 3 ©Scion Publishing Ltd
(a-c) Reproduced with permission from Dr Ursula Bellugi, The Salk Institute for Biological
Studies.
(a) “Williams-Beuren syndrome” (b) “Drawings by people with Williams-Beuren syndrome”

Photos courtesy of Dr Bert de Vries
A child with multiple congenital abnormalities suggestive of a chromosome abnormality
She has severe mental retardation, growth retardation, microcephaly and dysmorphism of the face and hands
(epicanthic folds, hypertelorism, arched eyebrows, low-set ears, short philtrum, open mouth appearance, full
lips, irregular position of the lower teeth, clinodactyly of the 5th
finger and distal brachydactyly).

Example of array-CGH output

22q11 metaphase FISH
The green spots are a control probe, used to identify the two copies of chromosome 22 and confirm that
hybridization has taken place. The red spots are the TUPLE1 probe. Only one of the two copies of chromosome
22 contains the sequence that hybridizes to this probe.

The 15q11q13 deletion in Prader-Willi or Angelman syndrome patients is sometimes just visible under the
microscope in a standard cytogenetic preparation. In most cases a molecular test (FISH or PCR) is needed to
make the diagnosis.

Photo. courtesy of Dr John Yin
Typical appearance of acute lymphocytic leukaemia. Small blasts with high nuclear – cytoplasmic ratio, some
with prominent nucleoli.

Reproduced from Molecular Cancer, 2: 30; © 2003 Duensing et al.; licensee BioMed Central Ltd
Burkitt’s lymphoma
(a) Histology, and (b) a karyotype showing the characteristic 8;14 translocation. Additional chromosome
abnormalities are also present, as is usually the case in neoplasia.

Photo. courtesy of Dr Christine Harrison
Metaphase with TEL-AML1 fusion
The green signal is on the normal chromosome 12, one red signal is in the normal chromosome 21 and one is on
the derived chromosome 12. The yellow TEL-AML1 fusion signal is on the derived chromosome 21.

45,XX,der(14;21)(q10;q10)

46,XX,t(4;15)(q2?1.3;q13)

46,XX,t(9;22)(q34;q11)

ish der(9)(ABL-),der(22)(BCRsp+conABLsp+,ABLsp+,BCRsp+)

46,X,r(X)

ins(22;9)(q11;q13q34)

46,XY.ish del(15)(q11.2q11.2)(SNRPN-)

46,XX.ish del(22)(q11.2q11.2)(TUPLE1-)

46,X,del(X)(p21.1)

46,XX,del(4)(p15.2p16.?2)

ish del(7)(q11.23q11.23)(ELN-)
Williams syndrome

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