Basic Patterns of Human Inheritance Section 11.1 Page 296

Recessive Genetic Disorders Mendel’s work was ignored for more than 30 years. After the 1900s scientists began to take an interest in heredity and Mendel’s work was rediscovered. Dr. Archibald Garrod became interested in a disorder linked to an enzyme deficiency called alkaptonuria, which results in black urine

Dr. Garrod observed that the condition appeared at birth and then continued throughout the patient’s life The disorder also affected bones and joints He also noted that alkaptonuria ran in family and it was later determined that is was a recessive genetic disorder.

The recessive trait is expressed when the individual is homozygous recessive for that trait. ▫Round eyes  rr ▫Short pea plants  tt An individual who is heterozygous for a recessive disorder is called a carrier. ▫Carrier of cystic fibrosis  Cc

Cystic Fibrosis (CF) Affects the mucus-producing glands, digestive enzymes, and sweat glands. Patients with CF are at higher risk of infection because of excess mucus in their lungs Treatment includes physical therapy, medication, and special diets.

Albinism Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes. ▫White hair ▫Pale skin ▫Pink pupils Albinism is found in other animals as well. Absences of pigment in the eyes can cause vision problems and protection from the sun in a must

Tay-Sachs Disease (TSD) Genetic disorder found on chromosome 15 Often identified by a cherry-red spot on the back of the eye Caused by the absence of the enzyme responsible for breaking down fatty acids called gangliosides, normally gangliosides are made and then dissolved as the brain develops

Person affected by TSD, the gangliosides accumulate in the brain inflating brain nerve cells and causing mental deterioration

Galactosemia Inability of the body to digest galactose The body breaks down milk into galactose and glucose Galactose must be broken down into glucose by an enzyme named GLAT. Persons with galactosemia should avoid milk products

Dominant Genetic Disorders Those who do not have the disorder are homozygous recessive for the trait.

Huntington’s Disease Affects the nervous system (1/10,000 people in the US) Symptoms appear to affected individuals between Gradual loss of brain function, uncontrollable movements, emotional disturbances No treatment or cure

Achondroplasia Small body size and limbs Most common form of dwarfism Height 4 foot Normal life expectancy 75% of individuals with achondroplasia are born to parents of average size  the conclusion is that the condition occurred because of a new mutation or a genetic change