Gene interaction:
Dominance and lack of dominance
I. Loss of function:
1. Amorphic (null):
No production of protein or the protein has been destroyed chemically and lost its
function; usually recessive
e.g. CFTRΔ508 allele Cystic fibrosis transmembrane conductance regulator
gene that makes the chloride channel (important in the lung)
Δ508 codon is missing ;
phenylalanine is missing
CFTR, pumps Cl- out of cells, leads to water exiting the cell by osmosis (outside the surfaces
of alveolar cells there is a layer of mucus which stays fluid)
This mucus layer catches the bacteria that we have breathed in and washes them away
=>because of that we do not get lung infection
, Mutant CFTRΔ508 does not exit the endoplasmic reticulum because an amino acid is missing
=> the protein is unstable unfolded proteins cause Parkinson
Loss of Cl- gradient, mucus becomes thicker, leads to lung infections, blockage of ducts in
pancreas and intestines
if homozygous: cystic fibrosis =>lifespan reduced (ca. 50% reach 40ys)
Wild-type CFTR is Dominant –phenotype can mask the recessive allele because one wild-
type copy is able to maintain the Cl- gradient.
CFTRΔ508 is Recessive – only if individuals are homozygous for this allele – cystic fibrosis
2. Hypomorphic (leaky):
Protein function is reduced either due to less protein made, or product itself displays less
activity; ususally recessive
e.g. alleles of the gene encoding Tyrosinase- in the pathway that produces melanin from
tyrosine
Dominance and lack of dominance
I. Loss of function:
1. Amorphic (null):
No production of protein or the protein has been destroyed chemically and lost its
function; usually recessive
e.g. CFTRΔ508 allele Cystic fibrosis transmembrane conductance regulator
gene that makes the chloride channel (important in the lung)
Δ508 codon is missing ;
phenylalanine is missing
CFTR, pumps Cl- out of cells, leads to water exiting the cell by osmosis (outside the surfaces
of alveolar cells there is a layer of mucus which stays fluid)
This mucus layer catches the bacteria that we have breathed in and washes them away
=>because of that we do not get lung infection
, Mutant CFTRΔ508 does not exit the endoplasmic reticulum because an amino acid is missing
=> the protein is unstable unfolded proteins cause Parkinson
Loss of Cl- gradient, mucus becomes thicker, leads to lung infections, blockage of ducts in
pancreas and intestines
if homozygous: cystic fibrosis =>lifespan reduced (ca. 50% reach 40ys)
Wild-type CFTR is Dominant –phenotype can mask the recessive allele because one wild-
type copy is able to maintain the Cl- gradient.
CFTRΔ508 is Recessive – only if individuals are homozygous for this allele – cystic fibrosis
2. Hypomorphic (leaky):
Protein function is reduced either due to less protein made, or product itself displays less
activity; ususally recessive
e.g. alleles of the gene encoding Tyrosinase- in the pathway that produces melanin from
tyrosine
