L15 Chrom Abn Flashcards
LO2: concept of karyot
-chrom anal- study metaph chroms. Req source of liv cells for in vitro growth. Cells cult, accum at metaph, harvested.
Stew proc, can be weeks- spindle inhibitor eg colcemid. Hypotonic eg KCl. Fixative 3:1 methanol: acetic ac. Slides prep and stained with geimsa stain. LM.
-metaph chroms- count chroms, check all pairs present and banding same for each pair.
Specif types:
BM 0-1d cult grown susp.
Blood t lymphoc 2-3D cult, grown in susp.
Amn fluid 7-21d cult, grown on substr in tiss cult flask.
CVS chorionic villus- 7-21d, grown on substr.
Sol tiss 7-21d, grow on substr.
Diff samps- chrom diff lengths. Blood long, good G band patt. AF less resol. BM has G band but much shorter.
Always count, check pairs, check banding. For delet/insert. Qual scores for diff samps.
-chrom anal- systematic sorting of chroms=karyot. Metaph chrom stained, paired, grouped. abnorms desc using stand ISCN nomenclature 2013. Karyot can be prod by cut and paste chrom pics into systematic organised set metaph chroms in pairs, chrom 1 top L, sex chroms bott R.
-chrom morph- p and q arms. Metacentric. Submetacentric- shorter p. Afrocentric- predom q, v short p not cont any euch mater so no genes of imp.
-chrom grps- acc to size nd shape. Grps A-G. D and G are acrocentric chroms with satellites on p arms. 22 bigger than 21. X consid C grp, Y G grp.
-staining meths- G banding. Metaph exposed to trypsin- dig prots differentially. Stain with romanowski type dye- leishman, geimsa. Prod dark and light bands- dark G pos, AT rich, gene poor. Light G neg, GC rich, gene rich.
Pairs grouped, right orient, size order.
-chrom ideograms- stand band patt for each chrom. Dark and light bands numb acc to ISCN. To desc chrom abn, each chrom own bands in p and q.
-staining meths-
Solid stain.
G banding.
C banding- pref stain heteroch at centromere and 1, 9, 16, Yq. Also allows asses gen size of centroms- made of alpha sat DNA does vary, can be norm.
Q band- Yq var, Fluor tech.
Replic- active/inactive X.
-automated karyot- expens, time cons. AutoM/semi automated sys. Slides scanned automatically. Metaph images taken. Digit karyot said form images- cut out chroms. Anal paired chroms on screen.
Uses- karyot, FISH, scan platform, metaph finding, spot count, LGH, M-FISH, flexib karyot.
LO1: expl how genet info in cell org as chroms.
-DNA wrap rnd histone octamer=2x H2A,3,4. 166bp. H1 stabils.
Higher order strucs stabil by loops of DNA on prot scaff= chromatin.
Active and inactiv chromatin- only exp if activ. Switch by epigenet modif. Meth and deacteyl= inactiv. Changes to hist NOT DNA seq.
LO3: recog, comprehend, and apply chrom nomenclature.
-stand karyot ISCN. Chrom numb, sex complem, struc changes. Sep by commas. NO spaces.
Eg 46,XX is norm fem. 47,XX,+21 is fem trisomy 21. 46,XYinv(7)(p11.2q11.23) is male chrom 7 inv break pt in both arms, segm btw inverted.
+1 foll by numb Indic extra/miss ent chrom. When piece chrom missing eg 5p- = missing segm. Del= delet. Dup. Inv. S=satellite. T=transloc.
LO4: outl reasons for refer pt for karyot
-why cytogentic anal?
Acc diag/ prog- Id synd, acc for phenot, acc for preg loss.
Better clinic management- eg horm therap bef puberty for klinefelter synd (XXY).
Asses fut repro risks- risk live born abn child, had abn child, had preg loss. Prev DS preg, 1% incr over pop risk of another.
Pre natal diag- TOP affected by preg/plan managem at birth.
-refer reasons-
Constit abn from birth- prenatal diag, birth defect, abn sex dev, insert, receurr fetal loss.
Acq abn- leuk: acute AML/ALL, chronic CML, myelodysplasia/myeloprolif disord. Solid tum. Specif transloc/abn can give prog info and conf diag and inform tx.
-pre natal diag meths-
CVS- 11-12wk gestalt, 1.2% misc, us transabdo, US guid.
Amniocentesis- 15wk, 0.8% misc, US. May serum screen for DS 15wk-biochem markers along with RFs and age. 1:150 OR (risk meas) offered PND.
1st trimester screen- us CVS. Biochem and US. Nuchal translucency and biochemistry markers. 1:150.
Fam hx of chrom abn.
Abn US- eg cystic hygroma neck, cleft palate, heart abn, limb abn.
DNA studies eg CF, SMA. Couples risk sing gene disord assess carrier status/fetus aff. Us CVS.
-birth defects- dysmorphism. Congenital malf. Ment retard. Dev delay (abn behav, learn diffic). Specif synd eg DS, williams synd (delet 7q11.23), DiGeorge synd heart defects (delet 22q71.2).
LO5: desc numeric and struc chrom abn and their sig.
NUMERICAL
NUMERICAL: polyploidy, aneuploidy.
Numeric cytogenetic abn-
-aneuploidy- loss/gain whole chrom. Due to err meiosis. Trisomies- 3 full viable at term eg trisomy 21, Patau synd +13, Edwards +18. Last 2 short surv if birth. Monosomies- only 1 full chrom loss viable eg turner synd 45,X fem only, viable as X inactiv.
-polyploidy- gain whole hap set chroms. Triploidy 3n eg 69, XXX (can’t get YYY). Most comm cause polyspermy-fert by more than 1 sperm. Triploidy occs in 2-3% prevs and 15% misc. term deliv rare and die fast. Tetraploidy rarer 1-2% but cells often fnd at pre natal diag as cult artef. Fail cell mem div. diploid/triploid mosaicism rare in live births.
-causes of aneuploidy- ori from non disj at a meiotic div. forms gametes with a miss chrom and extra chrom- which chroms inv affs viabil.
Can occ dur mitot div=mosaicism- 2 cell pops in an individual.
Non disj events can occ in meiosis and mitosis.
-non disj in meiosis- M1 both chroms to 1 daughter, us non viable cell lost. Then MII=gametes with 2 chromatids or none=zygote trisomy or monosomy. M2 both chromatids to 1 daughter , forms 2 norm gametes, 1 trisomy, 1 monosomy. Trisomy viable at 13,18,21.
-anaphase lag- chrom can be left behind at cell div if defec spindle func or att to chroms. Not incorp to daughter. Lagging chrom may be lost ent in meiosis or mitosis.
-trisomy 21- 1/650-1000. Hypotonia. Facial feats. Intell disab. Heart defec. Incr leuk. Incr early alz. 21q22 DSCR- critic reg. If band in marker chrom not full chrom 27 can= downs too.
-trisomy 18- Edwards synd. 1/6000 fem predom. Small lower jaw, promin occip, low ears, rocker bott feet, overlap fingers.
Mat M1 err us. Live 5-15 days modal. Most diag pre natal by scan.
-trisomy 13- Patau synd. 1/12000. Multip congenital abn. Polydactyly. Holopriosencephaly variab- 1 eye to cleft palate. Maj die neonate if reach term. Us diag anti natal.
-tuner synd- 45,X. Girls only. 1/25000. Puffy feet, redund neck skin, short stature, heart defec, mild learn diffic, neck Webb, infert.
Maj absent pat X- phenot diffs dep absent X ori. Pre natal see cystic hydroma.
LO5: NUMERIC X inactiv
- X inactiv- 1X active in cell. Fems inactiv 1=same X chrom complem active. Some genes esc.
- why 1X prob- X and Y short regs in comm at tips of p and q. =2 pseudo autos regs (PAR1+2)- Essen for pair dur meiosis. Turner pt monosomic for genes in PARs. Eg SHOX assoc short stature.
LO5: NUMERIC mosaicism
-presence 2+ cell lines in indiv- us due to mitot non disj. Through bod or tiss lins.
Deg deps on when non disj err occ-
1st post zyg div= no mosaicism, looks like meiotic event.
Subseq div= 3 cell lines, monosomy line us lost unless inv X.
Trisomy conceptus resc dur mitosis= mosaicism- anaphase lag. Losing addit chrom- revert to norm diploid count.
-1st post zyg div- monosomy cell line lost unless inv X. Other line all subseq trisomy.
Later mitot div- 2 norm cells, 1 trisomy, 1 monosomy lost. 47,+21/46,N mosaicism for DS,
LO5: NUMERIC uniparental disomy (UPD)
-homol chroms from 1 par.
Idiosomy- 2 identic chars? form 1 par.
Heterodisomy- 2 homol chrom from 1 par.
(These two dep on non disj at M1 or M2).
Segmental UPD- part of chrom inv.
Acq UPD- sol tum and leuk.
-UPD matters because of imprinting-
Imprinted chroms show differentiated exp of diff genes dep on par ori of chrom.
If chrom inv not imprinted, UPD no phenot eff. UPD sends for chrom 6,7,11,14,15,16. Diff phenot dep on mat/pat.
-prader willi mat. Angelman synd pat. Eff same reg on q arm chrom 15.
-Russel-silver (7). Beckwith weiderman pat (11).
-4 comm mechs gen UPD- trisomy resc most comm, also monosomy resc, gamete complemetation, mitot err.
Each req 2 Sep a abn events= rare.
-trisomy resc-
Meiosis- disomic gamete from meiotic err and monosomic gam= trisomic conceptus.
Post zyg mitosis- trisomy (mitot err) via los of 1 addit chrom forms UDP emb- 2 chroms from 1 par.
1/3 chance of creating UDP. Most comm mech, us heterodisomy.
-test for UDP- molec genet test. Using informative rep DNA markers on imprinted genes/regs of int. Show if Inher bi-par or not. If UDP conf, test id’s par ori and allow synd defin.
LO5: STRUC chrom abn.
-bal=exchange/rearr genet mater not cause miss/extra genes.
Unbal=struc chrom changes= miss/extra genet info.
