Advanced Biology Chapter 13 Genetic Disorders

Autosomes – 22 perfectly matched chromosomes. #s 1-22

Sex Chromosomes – 23 rd 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 21 st chromosome

Primary Nondisjunction – Failure of chromosomes to separate during Meiosis

Failure to separate is correlated to age: >20 – 1:1700 births – 1: – 1: – 1:16

Barr Body – One of the X chromosomes is inactivated

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

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

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

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

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

GENETIC COUNSELING Chorionic Villi Sampling Take a sample of placental tissue

GENE THERAPY Gene Transfer Therapy 1 st done in 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 THERAPY Problems 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