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

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

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.

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

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