Genetic Disorders
Cystic Fibrosis
• Caused by a recessive allele
on chromosome 7
• It is inherited in a autosomal
recessive pattern.
• People with cystic fibrosis
lack one amino acid in the
CFTR gene, causing a thick
mucus that clogs the lungs.
Genetic Disorders
Ideogram: A diagram of a chromosome
• Ideograms show can show the position
of specific genes:
• The CFTR gene is located at 7q31.2
• 7th chromosome
• q = long arm of the chromosome
(p = short arm of the chromosome)
• 31.2 represents the position on the
arm (band number)
Genetic Disorders
Huntington’s Disease
• Caused by a dominant allele
• The DNA sequence – C A G – is
repeated over several times.
• This causes the Huntingin protein
to become deformed which
damages the nervous system.
• Most genetic disorders are
inherited as a recessive trait.
• Why are dominant genetic
disorders more rare than recessive
disorder?
Genetic Disorders
Why does Huntington’s disorder
get passed from generation to
generation.
• Causes gradual damage to the
nervous system resulting in loss
of muscle control and mental
function.
• People who have the disease
show no symptoms until their
thirties or forties (after they
passed the allele to their
children).
Genetic Disorders
Sickle Cell Disease
• Characterize by “sickle” shaped red
blood cells
• Caused by a mutation of the
hemoglobin gene on chromosome 11.
• People who are heterozygous for the
sickle cell trait have both normal and
sickle shaped red blood cells.
• What is the pattern of inheritance
Genetic Disorders
• Sickle Cell allele is carried by 1 in 12 of African ancestry
• Most genetic disorders are extremely rare. Why is
sickle cell so common?
• Those who are heterozygous for Sickle cell are
resistant to malaria.
• The benefits of being heterozygous outweighed the
risks the of passing on both parents passing the
allele for the disease.
Disorders Caused by Individual Genes
http://www.portal.state.pa.us/portal/server.pt?open=514&objID=558226&mode=2
PKU, or phenylketonuria
•
•
•
Caused by a recessive allele found on chromosome 12
Phenylalanine is an amino acid found in milk and other foods
People who lack the enzyme needed to break down
phenylalanine have the amino acid build up in tissues and cause
severe mental retardation.