Transcript Chromosome disorders - Warren Hills Regional School District

Chromosome
disorders
Chromosome disorders are the result of
missing or extra chromosomes.
Egg and sperm cells (gametes) fuse during
Fertilization (syngamy).
Types of chromosome disorders
• Missing a chromosome =
• Monosomy – a person inherits only one
chromosome of a homologous pair
• An Extra Chromosome =
• Trisomy – a person inherits one extra
chromosome of a homologous pair
Nondisjunction:
Chromosome disorders are caused by
nondisjunction.
Nondisjunction occurs during meiosis.
Chromosomes fail to separate properly
so that gametes have abnormal
numbers of chromosomes.
Trisomy Example: Down Syndrome
The most common form of trisomy is “trisomy-21.”
An extra chromosome is inherited at autosome
pair #21. The disorder caused by trisomy 21 is
Down Syndrome.
People with Down syndrome
can lead active, happy lives.
Women who become pregnant later in life, are
more prone to have Down syndrome babies.
• Women in their 20s who become pregnant have about a one-in1,230 chance of having a pregnancy affected with Down
syndrome.
• At age 30, it's one in 690.
• By age 35, the chances increase to one in 270.
• At age 40, the risk in one in 78.
• At age 45, chances are one in 22.
They may have fetal cells screened to find out the
chromosomes present.(prenatal test)
The diagnostic picture of chromosomes
is known as a karyotype.
How do doctors get a sample of the fetal cells
to make a karyotype?
Amniocentesis – Amniotic fluid that surrounds the
fetus is drawn into a syringe. It contains some
of the fetal cells.
Living cells are removed from the
amniotic fluid. These cells are then
cultured in a medium in which
they undergo mitosis.
Amniocentesis - continued
Mitosis is stopped in metaphase using chemicals. The
cells are then placed onto a slide and spread out.
They are viewed under a microscope
which is specially adapted with a
camera to take a picture of the
chromosomes from one cell.
A magnified picture is taken of
the chromosomes.
Chromosomes on a photograph are cut out
and arranged in pairs. This is now done
with computer software.
Finished Karyotype
Other Chromosome Disorders:
People usually have two sex chromosomes.
Sometimes there can be extra or
missing sex chromosomes
• Turner’s syndrome (only one X chromosome)
X0
• Females who have Turner’s syndrome are
often mentally retarded and sterile because
their sex organs do not develop. (Some
Turners have above average intelligence.)
• Klinefelter’s syndrome Males with and extra X
chromosome. They are often mentally retarded
and sterile.
XXY
XYY Syndrome
• Boys with XYY syndrome tend to be tall and have
difficulties with language. The intelligence quotient (IQ)
tends to be slightly lower than that of other family
members. Learning disabilities, hyperactivity, attention
deficit disorder, and minor behavioral disorders can
develop.
• The XYY syndrome was once thought to cause
aggressive or violent criminal behavior, but this theory
has been disproved.
Some
Additional
Chromosome
Disorders
Patau syndrome – (Trisomy 13)
The baby may be markedly retarded. Their may be a
sloping forehead, a harelip, or a cleft palate. In
some cases microcephaly occurs. Polydactyl
hands and feet are present (extra fingers and
toes). Death may occur in hours or days from
organ defects, although some have lesser
complications and survive into young adulthood
and later (oldest living born 1982.)
Edward syndrome – (Trisomy 18)
Babies who have Edward’s
syndrome nearly always have
problems with their heart,
lungs and digestive system.
Typical characteristics
are a small head, a flat
forehead and receding
chin. Clenched fingers,
a harelip and cleft palate
may also be present. It is a
rare condition affecting about
one baby in 5,000. Death
usually occurs in 3 – 4 months.