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