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Non- Disjunction Disorders
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
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 Syndrome1 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 Syndrome1 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 Syndrome1 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
