Transcript Abnormal numbers of autosomes

Diseases and karyotypes
• Definitions
• Autosomes- any chromosome that is not
a sex chromosome. Not the “X” or “Y”
• Sex-linked- genes located on the sex
chromosome. Usually on the “X”
• Nondisjunction- A chromosome mishap
in meiosis
Abnormal numbers of
autosomes
• Metaphase chromosomes are
photographed;
• the chromosome pictures are then
enlarged and
• arranged in pairs by a computer
according to length and location of
the centromere.
Abnormal numbers of autosomes
• This chart of chromosome pairs is
called a karyotype, and it is valuable
in identifying unusual chromosome
numbers in cells.
• A Karyotype is a photograph of the
chromosomes of a single cell.
Another view
Normal
Female
Normal
Male
?
Colchicine
added to cells
Cells broken open
Picture of
chromosomes
taken
Microscope
zooms in
Chromosomes cut
up and arranged
Chromosomal Disorders
Individuals are missing a
chromosome or have an extra
chromosome
Down syndrome: Trisomy 21
• Down syndrome is
the only autosomal
trisomy in which
affected individuals
survive to
adulthood.
• It occurs in about
one in 700 live
births.
Down syndrome: Trisomy 21
• Down syndrome is a group of symptoms that
results from trisomy of chromosome 21.
• Individuals who have Down syndrome have at
least some degree of mental retardation.
• The incidence of Down syndrome births is
higher in older mothers, especially those over
40.
Chromosome 21
Abnormal numbers of sex
chromosomes
• Many abnormalities in the number of sex
chromosomes are known to exist.
• An X chromosome may be missing (designated
as XO) or there may be an extra one (XXX or
XXY). There may also be an extra Y
chromosome (XYY).
Klinefelter’s
Syndrome
XXY
• Poor beard growth
• Tend to grow fewer
chest hairs
• Breast development
• Wide hips
• Long legs
• Narrow shoulders
Karyotype of a male with
Klinefelter’s syndrome
•Short (<59”)
XO
•Webbed neck
•Sterile
•Low hairline
Karyotype of a female with Turner’s
syndrome
Autosomal Genetic Disorders
• These are a result of genes on the 22
pairs of chromosomes that are not the sex
chromosomes (not X and Y)
Sickle Cell Anemia
• Autosomal Recessive
• Affects the blood
• Symptoms: impaired blood circulation,
organ damage
• Defect: Abnormal hemoglobin molecules –
RBC’s
• 1/500 African Americans -If heterozygous
will not get malaria
Sickle-cell disease
• Abnormally shaped blood cells, slow blood flow,
block small vessels, and result in tissue
damage and pain.
Normal red
blood cell
Sickle cell
Cystic Fibrosis
• Recessive allele
• Affects the lungs and digestive tract
• Characterized by thick mucus in
lungs and digestive tract
• Food is not digested properly
• Breathing is difficult - frequent lung
infections
• .Most common lethal genetic
disorder in white Americans.
• Approximately one in 28 white
Americans carries the recessive
allele, and one in 2500 children born
to white Americans inherits the
disorder.
Cystic Fibrosis
On chromosome 7 there is a mutation in a gene
that causes a thick mucus to develop
This is a frame shift
mutation
• Autosomal dominant—carriers GET the
disease
• Affects the central nervous system
• Causes nerve death in the brain. Starts
with spasms and eventually leads to a
vegetable like state and death. Onset
between 30 and 50.
Huntington’s Disease
Huntington disease affects an estimated
3 to 7 per 100,000 people of European
ancestry. The disorder appears to be
less common in some other populations,
including people of Japanese, Chinese,
and African descent.
Defect on
Chromosomes
number 4
Typical Pedigree of Huntington’s Disease
I
1
2
II
2
1
4
3
5
III
1
2
3
4
5
Phenylketonuria (PKU)
• Autosomal recessive
• Affects: brain
• Symptoms: Failure of brain to develop
in infancy; if untreated causes death.
• Defect: Caused by absence of
enzyme that converts phenylalanine
to tyrosine (amino acids)
• 1/18,000 urine test, treated by diet until puberty.
Phenylketonuria
(PKU)
• Most common in people of
Norwegian and Swedish
descent.
Symptoms of PKU
• New born appears normal.
• Once baby starts drinking
milk, which is high in
phenylalanine, damage
occurs
Symptoms
• Build up in phenylalanine
causes severe central
nervous system damage
resulting in mental
retardation.
Treatment of PKU
• All newborns are tested for
PKU.
• Changes in diet can prevent
damage. Given a diet low in
phenylalanine until the brain
is fully developed.
Phenylketonuria
Phenylketonurics: Contains Phenylalanine
Tay-Sachs disease
• Tay-Sachs (tay saks) disease is a recessive
disorder of the central nervous system.
• In this disorder, a recessive allele results in the
absence of an enzyme that normally breaks
down a lipid produced and stored in tissues of
the central nervous system.
• Because this lipid fails to break down properly,
it accumulates in the cells.
Symptoms of
Tay-Sachs Disease
• Blindness
• Progressive loss of
movement
• Mental deterioration
• Death by age 5.
I
1
2
Typical
Pedigree
for
Tay-Sachs
II
1
2
3
4
1
2
III
3
IV
1
Sex-linked traits
• These are genes that are found on the X
chromosome. They are generally more
common in males than in females.
• Females need to have it on both their X
chromosomes ( get from mom and dad)
• Since males only have 1 X chromosome,
they only need to have received the allele
from their mother for the trait to show.
Sex-linked trait
Hemophilia
• X-linked recessive
• Defect: defective form of blood-clotting
agent.
• Symptoms: failure of blood to clot
• About one male in every 10 000 has hemophilia,
but only about one in 100 million females
inherits the same disorder.
Hemophilia: An X-linked
disorder
• Males inherit the allele for hemophilia on the X
chromosome from their carrier mothers. One
recessive allele for hemophilia will cause the
disorder in males.
• Females would need two recessive alleles to
inherit hemophilia.
• Some genetic disorders are both genetic
and environmental. People inherit the
tendency to a trait, but how and when it is
expressed depends on environmental
factors such as diet, exercise, exposure to
chemicals, etc.
Diabetes
Asthma
Cardiovascular
Disease