lecture 8 - sae 1

Question 1

describe interactions between genes in a single pathway

Answer 1

one gene one enzyme hypothesis
genes in sam pathway
assume on diff chromosomes - not a distance factor
like amino acids - things build on each other to eventually make final product

Question 2

how to identify genes involved in a biochemical pathway

Answer 2

forward genetic screens - xrays shine through organism so random gene mutations

Question 3

describe process of identifying genes involved in biochemical pathway

Answer 3

isolate each spore in the ascus and grow each separately in tubes
genotype the same since starting from same
on complete medium = has everything it needs to grow, like nutrients
on minimal medium = basically carbs - sugar molecules, lacks vitamins and aas = MUTANT WONT BE ABLE TO GROW = since cannot synthesize certain metabolites

Question 4

what happens if cannot grow on minimal medium

Answer 4

identifies nutritional mutant
start adding back stuff that mutant could need
= discovers its aas missing
then test on medium - each different aa, when arginine supplemented = will grow, so mutant cannot produce arginine from basic metabolites

Question 5

describe interactions between genes in pathways - ex

Answer 5

difference mutants on enzymes = can affect pathway of making an amino acid
arg 1 = can growth as long as ornithine
arg 2 = can grow as long on citrulline
arg 3 = cannot grow with precursors need arginine directly
if mutation on something upstream = downstream pathway intact

Question 6

describe what forward genetic screening tells us

Answer 6

mutants carrying mutations in diff genes can be isolated - arg1, arg2, arg3
multiple mutant alleles of the same gene can also be isolated - diff mutant alleles carrying mutations in arg1

Question 7

what must we first determine when studying gene interactions

Answer 7

determine whether mutations are alleles of the same gene or diff genes
loss of function mutations = affected by mutation of same gene

Question 8

what is complementation test

Answer 8

can be used for recessive mutations
to figure out if on same gene

Question 9

describe is 2 diff genes - complementation test

Answer 9

if appears wild type
must create heterozygous
chances more likely that it carries wild type
chance it being mutated = low
no longer see deficiency since each gene complemented by wild type of other gene

Question 10

describe if 2 alleles on same gene - complementation test

Answer 10

homozygous
for mutants = cross with another mutant
appears mutant
since failed to complement = must mean it on same gene

Question 11

describe complementation testing - white flowered mutants

Answer 11

white recessive to blue
F1 monohybrid cross will tell if phenotype is caused by on gene or multiple genes = 3:1 ratio of blue to white - if deviated = can assume mutation caused by more than one gene
do complementation test - if failed to complement= must have mutation on same gene

Question 12

what does genetic interaction result in

Answer 12

modified 9:3:3:1 ratio
phenotypically

Question 13

describe how ratio can be changed - genetic interaction

Answer 13

2 enzymes make flowers blue - double mutant = acts as only have single mutant
- same if acting on same pathway
9:7 ratio = 2 genes in same pathway
same linear pathway - most of time

Question 14

describe interaction between regulator gene and target gene

Answer 14

target gene depends on transcription factor (expression of A completely depends on transcription factor coded by R)
NORMAL = 9
NO protein produced = when mutation in gene that encodes regulatory protein and when mutation in both genes
mutant protein = when mutation in gene that encodes structural protein
THESE 3 all produce non functional = 7
if 9:7 ratio = assume act on same pathway, have regulatory relationship to each other

Question 15

describe mendelian ratio of 2 genes affecting the same characteristic but work independently

Answer 15

act on same biological process but diff pathway
2 genes control snake colour = O (orange) and B (black)
O+B = camouflage
= typical ratio 9:3:3:1 (camo, black, orange, albino)
have nothing to do with each other functionally, double mutant diff than single mutant

Question 16

what is epistasis

Answer 16

a situation where phenotypic manifestation of an allele is dependent on the genotype of a different gene
does not have to be on same pathway but can be

Question 17

what is recessive epistatic - example, formal

Answer 17

recessive genotype of one gene - w - masks pink flower phenotype associated with other gene - m -
w is epistatic to m
in this context = dihybrid cross = 9:3:4 ratio (4 = white flower)
can distinguish one of single mutants

Question 18

what is recessive epistatic - example, gen

Answer 18

same pathway
intermediate has magenta colour
can distinguish phenotype
if single mutant = end up with pink
if double mutant = looks like single mutant of white alone (so 2 mutations give same phenotype), cannot produce pigment

Question 19

what is a suppressor

Answer 19

mutant allele of a gene that reverses effects of an original mutation

Question 20

describe ex of supressor

Answer 20

ex = function by forming heterodimer
first mutation = changes aa sequence so cannot heterodimerize so
2nd mutation = becomes functional, new allele can interact with modified mutant gene and together suppress the phenotype associated with the gene
Suppressor provides downstream product = can suppress phenotype of mutant

Question 21

what is a modifier

Answer 21

2nd mutation that changes the degree of expression of a mutated gene - phenotype
regulatory function

Question 22

describe ex of modifier

Answer 22

mutations in regulatory sequences
regulates a in absence of b, 30% of gene a expressed
changes degree of phenotypic manifestation

Question 23

what is synthetic lethal

Answer 23

mutations in 2 genes
each often has a weak mutant phenotype
Resulting in lethality

Question 24

give ex of synthetic lethal

Answer 24

multiproptien complexes
mutant a = leads to partial binding
mutant b = leads to partial binding (weak phenotype)
mutant c = leads to impossible binding - none functional so lethal
used to screen for cancer therapy drugs = does not affect normal cells but specifically cancer cells - with cancer promoting mutation

Question 25

describe modified rations between genetically interacting genes

Answer 25

9:3:3:1 = no interaction
9:7 = genes in same pathway
9:3:4 = recessive epistasis
12:3:1 = dominant epistasis
13:3 = supressor has no phenotype
14:2 = suppressor is like mutant
numbers vary on phenotypes and degree of suppression