Chromosomal Disorders
Amniocentesis
Single Chromosome Single Chromosome DisordersDisorders
1. Deletion• Genetic material is
missing
2. Duplication• Genetic material is
present twice
3. Inversion• Genetic material is
“flipped”
Translocation (involves 2 Translocation (involves 2 chromosomes)chromosomes)
Translocation• Genetic material is added or swapped
from another chromosome
Chromosomal Non-disjunction• when cells go through meiosis, the chromosomes don’t
separate correctly and either too many or not enough are passed on.
What is Trisomy?• Any extra chromosome • Happens during non-disjunction!
• The non-disjunction rate increases with Mom’s age • Incidence:
– 1/750 live births. – Mothers in their early twenties have a risk of
1/1,500. – Women over 35 have a risk factor of 1/70, which
jumps to 1/25 for women 45 and over.
An Example of Trisomy
• Down’s Syndrome– A.k.a- trisomy 21– Shorthand:
• 47, XY or XX, +21– Survival rate is very
high for this non-disjunction!
Short stature, broad hands, stubby fingers and toes, a wide rounded face, a large protruding tongue that makes speech difficult. Individuals with this syndrome have a high incidence of respiratory infections, heart defects, and leukemia.
Edward’s Syndrome• This karyotype demonstrates trisomy 18
• Shorthand: (47, XY, +18).
- Incidence is only 1 in 8000 live births.
- It is uncommon for fetuses with this condition to survive
Patau’s Trisomy Syndrome1 in 14,000 births
47 chromosomesXY or XX
#13 Trisomy Nondisjunction
Small head
Small or missing eyes
Heart defects
Extra fingers
Abnormal genitalia
Mentally retarded
Cleft palate
Most die a few weeks after birth
Klinefelter Syndrome1 in 1,100 births
47 chromosomesXXY only
#23 Trisomy Nondisjunction
Scarce beard
Male anatomy
Sterile
Delicate skin
Low mental ability
Normal lifespan
Monosomy
Monosomy- having one fewer chromosome in each body cell.
Generally, if a chromosomal mutations occurs during meiosis, one half of the gametes will have monosomy and the other half will have trisomy
Turners Syndrome1 in 5,000 births
45 chromosomes X only
#23 MonosomyNondisjunction
96-98% do not survive to birthNo menstruationNo breast developmentNarrow hipsBroad shoulders and neck
Cri-Du-Chat Syndrome• 1 in 216,000 births
• 46 chromosomes
• #5 Deletion of lower arm
Symptoms:
Moon-shaped face
Heart disease
Mentally retarded
Malformed larynx
Normal lifespan