G5 Flashcards
What might cause deviation from mendallion ratios
environmental effects
genetic effects such as intralocus gene action, incomplete dominance, co dominance, interlocus gene action etc.
what is penetrance?
100% penetrance = gene expressed all the time
50% penetrance = gene expressed half the time
what is expresivity?
degree of expression
- colour scale etc
give an example of a environmentally conditional mutation
coat colour in mammals
himilayan allele is temperature sensitive mutation, enzyme is function al lower temperatures leading from colourless precursor to black clour.
extremeties are colder so get colour there but not on main body.
if raise rabbits above 20 degrees = completely white
give two examples of sex limited traits
- feathering in fowls, HH/Hh is hen feathered in both cocks and hens. however hh is hen fethered in hens but cock featherd in cocks, if remove ovaries from hh hen then would be cock feathered
= not sex linked = sex limited. - male mammals carry gene for milk production but dont produce milk
what are maternal gene effects?
when phenotype reflects mothers genotype, not her phenotype
give an example of maternal effect gene
shell coiling in snail Linnaea, dextral coils right D, sinistral coils left dd. D is dominant.
however if mother is dd and mates with DD father offspring are Dd, but they are sinistral, because the mother was sinistral.
if these offspring are crossed then get dd, Dd, Dd, dd and DD all of which are dextral, because the mothers genotype was dextral
Give two examples of age onset genetic disorders
tay sachs disease: autosomal recessive, lethal lipid methbolism disease = fatal by 3. blindness, retardation adn paralysise
Huntingtons disease - autosomal dominant allele of huntingtons gene - frontal lobe of cerebral cortest, deteroration over a decase - onset 38
What is genetic anticipation?
when heritable disorders exhibit a progressively earlier age of onset and increase severity in successive generations
generally due to trinucleptode repeat = unstable and expantion related to eaerlier onset
Give examples of 4 trinucleotide repeat diseases
Fragile X syndrome
Huntingtons diseases
Myotonic dystrophy
Freidreich alaxaria
what can affect imprinting epigentics?
maternal diet during pregnancy
give an example of epigenetics
Imprinting
cross heterozygotes with one mutant and one wildtype form
mothers wildtype form in imprinted = not expressed
shown in mouse
WxWi = normal, WxM = normal MxWi = dwarf, MM = mutant
When is a gene said to be epistatic?
when it masks the expresion of another gene
when is a gene said to be hypostatic?
when a genes expression is masked by a non alllelic gene
Give an example of epistatic control?
flower colour in plants WW= White W+W = Pink W+M+ = blue = 9:4:3 W = epistatic M = hypostatic
Give an example of a gene modifying another gene
eg. quantitavely reducing expression 5 genes determine coat colour in mammals D= full colour dd= dilutes. B=black bb= brown S = even colour dist ss= spots A = agouti aa= not agouti C = colour expression cc = albino
Give an example of modifiers enchancing or suppressing a mutant allele of another gene
Intergenic suppression; heterodimer suppression
two genes produce polypetitides
both wild type = functional
one mutates = not functional
second mutation = acts as a suppressor = functions
suppressor mutation by itself = doesnt function
How many mutations cause CF, what is the main one in caucasions
1800
F508 = 70%
what affect does CF mutation have
ionic imbalance across membrane lead to secretion of more viscous fluids that obstuct lumen space = recurrent inflamation
what are the key disease sites of CF
pancrea, intestine, sweat glands, male reprod tract,
how is the CFTR pleiotropic?
many seemingly unrelated phenotypic effects
what can od dieases is CF
autosomal recessive disorder
What happens to patient as a result of CF
airway infection and inflammation
pancreatic disorders
fibrosi fatty infiltration = malabsorption; intestinal obstruction due to abnormal meconium in neonates (first poo)
what are some potentially benefical side efffects of CF
increased resistance to cholera, and other infections
what are some potentially benefical effets of huntingtons disease
increases fertility
reduces risk of cancer
What is CF phenotype a mix of
mutations in CFTR and modifers such as envrionment - diabetes, lung ftion, weight, etc.
is CF a monogenic disorder?
no thought of as oligo genic
what affect do genotype at other loci and environment have on Duchenne dystrophy and Tay Sachs
very low effect of both
what affect do genotype at other loci and environment have on sickle cell anemia
genotype at other loci larger effect than environment, but environment still effect
what affect do genotype at other loci and environment have on CF
both ahve effect but not large
What do studies on monogenic traits show and effects of envrionmen and role of genotype at other loci
that they are really oligo geneic
