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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?

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lecture 11 from gene to phenotype ii
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
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 interactions3
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
COMPLEMENTATION TEST
  • are mutations allelic (1 gene) or not (2 genes)?
  • test by making pair-wise crosses between mutants
complementation test6
COMPLEMENTATION TEST

 gene

 genes

complementation test7
COMPLEMENTATION TEST
  • ... because the 2 mutations are in different genes
slide8

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 interactions9
GENE & PROTEIN INTERACTIONS

Mendelian phenotypic ratios

gene protein interactions10
GENE & PROTEIN INTERACTIONS
  • Mendelian dihybrid ratio
slide11

GENE & PROTEIN INTERACTIONS

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
PARALLEL PATHWAYS

bw+/_; st+/_ 9

bw+/_; st/st 3

bw/bw; st+/_ 3

bw/bw; st/st 1

9 : 3 : 3 : 1

parallel pathways13
PARALLEL PATHWAYS

o+/_;b+/_9

o+/_; b/b 3

o/o; b+/_ 3

o/o; b/b 1

9 : 3 : 3 : 1

dominant epistasis
DOMINANT EPISTASIS

D/_; W/_ 9

d/d; W/_ 3

D/_; w/w 3

d/d; w/w 1

12 : 3 : 1

W  Dgene expression

recessive epistasis
RECESSIVE EPISTASIS

w+/_; m+/_ 9

w+/_; m/m 3

w/w; m+/_ 3

w/w; m/m 1

9 : 3 : 4

duplicate dominant genes
DUPLICATE DOMINANT GENES

A1/_; A2/_ 9

A1/_; a2/a23

a1/a1; A2/_ 3

a1/a1; a2/a21

15 : 1

1 dominant allele pigment

duplicate recessive genes aka complementary gene action
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
REGULATING GENE & TARGET INTERACTION

r+/_; a+/_ 9

r/r; a+/_ 3

r+/_; a/a 3

r/r; a/a 1

9 : 7

recessive suppression

su+

pd+

pd

pd

su+

su

RECESSIVE SUPPRESSION

pd+/_; su+/_ 9

pd+/_; su/su 3

pd/pd; su+/_ 3

pd/pd; su/su 1

13 : 3

mechanism for genotype

 not explained by model

slide21

GENE & PROTEIN INTERACTIONS

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
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
penetrance expressivity
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 expressivity25
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
slide26

GENE 

GENE  PHENOTYPE

GENE 

BIOCHEMICAL PATHWAY:  PHENOTYPE

COMPETITION / INHIBITION:PHENOTYPE

ENZYME CATALYSIS:PHENOTYPE

POLYGENY

slide27

PHENOTYPE

GENE PHENOTYPE

PHENOTYPE

PLEIOTROPY

SEQUENTIAL PHENOTYPES: GENE   

RELATED PHENOTYPES: GENE 

UNRELATED PHENOTYPES: GENE 

gene protein interactions28
GENE & PROTEIN INTERACTIONS

chi square applications
CHI-SQUARE APPLICATIONS

red 77

orange 182

yellow 61

total 320

  • example question on p. 209
  • true-breeding P yellow x red petal plants  all orange petal F1. F1 are bred & F2 are...
  • with 3 phenotypes, reasonable hypotheses are...

H1 = incomplete dominance... 1:2:1 ratio

E = 80G1/G1 + 160G1/G2 + 80G2/G2

2 = 7.6, P < 0.025 (2.5%),  H1 

chi square applications30
CHI-SQUARE APPLICATIONS

red 77

orange 182

yellow 61

total 320

  • example question on p. 209
  • true-breeding P yellow x red petal plants  all orange petal F1. F1 are bred & F2 are...
  • with 3 phenotypes, reasonable hypotheses are...

H2 = recessive epistasis of ron 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
PRACTICE PROBLEMS

you should be able to do

CH6, p. 214

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