Inherited Genetic Disorders & Pedigrees Unit: Genetics

Human Genetic Disorders Most genetic disorders have no cure, yet. Scientists are working on the technology that will repair/fix the “bad” genes in an organism using GENE THERAPY. Genetic Counseling: Helps parents at risk of having children with a genetic disorder. Helps them understand the options and the needs that the child would have

Genetic Disorders/Mutations Cystic Fibrosis Sickle Cell Anemia Hemophilia Phenylketonuria Tay-Sachs disease Huntington’s disease

1. CYSTIC FIBROSIS

Caused by a recessive gene on chromosome #7. Fatal Caused by a recessive gene on chromosome #7. Fatal. With the current technology people with CF can live into mid 30s Body secretions are abnormal—mucus is thick and sticky. Mucus fills lungs  difficult breathing. Same thing with digestive and reproductive systems. 1 out of 20 caucasions carry the gene. CF occurs in 1 in 2000 births. We can test for carriers.

2. Sickle Cell Anemia

- Caused by codominant alleles on chromosome #11 - HbAHbA=normal RBC, HbAHbS=both cells; HbSHbS=sickle RBC - RBCs are sickle shaped, carry less oxygen and clog blood vessels. Tissues and organs don’t get oxygen and are damaged. People with sickle cell anemia tend to be pale, tire easily, short of breath. - More common in African populations. Affects about 1 in 600 African Americans. - A test called hemoglobin electrophoresis, which causes the sickle shaped RBCs to separate from regular RBCs in a blood sample, can identify people that carry the sickle cell trait

3. Hemophilia

Caused by recessive gene on X chromosome = Sex-linked “Bleeders” disease: individuals don’t have the blood clotting protein. Need frequent transfusions or clotting factor produced by transgenic bacteria. Clotting factor needs to be used under medical supervision (too much and the bloods thickens excessively)

4. Phenylketonuria

Caused by a recessive gene. People are missing an enzyme that converts the amino acid phenylalanine into tyrosine. The build up of phenylalanine affects the nervous system and results in mental retardation. Children look normal at birth but become mentally disabled by age 1. A test can be done at birth. If positive, the child is put on a phenylalanine free diet. Phenylketonurics warning in foods! (most “sugar-free” foods) Occurs in 1 out of 14000 births.

Phenylketonuria testing at birth

5. Tay-Sachs Disease 5 years old

Caused by a recessive gene. Affects people of Jewish descent. Almost 1 out of 25 Ashkenazi Jewish people carry the Tay Sachs gene. People with Tay-Sachs lack a chemical needed to break down fatty acids deposits. Lipids accumulate in the brain and cause mental disability, blindness, early death. Test can be done at birth (blood) or during pregnancy (Amniocentesis, Chorionic Villus Sampling)

6. Huntington’s Disease

Caused by a dominant gene Symptoms appear during middle age (30-40’s) after most individuals have reproduced. Nerve cells die earlier than usual and cause mental deterioration and uncontrollable movements. Fatal.

Pedigrees A pedigree is a chart that shows the RELATIONSHIPS WITHIN A FAMILY. Helps us to understand how traits are PASSED on from generation to generation. Genetic Counselors – ANALYZE pedigree charts to infer the genotypes of family members.

A horizontal line connecting a male and female represents a marriage. A square represents a male A circle represents a female A vertical line and a bracket connect the parents to their children A half-shaded circle or square indicates that a person is a carrier of the trait. (Not always shown.) A circle or square that is not shaded indicates that a person neither expresses the trait nor is a carrier of the trait. (Not always known who is a carrier.) A completely shaded circle or square indicates that a person expresses the trait.