advanced biology chapter 13 genetic disorders. autosomes – 22 perfectly matched chromosomes. #s...
DESCRIPTION
Sex Chromosomes – 23 rd pair XX = Female XY = MaleTRANSCRIPT
• Trisomic – Extra chromosome• 13, 15, 18 can have an extra
and survive for a short time• 21, 22 can survive into
adulthood
• Failure to separate is correlated to age:
• >20 – 1:1700 births• 20-30 – 1:1400• 30-35 – 1:750• 35-45 – 1:16
• Y Chromsome – Possesses some active genes, contains features associated with maleness
• Contains 78 genes
NONDISJUNCTION IN SEX CHROMOMSOMES• Triple X syndrome - XXX• One functional X, two Barr
Bodies• Female is sterile but normal
in other respects
NONDISJUNCTION IN SEX CHROMOMSOMES• Klinefelter Syndrome – XXY• Sterile Male• Has many female characteristics• May have diminished mental
capacity• 1:500
NONDISJUNCTION IN SEX CHROMOMSOMES• Turner Syndrome – XO• Sterile Female• Short in stature, webbed neck• Sex organs never fully mature• Low mental abilities• 1:5,000
NONDISJUNCTION IN SEX CHROMOMSOMES• Nonviable – OY• Fails to develop• Humans cannot survive
without the genes on the X chromosome
GENETIC DISORDERS• Cystic Fibrosis• Autosomal• Occurs mainly in the white
population• 1:20 carry the allele• 1:1800 are homozygous recessive
GENETIC DISORDERS• A malfunction in a channel
protein causes a thick mucus to be produced in the lungs
• Can also affect ducts in the pancreas
• Most affected individuals die in their teens
GENETIC DISORDERS• Sickle Cell Anemia• Autosomal Recessive• Occurs more frequently in the
black pop.• 1:1600
GENETIC DISORDERS• Tay-Sachs Disease• Autosomal Recessive• 1:3600 if of Jewish decent• 1:300,000 in U.S
GENETIC DISORDERS• Affected individuals lack an enzyme that
breaks down gangliosides in the brain• These accumulate in the lysosome and
burst• Resulting in the destruction of brain
cells
GENETIC DISORDERS• High risk pregnancies• Parents who are:
–Heterozygous for a disease–OlderOR have a family history
GENETIC COUNSELING• Ultrasound – position of fetus• Amniocentesis• Withdraw fluid containing fetal
cells
GENE THERAPY• Gene Transfer Therapy• 1st done in 1990• 2 Girls had a rare blood disorder
due to a defective gene• Scientists isolated working
copies of the gene
GENE THERAPY• Introduced them into bone marrow
cells taken from each girl• Gene modified bone marrow cells
were allowed to proliferate (make more)
• Injected back into body• Both girls healthy
GENE THERAPY• Use of vectors (1995)• Attach gene to a virus –
adenovirus (cold)• Like a piggyback ride• Tried it with mice and the cf
gene
GENE THERAPY• Worked, tried it with humans• Worked for awhile, but
eventually immune system attacked virus
• Caused the loss of the good gene
GENE THERAPY• Problems with the vector:
–Adenovirus elicits a strong immune response (everyone has had a cold)
–Adenovirus can produced a severe immune reaction and be fatal
GENE THERAPYProblems with the vector:–Adenovirus inserts its DNA
into cell at a random location causing mutations
GENE THERAPY• Few years later, found new
vector• Use Parovirus called Adeno-
Associated Virus (AAV)• Has only two genes and needs
the adenovirus to replicate
GENE THERAPY• Scientists removed the two
genes and insert human genes in their place to take them into the cell
• Does not cause the problems that the adenovirus did
GENE THERAPY• In 1999, AAV cured anemia in
rhesus monkeys.• Also cured dogs of retinal
degeneration• In 2000 first human trial