Human Genetic Disorders

Genetic Disorder

• An abnormal condition that a person inherits through genes or chromosomes.

• Caused by mutations, or changes in a person’s DNA– May occur during meiosis or may also

have been already present in the parent’s cells

Chromosome # 7

CFTR gene

The most common allele that causes cystic fibrosis is missing 3 DNA bases. As a result, the amino acid phenylalanine is missing from the CFTR protein.

Normal CFTR is a chloride ion channel in cell membranes. Abnormal CFTR cannot be transported to the cell membrane.

The cells in the person’s airways are unable to transport chloride ions. As a result, the airways become clogged with a thick mucus.

Cystic Fibrosis

Cystic Fibrosis Prognosis

• Not sex-linked

• No cure

• Drugs to prevent infection

• Physical therapy to break up mucus in lungs

Sickle-Cell Anemia

•Genetic disorder that causes the production of abnormal hemoglobin.•Hemoglobin is a protein in RBCs that carriers oxygen.•Sickle-shape often blocks blood vessels resulting in lack of oxygen.

Genetics Behind Sickle-Cell

• 9% of African Americans carry the sickle-cell allele

• Sickle-cell allele is codominant with normal allele– Leads to resistance to malaria

• 2 Sickle-cell alleles results in sickle-cell symptoms

Hemophilia

• Genetic disorder in which a person’s blood clots very slowly or not at all.

• Individuals can bleed to death from a minor cut or scrape.

• Caused by recessive allele on the X chromosome.

Treatment• Receive doses of missing clotting

protein• Can lead relatively normal lives

Down Syndrome

•Every cell has an extra copy of chromosome 21.•Result of error during meiosis•Distinctive physical appearance and some degree of mental retardation•Many lead full, active lives.

Tools in Diagnosing Genetic Disorders

• Amniocentesis– Very long needle used to remove small

amount of fluid that surrounds the baby– Fluid contains cells from the baby

• Karyotype– Picture of all the chromosomes in a cell– Can reveal whether a developing baby

has the correct number of chromosomes in its cells and whether it is a boy or girl.

Genetic Counseling

• Helps couples understand their changes of having a child with a particular genetic disorder.

• Uses karyotypes, pedigree charts, and Punnett squares to determine if parents are carriers, etc.

Summary Questions

• Explain how genetic disorders occur in humans. Give two examples of genetic disorders.

• Describe two tools that doctors use to detect genetic disorders.

• How do the cells of people with Down syndrome differ from those of others? How might this difference arise?

Summary Questions

• A couple with a family history of hemophilia is about to have a baby girl. – What information about the parents

would you want to know? – How would this information help you

determine whether the baby will have hemophilia?