Chpt. 11.1Basic Patterns of

Human Inheritance

PedigreesPedigree – a diagram

that traces the inheritance of a particular trait through several generations.

Carrier – heterozygous individual. They carry the trait but don't express the trait.

Reading a Pedigree

Inheritance of Human Traits

Dominant Genetic Disorders

Dominant Genetic Disorders

Caused by DOMINANT allelesSuch as RR or Rr

Huntington’s DiseaseRare but lethal genetic disorder (1/10,000)Onset between 30-50 years of ageCaused by a rare autosomal (not sex

chromosome) dominant alleleLethal disorder – a disease that causes death in

most of the individuals who are affectedThe nervous system undergoes progressive

degeneration, resulting in uncontrolled, jerky movements of the head and limbs and mental deterioration

No cure or treatment

Pedigree for Huntington’s Disease

Achondroplasia

Affects bone growth of individuals (1/25,000)Causes small body size and limbs that are short

with large head.Most common form of dwarfismAdult height of 4 feet with normal life

expectancy.No cure or treatment

Recessive Genetic Disorders

Cystic Fibrosis

• The most common lethal genetic disorder among white Americans (1/3,500)

• 1 in 20 white Americans is a carrier• 1 in 2000 children born to white Americans inherits

the disorder• Kills about 500 children/young adults each year

• Affects the mucus-producing glands, digestive enzymes, and sweat glands

• Chloride ions are not absorbed into the cells but are excreted in the sweat. Without sufficient chloride ions in the cells, a thick mucus is secreted.

Cystic Fibrosis Symptoms

Mucus in lungs & digestive tract is thick Breathing is difficult Lung infections are frequent Mucus slows secretion of some digestive

enzymes, prevents proper digestion Physical therapy, special diets, & new

drugs have raised the average life expectancy

No cure

Albinism

• Caused by altered genes, resulting in the absence of the skin pigment melanin in hair and eyes

-White hair

-Very pale skin

-Pink pupils

• Occurs 1 in 17,000

• No cure

Tay-Sachs Disease• Caused by the absence of the enzymes

responsible for breaking down fatty acids called gangliosides

• Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

• Identified by cherry-red spot in back of the eye.• Found on chromosome 15• Affects people of Jewish descent (1/2,500)• Death by age 5• No cure or treatment

Galactosemia• Characterized by the inability of the body to

digest galactose. • Lactose (from milk) breaks down into

galactose and glucose. Galactose is broken down by the enzyme GALT. People with galactosemia lack or have a defective GALT.

• Will result in mental disabilities, enlarged liver and kidney failure.

• Occurs in 1/50,000-70,000• No cure but must restrict lactose/galactose I

diet.