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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