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