karyotyping lab

8/4/2019 Karyotyping Lab

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Chromosomes and Karyotyping

Dr. Nisrine Bissar-Tadmouri


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Chromosomes

Karyotype:display of

chromosomes

paired according

to their size,location of the

centromere, and

staining patterns.

organized into 7groups


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Cytogenetics

a discipline that matches phenotypes with detectable

chromosomal abnormalities.


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Malekaryotype


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Trisomy 21or

Downs

Syndrome


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Submetacentric

Metacentric

Acrocentric


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Diagnosis of chromosome abnormalities

Child born

take blood and look at lymphocytes

Unborn child

Prenatal DiagnosisChorionic villus sampling (CVS)

Amniocentesis (AF)

Fetal Blood Sampling (FBS)1) Karyotype

2) FISH: Fluorescent in situ Hybridization


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Indications for Karyotyping

An individual with characteristics of one of thecommon chromosomal syndromes (Downs,

Turners, kleinfelter etc..)

The presence of multiple congenital anomalies(usually associated with mental retardation)

A couple with multiple miscarriages

An individual at risk for inheriting ortransmitting a chromosomal rearrangement

(translocation)

A child with ambiguous external genitalia


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http://upload.wikimedia.org/wikipedia/commons/5/57/FISH_%28Fluorescent_In_Situ_Hybridization%29.jpg


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Downs syndrome

FISH is used for fine

details like

submicroscopic

deletions, or even genelevel mutations

(hard to detect on the

Karyotype)


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Screening

Both in first and second trimester

Maternal serum screening

Ultrasound

Indicates which should go forward for invasive

procedure


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Human Karyotype preparation for prenatal diagnosis

10-12 weeksAround 16

weeks


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How to prepare a chromosome spread


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sample

0.7 ml heparinized blood

10ml cell growth medium containing

phytohemagglutinin (mitogen)

Incubate 72 hrs at 370C


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synchronization

100 ml colcemid

Incubate for 20 min at 370C


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Cell collection

Centrifuge at 1200 rpm for 10 min

Remove medium leaving 0.5 ml


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swelling

Resuspend cells in the remaining medium

Add 2 ml of 0.075M KCl drop by drop

Add 8 ml of the KCl solution

Incubate for 15 min at 370C


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fixation

Centrifuge and remove supernatant

Resuspend cells and add 10 ml freshly prepared fixative

(methanol: glacial acetic acid, 3:1) for 10-15 min

Centrifuge and remove supernatant


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Metaphase spread

Resuspend in small amount of fixative

Drop suspension on microscop slide

Stain by immersing in Giemsa stain 7-10 min


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Writing karyotype information

Abbreviation What it means

46, XY Normal male

46, XX Normal female

45, X Turner syndrome female

47, XXY Klinefelter syndrome male

47, XYY Jacobs syndrome male

46, XY del (7q) Male missing part of long arm of chromosome 7

47, XX+21 Female with trisomy 21

46, XY t (7;9)

(p21.1;q34.1)

Male with translocation between short arm of

chromosome 7 band 21.1 and long arm of chromosome

9 band 34.1


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Writing karyotype information

Abbreviation What it means

46, XX, del(5)(p15.3) Cri du Chat syndrome female

46, XY, dup(21)(q21) Male with duplication of band q21 on chr 21

45, XX, inv(9)(p12q13) Female with percentric inversion on chr 9

46, XX,del(15)q12 Female with Prader-Willi

46, XX/45,X0 A mosaic case of Turner Syndrome

karyotyping lab

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