1. Genetic Diseases Autosomal Recessive Diseases
PKU (phenylketonuria) caused by a recessive allele found on Chromosome 12
Causes accumulation of phenylalanine in brain tissue causing mental retardation
Early identification leads to modification of dietary intake
Part of the newborn screening program
Tay-Sachs
Degenerative nervous tissue disease leading to death in the first year of life
Genetic Diseases

2. Genetic Diseases Autosomal Dominant Diseases Achondroplasia (dwarfism)
Caused by a missense mutation
Most cases are caused by a new mutation
Huntington disease… nervous tissue disease
Causes loss of muscle control eventually leading to death in their late 30s
Not part of the prenatal testing

3. Genetic Diseases Codominant Diseases Sickle cell diseases
Caused by a single nucleotide substitution in the DNA
Causes the red blood cells to form a crescent shape (sickle) when oxygen levels are low
Gives protection against malaria in the heterozygous state
The carrier is largely unaffected when healthy
Cystic fibrosis
Most commonly caused by a missing codon in the gene sequence causing the conformation of the protein to be affected.
Affected individuals have trouble moving chloride through the cell membranes causing thick pulmonary secretions and digestive problems
Very low penetrance in the heterozygous state.

4. Genetic Diseases Codominant Diseases (X-linked)
More common in males than females
Females have 1 X randomly inactivated (called a Barr body)
Colorblindness
1 in 10 males
1 in 100 females
Hemophilia… clotting disorder
Duchenne Muscular Dystrophy
Increasing loss of skeletal muscle control leading to eventual death
Genetic Diseases

5. Genetic Diseases Chromosomal disorders
Nondisjunction… failure of a chromosome to separate during Meiosis
Trisomy 21 (Down)
1 in 800 live birth
Common with increased maternal age
Turner XO
Kleinfelter’s Syndrome XXY
Both often lead to sterility