Human Heredity and Single Gene Disorders

Autosomal?

These types of gene disorders are only found in chromosome pairs 1-22

Gene Mutations

The instructions in 1 out of the 24,000 genes gets messed up

Gene MutationsInsertion, deletion or substitution of 1 or more

bases changes amino acids and makes the protein incorrectly

“Normal” DNA sequence Mutated DNA sequence

DNA: TCACGATTTmRNA: AGUGCUAAA

Ser Ala Lys

DNA: TCATGATTTmRNA: AGUACUAAA

Ser Thr

Lys

Example: Cystic fibrosis (1 in 2000 Europeans) Gene on chromosome 7

Normal dominant allele (N) makes a protein to transport chloride ions across cells

Mutated recessive allele (n) makes a protein that does not transport chloride ions across cell

Result= mucus that clogs lungs and pancreas=shortened life expectance to early adulthood

NN=normal Nn=normal nn=cystic fibrosis

Example: Tay-Sachs disease (1 in 600 Jews) Gene on chromosome 15

Normal dominant allele (N) makes a protein that is an enzyme which breaks stuff down in lysosome’s

Mutated recessive allele (n) makes an enzyme that does not work

Result= build up of waste causes nerve cells to die= brain damage and death in early childhood

NN=normal Nn=normal nn=Tay-Sachs

Example: Sickle cell anemia (1 in 500 African Americans)

Gene on chromosome 11Normal dominant allele (N) makes a protein

that carries oxygen in red blood cellsMutated recessive allele (n) makes a protein

that causes the cell to change shapeResult= Cylinder shaped red blood cells clog

blood vessels= damaged organs due to lack of oxygen

NN=normal Nn=Normal nn= sickle cell anemia

Example: Huntington’s Disease (1 in 10,000) Gene on chromosome 4

Normal recessive allele (n) makes a protein that helps move vesicles in nerve cells

Mutated dominant allele (N) makes a damaged protein which causes defected nerves in brain

Result=at middle age loss of body function and death

NN=Huntington’s disease Nn=Huntington’s disease nn= normal

Example: Hutchinson Giford Progeria Syndrome (1 in 4-8 million new borns)

Gene on chromosome 1Normal recessive allele (n) makes a protein that

builds the nucleus (nuclear envelope)Mutated dominant allele (N) makes a damaged

protein that makes the nucleus unstable and misshapen

Result=The unstable nucleus becomes damaged over time, leading to early death of cells and early death of the individual

NN=Hutchinson Gilford diseaase Nn=Hutchinson Gilford diseasenn= normal