Non-Disjunction Disorders

What are Non-Disjunction Disorders?!

Non-disjunction is a failure of chromosomes to separate properly (i.e there is an imbalance of genetic information)

Occurs when:

Homologous chromosomes fail to separate properly in Anaphase I

Sister chromatids fail to separate properly during Anaphase II

Having abnormal amounts of karyotypes will overload the cells, which may result in:

The death of the zygote

A person with a non-disjunction disorder being born

Key Terms Karyotypes

The number and visual appearance of the chromosomes in the cell nuclei of an organism or species

Trisomy

A condition in which a diploid organism has one more chromosome than usual.

47

Monosomy

An instance where there is only one chromosome is present, as opposed to the usual two

Human male karyotype, written

as 46 XY

Human female karyotype, written

as 46 XX

Autosomal Non-Disjunction

Refers to chromosome alterations in autosomes one through twenty-two (1 - 22)

There only 3 trisomies (13, 18, & 21) that result in a baby that can survive for a time after birth

The other trisomies are so devastating that the baby usually dies in utero

WARNING!

SOME OF THE PICTURES IN THE FOLLOWING SLIDES MAY BE UPSETTING/TOO GRAPHIC FOR SOME STUDENTS!

IF YOU FEEL THE NEED TO, PLEASE LOOK AWAY FROM THE SCREEN

Patau syndrome

47, XX, +13

Patau’s Trisomy Syndrome

1 in 14,000 births

47 chromosomesXY or XX

47, +13

#13 Trisomy Nondisjunction

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

Patau’s Trisomy Syndrome

Edwards Syndrome

47, XY, +18

Edward’s Trisomy Syndrome

1 in 4,400 births

47 chromosomesXX=80%

XY=20%

#18 Trisomy Nondisjunction

Edward’s Trisomy Syndrome

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

Down Syndrome47, XY, +21

1 in 1,250 births

47 chromosomesXY or XX

#21 Trisomy Nondisjunction

Down Syndrome

Down Syndrome

Short, broad hands Stubby fingersRough skinImpotency in malesMentally retardedSmall round faceProtruding tongueShort lifespan

Non-Disjunction in Sex Chromosomes

Issues arise in homologous pair 23 (X or Y)

Can be fatal

Although many people have these karyotypes and are alive and well.

Jacob’s syndrome

XYYNo abnormal

appearance/behaviorfertile

Jacob’s Syndrome

1 in 1,800 births

47 chromosomesXYY only

47XYY

#23 Trisomy Nondisjunction

Jacob’s Syndrome

Normal physicallyNormal mentally (average IQ)May have learning disabilitiesIncrease in testosteronePerhaps more aggressiveNormal lifespan

Klinefelter’s Syndrome

XXY

Found in males

Klinefelter’s Syndrome

1 in 1,100 births

47 chromosomesXXY only

47, XXY

#23 Trisomy Nondisjunction

Klinefelter’s SyndromeScarce beard

Longer fingers and armsSterileDelicate skinLow mental abilityNormal lifespanLower than average testosterone production

Turners Syndrome

45, XThe only

viable monosomy in humans

Turners Syndrome

96-98% do not survive to birthNo menstruationNo breast developmentNo hipsBroad shoulders and neck

Trisomy 16, monosomy X

46, X, +16Not viable beyond 1st

trimester

Trisomy X47 XXX symptoms

1/1000healthy and fertile -

cannot be distinguished from normal female except by karyotype

Triple X Syndrome

1 in 2,500 births

47 chromosomesXXX only

#23 TrisomyNondisjunction

Triple X Syndrome

Normally physically

Normal mentallyFertile

Cri-du-chat Syndrome

5p- site

Moon-shaped faceHeart diseaseMentally retardedMalformed larynx (have a cat like cry)Normal lifespan