for connect with final answers gen. int 2 in class lecture 6 gene interaction - part 2

7/24/2019 For Connect With Final Answers Gen. Int 2 in Class Lecture 6 Gene Interaction - PART 2

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Gene Interaction-PART 2


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Todays lecture (0122)

Mendels Dihybrid Cross - the 9:3:3:1 ratio

Revisited Concept of genetic interaction between alleles at

two dierent loci!

"he 9:3:3:1 ratio no gene interaction

#pistasis "he 9:$ ratio genes in the sa%e pathway

&'ppressors( %o)diers and &ynthetic lethals!

*enetrance and e+pressivity


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Mendels dihybrid cross

Mendels dihybrid cross:

- two dierent genes ,R,ror Y(y

- each gene had an independent phenotypiceect: seed shape ,ro'nd or wrin.led

and seed color ,yellow or green- i!e! / genes( / phenotypes and genes do not

interact ,Yoryaect only seed color and do notaect seed shape and vice versa for the Rand r

alleles for seed shape


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Dihybrid ross


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Dihybrid ross

R/-0 Y/-: ro'nd( yellow 9R/-0y/y: ro'nd( green 3r/r0 Y/-: wrin.led( yellow 3r/r0y/y: wrin.led( green 1

ll of the 12 genotypes of the /fall

in these 4 genotype categories:


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Dihybrid ross

5n general( for a dihybrid cross between two do'ble

hetero6ygotes ,hetero6ygo's at two genetic loci:

7a 0 87b 7a 0 87b

enotype Categories:7- 0 87- : 97- 0 b7b : 3a7a 0 87- : 3

a7a 0 b7b : 1


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Interactions bet!een alleles o" t!odi#erent $enes enes %ay not always act independently in their

phenotypic e+pression

enes at one loc's can aect genes at another loc'sand prod'cts of genes at dierent loci co%bine toprod'ce a new phenotype ; ene interaction

ene interactions change Mendelian phenotypic

ratios ,do not get 9:3:3:1 ratio


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Interactions bet!een alleles o" t!odi#erent $enes

The %&'&'&1 ratio& no $ene interaction

#g: s.in coloration in Corn sna.es:


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>range-blac. ,ca%o'=age : o+7-0 b+7-

8lac. ,lac.s orange : o 7o; b+7-

>range ,lac.s blac. : o+7-0 b 7b

lbino ,no blac.( no orange: o 7o 0 b 7b

o+7o+; b7b ,orange x o7o ;b+/b,blac.

1: o+/o ; b+/b ,ca%o'=aged

&elf 1 o+/o ; b+/b x o+/o ; b+/b

/: 9 o+7-0 b+7- ,ca%o'=aged

3 o+7-0 b7b ,orange

3o7o; b+7- ,blac.


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Interactions bet!een alleles o" t!odi#erent $enes The %& ratio+ $enes in sa.e ,ath!ay:

#g: 8l'e-white =ower color in harebell plants:

- ?ild-type =ower color is bl'e and %'tant =ower color is white

- 8l'e color is d'e to pig%ent called anthocyanin!

- nthocyanin absorbs light of all wavelengths e+cept bl'e and

re=ects bl'e which is the color of =ower seen!

- nthocyanin %ade fro% prec'rsors byen6y%es

- 5f en6y%e for anthocyanin is defective:

o anthocyanin not f'nctional(

o prec'rsors do not absorb light b't re=ect itbac.

o =ower appears white


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Interactions bet!een alleles o" t!odi#erent $enes "he 9:$ ratio( genes in sa%e pathway:

- 8ioche%ical pathway for synthesi6ing anthocyanin:

gene w1@ gene w2@

prec'rsor 1 en6y%e 1 prec'rsor / en6y%e / anthocyanin,bl'e

- M'tation in either w1@ or w2@;


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Interactions bet!een alleles o" t!odi#erent $enes "he 9:$ ratio( genes in sa%e pathway:

* w17w10 w2@7w2@,white w1@7w1@ 0 w27w2,white

a%etes w1;w2@ w1@0 w2

1 w1@7w10 w2@7w2 ,bl'e

&elf 1 w1@7w10 w2@7w2,bl'e w1@7w10 w2@7w2,bl'e

a%etes w1@0w2+ w1@0w2 w1;w2@ w1;w2 w1@0w2+ w1@0w2 w1;w2@ w1;w2

/ 9712 w1@

7-

0 w2@

7-,bl'e 9 ?ild-type

3712 w1@7-0 w27w2,white &ingle %'tant

3712 w17w10 w2@7-,white $ &ingle %'tant

1712 w17w10 w27w2 ,white Do'ble


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The %&'& ratio& Recessi3e 4,istasis

- abrador dogs can be blac.( brown or yellow!


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"he 9:3:4 ratio: Recessive #pistasis

- Coat color deter%ined by interaction between / gene loci!

- ene loc's 1: type of dar. s.in pig%ent:

allele B: blac. pig%ent( do%inant

allele b:brown pig%ent( recessive

- ene loc's /: deposition of the pig%ent in the shaft of the hair:

allele E:deposition of pig%ent ,blac. or brown(do%inant

allele e:prevents deposition of pig%ent ,yellow(

recessive

- enotype eeat the second loc's %as.s e+pression of the blac.and brown alleles at the )rst loc's! ,i!e! -/-( e/e; yellow

- #pistasis is an eect of gene interaction s'ch that onegene

%as.s ,hides the eect of another gene at a dierent loc's!


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"he 9:3:4 ratio: Recessive #pistasis ,coat color of abrador dogs

Cross a blac. labrador ho%o6ygo's for the do%inant alleles at bothgene loci with a yellow labrador ho%o6ygo's for the recessivealleles at both gene loci

* B/B; E/E,8lac. + b/b; e/e ,Bellow

Gametes B;E b;e1 B/b; E/e ,8lac.

&elf 1 B/b;E/e ,8lac. + B/b;E/e ,8lac.

/ 9712 B7-0E7- ,8lac. 9

3712 b7b0E7- ,8rown 3

3712 B7-0e7e ,yellow

1712 b7b0e7e ,yellow 4 ,-7-0e/e

Phenoty,ic ratio lac*& ro!n& 5ello! %&'&

R4AD A6T P4TA7 PIGM48T 958T:49I9 I8 764-454D


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"he 9:3:4 ratio: Recessive #pistasis

- enotype eeat the second loc's %as.s e+pression of the blac.and brown alleles at the )rst loc's!

- #pistasisis an eect of gene interaction s'ch that onegene%as.s ,hides the eect of another gene at a dierent loc's!

-ene that does the %as.ing ; epistaticgene ,pig%entdeposition

- ene whose eect is %as.ed ; hypostaticgene ,coat colorpig%ent

- Recessiveepistasis: Recessive allele at second loc's ,no pig%ent

deposition overrides pig%ent color phenotype deter%ined by)rst loc's!


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"he 1/:3:1 ratio: Do%inant #pistasis:

#g: *etal coloration in o+gloves


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"he 1/:3:1 ratio: Do%inant #pistasis:

#g: *etal coloration in o+gloves- *etal coloration deter%ined by interaction between / gene loci!

- ene loc's 1: intensity of red pig%ent in petal:

allele d: light red color( recessive ,seen

nat'rallyallele D:dar. red color( do%inant ,%'tant

- ene loc's /: distrib'tion of pig%ent in petals ,light or dar. red:

allele w:pig%ent synthesi6ed thro'gho't petal(

recessiveallele W:white petal with red throat spots(

do%inant

- enotype W/-at the second loc's %as.s distrib'tion of the redpig%ent thro'gho't petal!,i!e! -7-0 W/-; white petals with spots


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"he 1/:3:1 ratio: Do%inant #pistasis ,*etal coloration ino+gloves

Cross =owers that have white petals and red throat spots(ho%o6ygo's for the do%inant alleles at both gene loci with a =owerwith light red petals( ho%o6ygo's for the recessive alleles at bothgene loci

* D/D; W/W,?hite with spots + d/d; w/w ,ightRed

Gametes D;W d;w

1 D/d;W/w ,?hite with spots

D/d;W/w ,?hite with spots + D/d;W/w ,?hite with spots

/ 9712 D7-0W7- ,?hite with spots 1/,-7-0W7W 3712 d7d0W7- ,?hite with spots

3712 D7-0w7w ,Dar* red 3

1712 d7d0w/w ,ight red 1

Phenoty,ic ratio hite !ith s,ots& Dar* red& ight red12&'&1


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&'ppressors-

A .utant allele o" one $ene that re3erses the e#ect o" a.utation at another $ene+ resultin$ in !ild-ty,e,henoty,e

- &'ppressor gene and target gene %'st interact at f'nctionallevel in wild-type state

#g: Drosophiaeye color

ene loc's 1: #ye color:

allelepd: p'rple color( recessive ,%'tant

allelepd+

:red color( do%inant ,wild-type ene loc's /: &'ppressor ,no independent phenotype:

allele s!:s'ppressespd( recessive

allele s!+:


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&'ppressors: ,Drosophiaeye color

Cross a ho%o6ygo's p'rple-eyed =y with a ho%o6ygo's red-eyed

=y carrying the s'ppressor

* pd/pd; s!+/s!+,*'rple + pd+/pd+; s!/s! ,Red

Gametes pd; s!+ pd+; s!

1 pd+/pd; s!+/s! ,Red

pd+/pd; s!+/s! ,Red+ pd+/pd; s!+/s! ,Red

/ 9712pd+7-0s!+7- ,Red

3712pd+7-0s!7s!,Red 13

1712pd7pd0s!7s! ,Red do'ble%'tant

3712pd7pd0 s!+7- ,p'rple 3


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Interactions bet!een alleles o" t!odi#erent $enes &'ppressors: Molec'lar Mechanis%

1! 5f %'tation bloc.s a %etabolic pathway( s'ppressor bypassesthe bloc.

,eg: by rero'ting into inter%ediates si%ilar to those in thepathway

beyond the bloc.


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&'ppressors: Molec'lar %echanis%

/:

%@

7%! s@

7s + %@

7%!s@7s

%@7- ! s@7-: active 9%7%! s@7s: active/ 14%@7% ! s7s: active/

%7% ! s7s: active


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Interactions bet!een alleles o" t!odi#erent $enes Modi)ers:

- 5nstead of one gene %as.ing the phenotypic eect of anothergene( it %ay %odify the e+pression of the second gene!

#g: Coat color in %ice:ene oc's 1: ene for Coat color:

llele B; blac. coatllele b; brown coat

ene oc's /: 5ntensity of coat color:llele D; f'll color ,blac. or brownllele d; dil'ted e+pression of Bor balleles


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Interactions bet!een alleles o" t!odi#erent $enes Modi)ers:

1 B/b; D/d ,8lac.

&elf 1 B/b;D/d ,8lac. + B/b;D/d,8lac.

/ 9712 B7-0 D7- ,8lac.

3712 b7b0 D7- ,8rown

3712 B7-0 d7d ,dil'te blac.

1712 b7b0 d7d ,dil'te brown

Phenoty,ic ratio lac*& ro!n& dilute blac*& dilutebro!n %&'&'&1

llele at loc's for intensity of coat color doesnt %as.( b't%odi)es( the eect on coat color


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Interactions bet!een alleles o" t!odi#erent $enes 9ynthetic 7ethals:

1! Crossing two single %'tants res'lts in do'ble %'tants ,eg: aand bare

%'tant alleles at / dierent gene loci that are lethal:

self the 1: a+7a 0 b+7b a+7a 0 b+7b

/: a+7- 0 b+7- : 9

a+7- 0 b7b: 3

a7a0 b+7- : 3

a7a0 b7b: 1 ethal

Ratio ; 9:3:3


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Interactions bet!een alleles o" t!odi#erent $enes &ynthetic ethals: Molec'lar Mechanis%

1! D'plicate syste%s in cells as a Ebac.'pF! 5f n'll %'tations inboth

syste%s -G


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Penetrance and 4;,ressi3ity *enetrance ; H of individ'als with a given allele that e+press

the phenotype associated with that allele

5f 1II individ'als have an allele for bl'e eye color and all havebl'e eyes( the allele is 1IIH penetrant into the phenotype

5f not( the allele is inco%pletely penetrant

Reasons:

- #nviron%ent

- 5n='ence of other interacting genes

- 5f it is a %'tant allele( the eects on

phenotype %ay be s'btle

do%inantallele is not

f'lly penetrant


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Penetrance and 4;,ressi3ity #+pressivity: Meas'res the degree7e+tent of phenotypic

e+pression of a given allele ,i!e! intensity of phenotype

#g: piebald spotting in beagles! #ach has allele for piebaldspotting b't there is variation in e+tent of spotting!


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Penetrance and 4;,ressi3ity Penetrance 3s< e;,ressi3ity


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7earnin$ utco.esBo' sho'ld be able to:

#+plain the concept of gene interaction with respect to

interactions between alleles at two dierent gene loci! &olve genetic proble%s based on genetic interaction

between two genetic loci!

#+plain the dierence between Recessive and

Do%inant epistasis! Describe the %olec'lar %echanis%s 'nderlying the

eects of %odi)er and s'ppressor alleles!

#+plain the dierence between penetrance and

e+pressivity!


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7earnin$ utco.esBo' sho'ld be able to:

Describe the %olec'lar %echanis%s 'nderlying the

eects of %odi)er and s'ppressor alleles! #+plain the dierence between penetrance and

e+pressivity!

for connect with final answers gen. int 2 in class lecture 6 gene interaction - part 2

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