Cytogenetics Lesson 1

7/28/2019 Cytogenetics Lesson 1

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TheroleofCytogeneticsinthe

medicallaboratoryBHScinMedicalLaboratoryScienceCytogene5csCYT200A

Defini5on:

Cytogene5csistheanalysisofbloodor

bonemarrowcellsthatrevealsthe

organiza5onofchromosomes.Chromosomesarethephysicalstructures

thatcontainthegene5cmaterial,DNA.

Samplesbroughttothecytogene5cs

laboratoryarestudiedtoaidinthe

diagnosisofinheritedcondi5ons,andto

diagnoseormonitorcancercondi5ons

withassociatedchromosome

abnormali5es.

TheTimeLine:

Thedarkagespriorto192 2n=48

Thehypotonicera192 2n=46

ThetrisomyperiodLejeunedescribesDownsyndromeextrachr21

TheBandingeradifferen5alstaining

TheMoleculareraHigherresolu5on

screening

NeedtounderstandtheCellCycle

-Forculture--tounderstandgene5cabnormali5escausedduringcelldivision


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Mitotic inhibitor

arrests the spindle

formation and stopscell division at

metaphase:

Chromatin is theprotein-DNAcomplex in which

genetic material

exists in the

interphase nucleus.

During metaphase,chromatin

condenses into

chromosomes,which can be

stained andanalysed.


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NormalMaleKaryotype


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Blockstained

metaphaseandkaryotype


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Cytogenetics

Laboratory

Oncology SamplesHaematological and othersolid tumour cancers:

Bone marrow, blood samples,

tumour tissue, tumour effusion

Solid Tissue Samples

Recurrent miscarriagesCongenital abnormalities

Prenatal Samples

Increased Trisomy Risk(triple test)

Abnormal UltrasoundFamily history of chromosomeabnormality

Blood SamplesRecurrent MiscarriagesInfertilityFamily History of Chromosomeabnormalities

Ambiguous GenitaliaLearning difficulties and delayeddevelopment

Dysmorphic Features

Forensic SamplesVaried, for molecular analysis


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100

Mbp

10

Mbp

1

Mbp

100

Kbp

10

Kbp

1

Kbp

100

bp

10

bp

1

bp

SizeofAbnormality

Karyotyping


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100

Mbp

10

Mbp

1

Mbp

100

Kbp

10

Kbp

1

Kbp

100

bp

10

bp

1

bp

SizeofAbnormality

Karyotyping MLPA

FISH

ArrayCGH


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Spermatogonium

Primaryspermatocyte

Secondaryspermatocytes

4 spermatids

4 spermatozoa

Primary

oocyte

Oogonium

Secondaryoocyte

Polar Body I

Polar Body II

Meiosis Genetic variationthrough crossover

and

recombination


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Mitosis

Fetal period

Before or at birth

After birth

After puberty

At fertilization

Meiosis in progress

Arrested indiplotene

of Meiosis I

Meiosis I

complete

Arrest atMetaphase II

Meiosis IIcomplete

Oogonium

Primary Oocyte

Secondary Oocyte

& Polar Body I

Fertilized Ovum

& Polar body II

Females


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DifferencesinGametogenesis

Male

Puberty 60-6days 30-00mitoses 4sperma5ds 100-200million/

ejaculate

Female

Earlyembryonicdevelopment 10-0years 20-30 1ovumandpolarbodies 1ovum/menstrualcycle


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Parentaloriginofaneuploidy

Paternal% Maternal%

Trisomy13 1 8

Trisomy18 10 90

Trisomy21 9

4,X 80 20

47,XXX 9

47,XXY 4

47,XYY 100 0


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Downsyndrome

9%standardtrisomy 1%mosaics Duetoincreasein

maternalage

4%transloca5ons noageeffect


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Chromosomeabnormalitiesinmiscarriages

Incidence%

Trisomy13 2

Trisomy16 1

Trisomy18 3

Trisomy21

Incidence%

OtherTrisomy2

MonosomyX20

Triploidy 1

Tetraploidy

Other 10


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Chromosomeabnormalitiesinnewborns

Incidence/10,000births

Trisomy13 2 PatauSYndrome

Trisomy18 3 EdwardsSyndrome

Trisomy21 1 Downsyndrome

4,X 1 TurnerSyndrome

47,XXX 10 TripleXSyndrome

47,XXY 10 KlinefelterSyndrome

47,XYY 10

Unbalanced 10

Balanced 30

Total 90


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ChromosomeAbnormalities

Triploidy----rareatbirthlethal Trisomy16---mostcommoninspontaneousmiscarriages,

completelylethal.

Trisomy13&189%miscarry Trisomy2180%miscarry Klinefelters0%miscarry 4X1%atconcep5on.98%miscarry,mosaicsurvives


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Non-disjunctionduringmeiosis


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18


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19

DownSyndromekaryotype

46,XY,+21 (describes a pure trisomy


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20

q10

ISCN Nomenclature

Centromere

p arm

q arm

1. Number2. Sex3. Abnormality


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1. Identification ofa chromosome

by length andposition of thecentromere.

2. Accuratereporting ofabnormalities

(GPS coordinates)

3. The smaller thedefect, thelonger the

chromosomeneeds to be for

detection


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Cytogenetics: Application of ISCN Trisomy Information to Karyotyping:

Down SyndromePatau SyndromeEdwards Syndrome

Other than the established culture and karyotype of chromosomes wewill also cover some molecular techniques:FISH Fluorescent in situ hybridisation

PCR polymerase chain reaction

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Cytogenetics Lesson 1