Chromosome
Disorders
Prenatal Diagnosis
Amniocentesis
• A small sample of the amniotic fluid
surrounding the baby is removed using a
syringe.
• The fluid contains skin cells from the baby.
• The skin cells are grown in the lab.
• The chromosomes from the cells are
magnified under a microscope and a
picture is taken.
• The chromosomes are cut out and
arranged in homologous pairs in
decreasing size order.
• This is called a karyotype.
Down Syndrome (Trisomy 21)
• Extra chromosome 21 in
every cell of the body
• Causes mental retardation, heart defects
• Karyotype = 47,XX+21 or 47,XY+21
• As a woman gets older, her chances of
having a baby with a chromosome
abnormality increases
***remember, a woman is born with all of her
egg cells, but meiosis is not yet complete
(egg development stops in prophase I until
the follicle matures prior to ovulation)
• Most cases of Down syndrome are caused
by nondisjunction during meiosis
• Nondisjunction: homologous
chromosomes do not separate properly
http://www.mhhe.com/biosci/genbio/biolink/j
_explorations/ch10expl.htm
Turner Syndrome
45,X
Characteristics
•
•
•
•
•
short stature
ovaries do not develop (infertile)
cardiovascular problems
kidney and thyroid problems
skeletal disorders such as scoliosis
Klinefelter Syndrome
47,XXY
Characteristics
• Infertility (cannot produce a lot of sperm)
• Learning disability
Trisomy 13
• severe birth
defects
• mental
retardation
Trisomy 18
• severe birth
defects
• mental
retardation