Chapter 13 Genetic Disorders Advanced Biology Chapter 13 Genetic Disorders

Autosomes – 22 perfectly matched chromosomes.

Sex Chromosomes – 23rd pair XX = Female XY = Male

Monosomic – Lost one copy of a chromosome Usually fatal, especially if on an autosome

Trisomic – Extra chromosome 13, 15, 18 can have an extra and survive for a short time 21, 22 can survive into adulthood

Down Syndrome – Trisomy 21 Extra copy of the 21st chromosome

Primary Nondisjunction – Failure of chromosomes to separate during Meiosis

Failure to separate is correlated to age: >20 – 1:1700 births 20-30 – 1:1400 30-35 – 1:750 35-45 – 1:16

Barr Body – One of the X chromosomes is inactivated

Y Chromsome – Possesses some active genes, contains features associated with male-ness 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

NONDISJUNCTION IN SEX CHROMOMSOMES Klinefelter Syndrome – XXY Sterile Male Has many female characteristics May have diminished mental capacity 1:500 NONDISJUNCTION IN SEX CHROMOMSOMES

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

NONDISJUNCTION IN SEX CHROMOMSOMES Nonviable – OY Fails to develop Humans cannot survive without the genes on the X chromosome NONDISJUNCTION IN SEX CHROMOMSOMES

Multiple alleles – Some traits possess multiple alleles for that specific trait Blood types.

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

GENETIC DISORDERS Sickle Cell Anemia Autosomal Recessive Occurs more frequently in the black pop. 1:1600 GENETIC DISORDERS

Hemoglobin is defective; doesn’t carry enough Oxygen GENETIC DISORDERS

Phenylketonuria (PKU) Autosomal recessive 1:15,000 GENETIC DISORDERS

GENETIC DISORDERS Inability to breakdown phenylalanine (aa) Can be controlled by nutrition GENETIC DISORDERS

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

GENETIC DISORDERS Sex-linked recessive Inability of blood to clot Missing a clotting factor GENETIC DISORDERS

GENETIC DISORDERS Huntington’s Disease DOMINANT 1:10,000 Gene gets turned on in middle age GENETIC DISORDERS

Deterioration of brain cells due to the inhibition of brain cell metabolism GENETIC DISORDERS

GENETIC DISORDERS High risk pregnancies Parents who are: Heterozygous for a disease Older OR have a family history GENETIC DISORDERS

GENETIC COUNSELING Ultrasound – position of fetus Amniocentesis Withdraw fluid containing fetal cells GENETIC COUNSELING

GENETIC COUNSELING Chorionic Villi Sampling Take a sample of placental tissue GENETIC COUNSELING

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

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

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

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 THERAPY

GENE THERAPY Problems with the vector: Adenovirus inserts its DNA into cell at a random location causing mutations GENE THERAPY

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

GENE THERAPY In 1999, AAV cured anemia in rhesus monkeys. Also cured dogs of retinal degeneration In 2000 first human trial GENE THERAPY

https://www.youtube.com/watch?v=bLI1Gfb0ynw https://www.youtube.com/watch?v=5SC2EoxUOXo https://www.youtube.com/watch?v=Ez560GnkSrE