Lecture 5 Flashcards
(25 cards)
What kind of pea plants did Mendel pick for his experiments?
Seeds needed to either show complete recessiveness or dominance (green or yellow and smooth or wrinkled)
What are the loss of function mutations?
Amorphic (null) and Hypomorphic (leaky)
Both are usually recessive
What is the Amorphic mutation?
A loss of function mutation
No protein is produced or the produced protein doesn’t function properly, usually recessive and due to problems in the promoter region which either prevent transcription or change the amino acid sequence
What is an example of the amorphic mutation?
The CFTR protein mutation
ΔF508 CFTR gene is missing amino acid 508 which makes it unstable and so it unfolds and doesn’t exit the rER
It is degraded by proteases and so is not delivered to the chloride ion channels which prevent Cl- exiting the cell and into the mucus so mucus remains thick
What is the Hypomorphic (leaky) mutation?
A type of loss of function mutation
Protein function is reduced as less protein is made or protein is made at normal levels but the activity of it is low
What are the gain of function mutations?
Hypermorphic, Antimorphic (dominant negative), Dominant lethal and Neomorphic
What is Hypermorphic mutation?
A gain of function mutation
An increase in activity of protein; more of the protein is made or the activity of the protein increase (usually dominant)
What is an example of the hypermorphic mutation?
Trypsin-1, if it becomes activated too early, it can digest the pancreas
To avoid this, it cleaves part of itself off at arginine117 but in this mutation Arg117 is mutated to His117 which cannot be cleaved off , leading to acute pancreatitis
What is the Antimorphic (dominant negative) mutation?
A gain of function mutation
Sometimes, proteins work in complexes but if one is defect, this can affect the entire protein
What is an example of the antimorphic mutation?
A mutation in FBN1, leads to very long and thin digits
What is the Dominant lethal mutation?
Caused by an accumulation of the mutant product
What is an example of the dominant lethal mutation?
Huntington’s disease, if there are >36 CAG codons in the HD locus, this leads to the aggregation of the protein, this accumulates in the neurones and causes them to die
HD protein is transcribed slowly so this is a slow process
What is neomorphic mutation?
A gain of function mutation
Alters the function of a protein so much it causes something ‘new’ to occur
Usually dominant
What is an example of a neomorphic mutation
Drosophila, gene mutation so that legs are present where eyes should be
What is incomplete/partial dominance?
Results in a blend of characteristics
What are examples in genetics that drift from Mendelian genetics?
Incomplete/Partial dominance
Co-dominance
This is because the expression of traits is rare in nature
What is incomplete dominance?
Results in a ‘blend’ of characteristics
What is co-dominance?
The presence of both alleles is detected equally (eg: in blood)
What is recessive lethal?
A genotype does not appear in nature as it is considered ‘lethal’
What is the example that proves recessive lethal alleles?
Darker coloured mice and ‘yellow’ mice were bred to see what progeny they produced, darker mice had AA and yellow had A(y)A
The expected result was 3 yellow mice (A(y)A, A(y)A and A(y)A(y)) and 1 darker mouse (AA), using Mendel’s ratio, giving us a ratio of 3:1 but whenever this experiment was done, there was no mouse present with the A(y)A(y) genotype, indicating that this genotype is lethal
This means that in respect to colour, the yellow allele is dominant but in respect to viability, the yellow allele is considered ‘recessive lethal’
What does Matrilineal mean?
Genes only inherited from the mother
What is incomplete penetrance?
The phenotype associated with the genotype isn’t exhibited
What is variable expressivity?
Refers to the magnitude of the phenotype displayed, can be controlled by the genotype at the loci and environment
How is mitochondrial and plastid DNA inherited?
Maternally
