G5

Question 1

What might cause deviation from mendallion ratios

Answer 1

environmental effects

genetic effects such as intralocus gene action, incomplete dominance, co dominance, interlocus gene action etc.

Question 2

what is penetrance?

Answer 2

100% penetrance = gene expressed all the time

50% penetrance = gene expressed half the time

Question 3

what is expresivity?

Answer 3

degree of expression

- colour scale etc

Question 4

give an example of a environmentally conditional mutation

Answer 4

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

Question 5

give two examples of sex limited traits

Answer 5

1. 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.
2. male mammals carry gene for milk production but dont produce milk

Question 6

what are maternal gene effects?

Answer 6

when phenotype reflects mothers genotype, not her phenotype

Question 7

give an example of maternal effect gene

Answer 7

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

Question 8

Give two examples of age onset genetic disorders

Answer 8

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

Question 9

What is genetic anticipation?

Answer 9

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

Question 10

Give examples of 4 trinucleotide repeat diseases

Answer 10

Fragile X syndrome
Huntingtons diseases
Myotonic dystrophy
Freidreich alaxaria

Question 11

what can affect imprinting epigentics?

Answer 11

maternal diet during pregnancy

Question 12

give an example of epigenetics

Answer 12

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

Question 13

When is a gene said to be epistatic?

Answer 13

when it masks the expresion of another gene

Question 14

when is a gene said to be hypostatic?

Answer 14

when a genes expression is masked by a non alllelic gene

Question 15

Give an example of epistatic control?

Answer 15

flower colour in plants
WW= White
W+W = Pink
W+M+ = blue
= 9:4:3
W = epistatic  
M = hypostatic

Question 16

Give an example of a gene modifying another gene

Answer 16

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

Question 17

Give an example of modifiers enchancing or suppressing a mutant allele of another gene

Answer 17

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

Question 18

How many mutations cause CF, what is the main one in caucasions

Answer 18

1800

F508 = 70%

Question 19

what affect does CF mutation have

Answer 19

ionic imbalance across membrane lead to secretion of more viscous fluids that obstuct lumen space = recurrent inflamation

Question 20

what are the key disease sites of CF

Answer 20

pancrea, intestine, sweat glands, male reprod tract,

Question 21

how is the CFTR pleiotropic?

Answer 21

many seemingly unrelated phenotypic effects

Question 22

what can od dieases is CF

Answer 22

autosomal recessive disorder

Question 23

What happens to patient as a result of CF

Answer 23

airway infection and inflammation
pancreatic disorders
fibrosi fatty infiltration = malabsorption; intestinal obstruction due to abnormal meconium in neonates (first poo)

Question 24

what are some potentially benefical side efffects of CF

Answer 24

increased resistance to cholera, and other infections

Question 25

what are some potentially benefical effets of huntingtons disease

Answer 25

increases fertility

reduces risk of cancer

Question 26

What is CF phenotype a mix of

Answer 26

mutations in CFTR and modifers such as envrionment - diabetes, lung ftion, weight, etc.

Question 27

is CF a monogenic disorder?

Answer 27

no thought of as oligo genic

Question 28

what affect do genotype at other loci and environment have on Duchenne dystrophy and Tay Sachs

Answer 28

very low effect of both

Question 29

what affect do genotype at other loci and environment have on sickle cell anemia

Answer 29

genotype at other loci larger effect than environment, but environment still effect

Question 30

what affect do genotype at other loci and environment have on CF

Answer 30

both ahve effect but not large

Question 31

What do studies on monogenic traits show and effects of envrionmen and role of genotype at other loci

Answer 31

that they are really oligo geneic