Download GENE

LECTURE 11: FROM GENE TO PHENOTYPE II
chapter 6
questions & concepts
genes & gene products
allele interactions
gene & protein interactions
chi-square applications
exam 1: problems
GENE & PROTEIN INTERACTIONS
how do you identify interacting genes?
1. generate new mutant alleles for a trait of
interest by mutagenesis
2. test mutant alleles to determine if they
represent alleles of multiple genes by
(a) mapping & (b) complementation
3. combine mutant alleles to identify epistatic
interactions
GENE & PROTEIN INTERACTIONS
a complementation test will reveal allelic
relationships  1 gene (below)...
1. dominance / recessiveness
2. semi-dominance = incomplete dominance
3. co-dominance (e.g.: IA & IB of ABO system)
4. multiple alleles (e.g.: IA, IB & i of ABO system)
5. conditional (e.g.: temperature sensitive)
6. lethality
7. sterility
... or give wild type phenotypes  2 genes
COMPLEMENTATION TEST
are mutations allelic (1 gene) or not (2 genes)?
test by making pair-wise crosses between mutants
COMPLEMENTATION TEST
COMPLEMENTATION TEST
 gene
 genes
COMPLEMENTATION TEST
... because the 2 mutations are in different genes
GENE & PROTEIN INTERACTIONS
what is epistasis?
text (1): a situation in which the differential
phenotypic expression of a genotype at one locus
depends on the genotype at another locus
text (2): a mutation that exerts its expression
while canceling the expression of the alleles of
another gene
Herr Doktor Professor: interactive expression of
alleles at two (or more) genes (both of the text
definitions are limiting)
GENE & PROTEIN INTERACTIONS
Mendelian phenotypic ratios
GENE & PROTEIN INTERACTIONS
Mendelian dihybrid ratio
io…
ys…
is…
is…
es…
es…
es…
e)…
e)…
GENE & PROTEIN INTERACTIONS
A_ B_
9
9
A_ bb
3
3
aa B_
3
3
3
12
9
9
3
4
6
1
1
15
9
10
aa bb
1
1
1
7
6
13
3



Mendelian dihybrid ratio
parallel pathways
dominant epistasis
recessive epistasis
duplicate additive genes
duplicate dominant genes
duplicate recessive genes
recessive suppression (1)
recessive suppression (2)
PARALLEL PATHWAYS
bw+/_; st+/_ 9
bw+/_; st/st 3
bw/bw;
+
st /_
3
bw/bw; st/st 1
9:3:3:1
PARALLEL PATHWAYS
o+/_; b+/_ 9
o+/_; b/b 3
o/o;
+
b /_
3
o/o; b/b 1
9:3:3:1
DOMINANT EPISTASIS
D/_; W/_ 9
d/d; W/_ 3
D/_; w/w 3
d/d; w/w 1
12 : 3 : 1
W  D gene expression
RECESSIVE EPISTASIS
w+/_; m+/_ 9
w+/_; m/m 3
w/w; m+/_ 3
w/w; m/m 1
9:3:4
DUPLICATE DOMINANT GENES
A1/_; A2/_
9
A1/_; a2/a2 3
a1/a1; A2/_ 3
a1/a1; a2/a2 1
15 : 1
1 dominant allele  pigment
DUPLICATE RECESSIVE GENES
(aka COMPLEMENTARY GENE ACTION)
C/_; P/_ 9
C/_; p/p 3
c/c; P/_ 3
c/c; p/p 1
9 : 7 1 recessive allele  pigment
REGULATING GENE & TARGET INTERACTION
r+/_; a+/_ 9
r/r; a+/_ 3
r+/_; a/a 3
r/r; a/a
9:7
1
(A POSSIBLE) SUPPRESSION MECHANISM
RECESSIVE SUPPRESSION
pd+/_; su+/_ 9
pd+/_;
su/su 3
pd/pd; su+/_ 3
pd/pd; su/su 1
13 : 3
pd+
su+
mechanism for genotype
 not explained by model
pd
su+
pd
su
io…
ys…
is…
is…
es…
es…
es…
e)…
e)…
GENE & PROTEIN INTERACTIONS
A_ B_
9
9
A_ bb
3
3
aa B_
3
3
3
12
9
9
3
4
6
1
1
15
9
10
aa bb
1
1
1
7
6
13
3



Mendelian dihybrid ratio
parallel pathways
dominant epistasis
recessive epistasis
duplicate additive genes
duplicate dominant genes
duplicate recessive genes
recessive suppression (1)
recessive suppression (2)
MODIFIERS
modifier mutations influence expression of a
mutation at a second locus
broadly used term (text gives a few examples)
gene activity can be modified by...
up- or down-regulation
enhancement or suppression
SYNTHETIC LETHALS
PENETRANCE & EXPRESSIVITY
penetrance: the % of individuals of given genotype
that exhibit a phenotype... a population measurement
expressivity: the extent to which a given genotype is
expressed at the phenotypic level... in each individual
PENETRANCE & EXPRESSIVITY
can be due to...
1. environmental factors
2. genetic factors
3. unknown / difficult to measure (text) ???
e.g., the rover / sitter foraging polymorphism
POLYGENY
GENE 

GENE   PHENOTYPE
GENE 
BIOCHEMICAL PATHWAY:
      PHENOTYPE
COMPETITION / INHIBITION:


  PHENOTYPE


ENZYME CATALYSIS:


    PHENOTYPE
PLEIOTROPY
PHENOTYPE 

GENE  PHENOTYPE 
 PHENOTYPE 
SEQUENTIAL PHENOTYPES: GENE      
RELATED PHENOTYPES:
UNRELATED PHENOTYPES:


GENE  




GENE    
GENE & PROTEIN INTERACTIONS








CHI-SQUARE APPLICATIONS
example question on p. 209
true-breeding P yellow x red
petal plants  all orange petal
F1. F1 are bred & F2 are...
red
orange
yellow
total
77
182
61
320
with 3 phenotypes, reasonable hypotheses are...
H1 = incomplete dominance... 1:2:1 ratio
E = 80 G1/G1 + 160 G1/G2 + 80 G2/G2
2 = 7.6, P < 0.025 (2.5%),  H1 
CHI-SQUARE APPLICATIONS
example question on p. 209
true-breeding P yellow x red
petal plants  all orange petal
F1. F1 are bred & F2 are...
red
orange
yellow
total
77
182
61
320
with 3 phenotypes, reasonable hypotheses are...
H2 = recessive epistasis of r on Y & y... 9:3:4 ratio
E = 180 Y/_; R/_ + 60 y/y; R/_ + 80 [Y/_; r/r + y/y; r/r]
2 = 0.15, P > 0.9 (90%),  H2 
PRACTICE PROBLEMS
you should be able to do
CH6, p. 214
# 1 - 50