L5: Gene Interaction I Flashcards
Describe amorphic loss of function
Produces no protein at all, protein lacks function
- Usually recessive
Example of amorphic loss of function mutation
CFTR mutation (Δ508) in cystic fibrosis
- Prevents proper Cl- transport
- Mucus becomes thicker
- Lung infections
What is the primary role of CFTR in cells?
Regulating chloride ion and water transport
Is wild type CFTR dominant/recessive, and why?
Dominant- phenotype can mask recessive allele 1 wild-type copy is able to maintain the Cl- gradient
Is CFTR(Δ508) dominant/recessive, and why?
Recessive- CF only appears if an individual is homozygous for this allele
What type of mutation leads to cystic fibrosis when homozygous?
Recessive mutation
Describe hypomorphic (leaky) loss of function mutation
protein function is reduced due to less protein made
- usually recessive
An example of hypomorphic loss of function mutation
Alleles of gene encoding tyrosinase- produces melanin
Describe hypermorphic gain of function mutation
Increase in activity, more protein made or greater activity
- Usually dominant
Example of hypermorphic gain of function mutation
Trypsin-1 mutation from ARG117 to H117
- Leading to hereditary pancreatitis (HP)
Describe antimorphic gain of function mutation
Disturbance in function interfering with protein encoded by normal allele (wild type)
Example of antimorphic gain of function mutation
Mutations in FBN1 encoding fibrillin-1
- Unusually tall, long limbs
Describe dominant lethal gain of function mutation
Later on in life due to accumulation of the mutant product
- In order to exist in a population, affected individual must reproduce before dying
Example of dominant lethal gain of function mutation
Huntington’s disease (40yrs)
- Caused by triplet expansion in the HD locus (>36 CAG), polyglutamine tract in the protein
- Leads to aggregation of protein into neurotoxic fibrils
Describe neomorphic gain of function mutation
Causes a dominant gain of gene function that is different from normal function
Describe incomplete (partial) dominance
Results in a ‘blend’ of characteristics
e.g pink flowers from red x white crosses
Describe co-dominance
Presence of both alleles is detected equally
Describe recessive lethal alleles
Homozygous individuals die
e.g yellow coat allele in mice
Describe dominant lethal alleles
Heterozygous individuals affeceed
What does it mean for a trait to be sex-limited?
The trait’s phenotype is absolutely limited to one sex
Describe X-linked inheritance
- Males inherit X-linked traits from mother
- Affected fathers pass alelles to all daughters, NOT SONS
Example of X-linked inheritance
Haemophilia A (blood clotting factor VIII on X chromosome)
Describe sex-limited traits
Only expressed in 1 sex
e.g milk production in cattle
Describe sex-influenced traits
Expression depends on hormone levels
e.g male-pattern baldness (dominant in males, recessive in females)
Describe maternal inheritance
Mitochondria & chloroplasts contain their own DNA
- Inherited from mother
Describe incomplete penetrance
phenotype associated with genotype fails to appear
example of incomplete penetrance
polydactylyl
Describe variable expressivity
phenotype varies in severity
What is penetrance & expressivity controlled by?
i) genotype at other loci
ii) environmental factors
