Transcript Karyotype

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.
Pedigree charts
• 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.
More CF
• 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.
• Boomer Esiason
Foundation
Albinism
•
Lack of pigment in
skin, hair, and
eyes.
• Approx. 1 in 17,000
people
• Dangers:
1. Eye problems
2. Severe sensitivity
to sunburn.
Autosomal dominant disorders
• These disorders
are 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
Huntingtons
• Results in a loss of muscle control and
mental function.
The symptoms usually do not appear
until after 30 years old.
• Approximately 1 in 10,000 births in
Europe and N. America
• Gene on chromosome 4
Sickle cell disease (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 the X
chromosome. Why?
• Much larger.
Color blindness gene
• Recessive gene located on the X
chromosome.
• Does color blindness affect more men
or women?
• Ans: MEN
• 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.
More hemophilia:
• Main type: hemophilia a. Body cannot
manufacture a specific protein needed
for proper blood clotting.
• Traditionally treatment: periodic blood
transfusions
• Known as the “royal disease”
• Why?
ALD (adrenoleukodystrophy)
• Similar to multiple sclerosis.
• Body is unable to break down long
chain fatty acids.
• Results in destruction of myelin
(insulating material around the nerves)
• Affects only boys. Fatal
• Depicted in the movie “Lorenzo’s Oil”
Duchenne muscular dystrophy
• Weakening and loss of muscle
tissue.
• 1 out of 3000 males born in U.S.
• Genetic disorder website
Chromosomal disorders
• A disorder resulting from either the loss
of or gain of part or a whole
chromosome.
• Nondisjuntcion : most common
chromosomal mutation.
• When a gamete contains either an extra
or one less chromosome.
• Occurs during meiosis.
Nondisjunction diagram:
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)
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