Download Karyotype

The Human
Genome
Chapter 14
Human Chromosomes
• Karyotype: a picture
of the chromosomes
from a single cell.
• Used to determine
the sex, or possible
genetic disorders of
an individual.
• 44 autosomes
• 2 sex chromosomes
Determining the sex of a zygote:
• Always determined
by the father.
• All eggs contain
one X chromosome
• Sperm either
contain one X
chromosome or one
Y chromosome.
Pedigrees
• Used to show how a particular trait is
passed from one generation to the
next in a family
Blood types
• Controlled by more than one gene
• A, B, O, AB
• Rh factor
Genetic disorders
• Recessive disorders most
common
• To be afflicted with a
recessive disorder, one must
have 2 copies of each
recessive allele.
PKU (phenylketonuria)
• The body cannot break down the amino
acid phenylalanine
• Nutrasweet could be deadly
• If not detected early, or if a specific diet
is not followed, serious brain damage can
occur.
• 1 in 60 Caucasians are carriers of the
gene that causes PKU.
• The gene is found on chromosome 12
Tay-Sachs
• Cannot break down certain fats.
• Results in brain damage
• The gene is found on chromosome
15
• Mainly affects people of European
Jewish ancestry (1 in 30 are
carriers)
Cystic Fibrosis
• Affects digestive system and absorption
of fats.
• Causes a build up of mucus in the
lungs.
• CF kids are often more likely to develop
pneumonia.
• One of the first disorders to be actively
studied for gene therapy.
CF (cont.)
• Sweat test
• Gene found on
chromosome 7
• 1 in 25 people are
carriers.
• Most lethal
autosomal recessive
disorder in U.S.
• No cure
Treatment
• Respiratory therapy
• Enzyme therapy (DNAse)
• Lung transplants
Albinism
• Lack of pigment
in skin, hair, and
eyes.
• Approx. 1 in
17,000 people
• Risks:
1. Eye problems
2. Severe
sensitivity to
sunburn.
Autosomal dominant disorders
• Expressed when
the dominant
allele is present
in the
genotype.
Achondroplasia
• A form of dwarfism
• The torso is of normal size, but
arms and legs are very short.
• Average adult height of 4 feet.
• 1 in 25,000 births.
• Gene is found on chromosome 4
• “Little People”
Huntingtons
• Results in a loss of muscle control and
mental function.
• Breakdown of nerve cells in the brain
• Approximately 1 in 10,000 births in
Europe and N. America
• Gene on chromosome 4
• Symptoms after age 30
• Autosomal Dominant
Marfan Syndrome
• Mutation in the fibrilin gene that makes
proteins found in tendons/ligaments
• Results in TALL stature
• Heart problems
• Abe Lincoln
was suspected
to have M.S.
Sickle cell anemia
• Codominant disorder found in African
Americans.
• Red blood cells are misshapen.
• Characterized by extreme pain in legs
and arms because the cells get stuck in
capillaries.
• Can be fatal
• The gene can prevent Malaria
Sickle-cell cont’d
• Approx 1000 babies
born each year
• 1 in 400 African
Americans
• Possible cure: bonemarrow transplants
• Treatment:
– Avoid being overly
active
– Watch your diet
Sex-linked genes and disorders
• A situation in which an organism’s
sex can affect the chances of
inheriting a gene.
• First studied by Morgan with fruit
flies
• Most sex-linked genes are found on
the X chromosome
Color blindness gene
• Recessive gene located on
the X chromosome.
• Men only have one X
chromosome, thus only
one copy of the color blind
gene.
Color Blindness
Hemophilia
• A disorder in
which a
person’s blood
does not clot
properly.
• Gene found on
X chromosome.
• 1 in 10,000
males born are
afflicted.
Hemophilia:
• Main type: hemophilia a. Body
cannot manufacture a specific
protein needed for proper blood
clotting.
• Traditional treatment: periodic
blood transfusions
• “Bleeder’s disease”
Duchenne muscular dystrophy
• Weakening and loss of muscle
tissue.
• 1 out of 3000 males born in U.S.
• Sex-linked/recessive
• Caused by absence of dystrophin, a
protein that helps keep muscle cells
intact.
• Genetic disorder website
Chromosomal disorders
• loss of or gain of part or a
whole chromosome.
• Nondisjunction - most common
chromosomal mutation.
• When a gamete contains either
an extra or one less
chromosome.
• Occurs during meiosis.
Down Syndrome
• Also known as Trisomy 21 because of
the presence of an extra chromosome
21.
• Symptoms similar to mental retardation
• Approx 1 in 800 babies born in U.S.
• Chances of having a baby with Down
Syndrome increases with the age of the
mother.
Sex Chromosome Disorders:
• Turner’s syndrome: In females, a
person only inherits one X chromosome
(45,X)
• Klinefelter’s syndrome: In males, an
extra X chromosome is present
(47,XXY)
Hutchinson-Guilford Progeria
• One mistake in the DNA sequence
of the gene, LMNA causes
Progeria. (point mutation)
• The LMNA gene normally makes a
protein called lamin A, and helps
maintain the shape and function of
the cell.
• The mutation causes the
gene to produce an
abnormal Lamin A protein
called progerin.
• In children with Progeria,
many cells in the body
make progerin protein.
• As the children age,
progerin builds up in these
cells causing progressive
disease-Rapid aging
DNA analysis
• Testing for alleles : makes it possible to
determine if a person can pass on a
particular disorder to his or her
children.
• DNA fingerprinting
Human Genome Project
• Began in 1990.
• The goal was to analyze the entire
human DNA sequence (6 billion base
pairs)
• Originally scheduled to be completed in
2005
• In June 2003, the map was completed
Gene Therapy
• Replacing an absent or faulty gene with
a copy of a “good” or working gene.
• Still considered a radical therapy.
• Has not been tested thoroughly.
Assignment:
• Page 363-364
–1-10, 12,14,17,19,23,25,26,29