1. NOTES 24 – Genetic Disorders and Hereditary Diseases

2. What is a genetic disorder?
A genetic disorder is a condition caused by any abnormality in a person’s genes or chromosomes
Genetic disorders have 2 main causes

3. Cause #1
An error during meiosis causes a sperm cell or an egg cell to have some defect.
If one of these gametes is involved in fertilization, it usually results in miscarriage, but in a few cases, a baby will develop and be carried to term with a genetic disorder
EX. Down Syndrome is caused by an extra 21st chromosome in the sperm or egg cell

5. Cause #2
A defective gene present in one or both of the parents is inherited directly by the child causing a disorder
These kinds of disorders are calle hereditary diseases and follow the same rules of inheritance as other human traits

6. Hereditary Diseases Caused by Dominant Genes
Only one copy of the gene (from either parent) is needed for a person to have the disease
A person with a dominant hereditary disease usually has at least one affected parent
Parents have a 50% chance of passing these types of diseases to children

7. Ex. Huntington’s Disease
Caused by the inheritance of a dominant gene
Affects the nervous system
Produces incorrect protein that eventually leads to destruction of brain cells
Symptom’s include abnormal body movements, lack of coordination, impaired mental abilities and altered personality
Patients generally live 15 to 20 years after the appearance of the first symptoms
Currently no cure

9. Hereditary Diseases Caused by Recessive Genes
Two copies of the defective gene must be inherited (one from each parent)
Affected persons usually have two non-affected parents who are carriers
Two carrier parents have a 25% chance of having a child with the disease

10. Ex. Sickle-Cell Anemia
Caused by the inheritance of two recessive genes
Causes red blood cells to be abnormally shaped
Cells may stick to each other or become stuck in blood vessels preventing oxygen flow which may lead to organ damage or stroke
Individuals are often well, but experience painful, possibly fatal attacks from time to time

11. Sickle Cell Anemia

13. Hereditary Disease Caused by Sex-Linked Recessive Genes
Caused by defective genes carried on the X chromosome
Males affected more than women
Males inherit one defective gene on X from mother to have disorder
Females only affected if they inherit 2 defective genes (one from each parent)

14. Ex. Hemophilia
Caused by the inheritance of one recessive gene on the X (males) or two recessive genes on both X’s (females)
Affects blood – blood does not clot
Leads to severely increased risk of bleeding from common injuries
Potentially fatal

15. Hemophilia