NondisjunctionNondisjunction

Nondisjunction—When chromosomes fail to separate during meiosis.

This can happen at anaphase I or II.

Human Human male male karyotypkaryotype, e, written written

as as 46 46 XYXY

Human Human female female karyotypkaryotype, e, written written

as as 46 46 XXXX

Down SyndromeDown Syndrome47, XX or XY, +21

1 in 700 births

47 chromosomesXY or XX

#21 Trisomy Nondisjunction

Down Syndrome

Down SyndromeDown Syndrome

Short, broad hands Stubby fingersMentally retardedSmall round faceProtruding tongueShorter lifespanSlanted eyes

Patau Patau syndromesyndrome

47, XX or XY,Trisomy 13

Patau’s Trisomy Patau’s Trisomy SyndromeSyndrome

1 in 10,000 births

47 chromosomesXY or XX

47, +13

#13 Trisomy Nondisjunction

Small headSmall or missing eyesHeart defectsExtra fingersAbnormal genitaliaMentally retardedCleft palateMost die before birth; some survive a few weeks after birth

Patau’s Trisomy Patau’s Trisomy SyndromeSyndrome

Edwards SyndromeEdwards Syndrome

47, XY, +18

Edward’s Trisomy Edward’s Trisomy SyndromeSyndrome

1 in 2500 pregnancies, 1 in 6000 births

47 chromosomesXX=80%

XY=20%

#18 Trisomy Nondisjunction

Edward’s Trisomy SyndromeEdward’s Trisomy Syndrome

Small headMentally retardedInternal organ abnormalities90% die before 5 months of age

JacobJacob’’s syndromes syndrome

XYYNo abnormal

appearance/behaviorfertile

Jacob’s SyndromeJacob’s Syndrome

1 in 1,000 boys

47 chromosomesXYY only

#23 Trisomy Nondisjunction

Jacob’s SyndromeJacob’s Syndrome

Normal physicallyNormal mentallyAssociated with risk of learning disabilities.Once thought to be more aggressiveNormal lifespan

KlinefelterKlinefelter’’s Syndromes Syndrome

XXY, male

Klinefelter’s SyndromeKlinefelter’s Syndrome

1 in 500-1000 births

47 chromosomesXXY only

#23 Trisomy Nondisjunction

Klinefelter’s Klinefelter’s SyndromeSyndromeScarce beardLonger fingers and armsSterileLow testosteroneDelicate skinPossible learning disabilitiesNormal lifespanMore X chromosomes could cause worse symptoms (XXXY)

Turner SyndromeTurner Syndrome

45, X

Turner SyndromeTurner Syndrome

Occurs in about 1 in 2,500 birthsMany do not survive to birthNo menstruationNo breast developmentNo hipsBroad shoulders and neck

Trisomy XTrisomy X47 XXX symptoms

healthy and fertile - cannot be distinguished from normal female except by karyotype

Triple X SyndromeTriple X Syndrome

1 in 1,000 births

47 chromosomesXXX only

#23 TrisomyNondisjunction