Mrs. Degl

Human Heredity and Genetic Disorders

•Pedigree Charts show patterns of inheritance•Pedigree Charts show that presence or absence of certain traits•Pedigree Charts make it possible to show the carriers of recessive genes.•Males are usually square and females are usually a circle

Mrs. Degl

Examples of Human Genetic Disorders

1. Sickle-cell Anemia

•This is a blood disorder found mostly in African Americans.•It is caused by a gene mutation that results in the production of abnormal shaped red blood cells.•These sickle cells cannot carry O2 efficiently, resulting in anemia, and severe pain.

Mrs. Degl

2. Tay-Sachs Disease

•A recessive genetic disease in which nerve tissue in the brain deteriorates because of an accumulation of fatty material.•The disorder is a result of the body’s inability to synthesize a particular enzyme.•It is fatal•It occurs mostly among Jewish descent.

Mrs. Degl

3. PKU (Phenylketonuria)

•A disorder in which the body cannot synthesize the enzyme necessary to metabolize (break down) the amino acid phenylalanine.•Without this enzyme, phenylalanine accumulates in the blood and body tissues. •This disease is homozygous recessive and causes severe mental retardation if not detected at birth.•If detected at birth, retardation can be prevented by maintaining a phenylalanine free diet.•Classic PKU affect about one of every 10,000 to 20,000 Caucasian or Oriental births. The incidence in African Americans is far less.

Mrs. Degl

Detecting Genetic Disorders1. Screening: Blood or urine screening can detect certain

genetic disorders like PKU, Sickle-cell Anemia, and Tay-Sachs Disease.

2. Karyotyping: A greatly enlarged photograph of chromosomes is viewed and examined to see if there are any abnormalities in number or structure.

3. Amniocentesis: A technique in which a small sample of amniotic fluid is taken from the amniotic sac of a pregnant woman. The fluid contains fetal cells which can be examined with karyotyping. Sickle-cells, Tay-Sachs Disease and Down Syndrome can be detected this way, among other abnormalities.

4. Genetic Screening: The techniques above, along with pedigree charts are used by genetic counselors, for couples with genetic disorders in their families.