Chapter VIII - Mutation

7/25/2019 Chapter VIII - Mutation

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Mitch B. Forbes

BS Biology IV - A

Chapter VIIIMUTATIONS


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Mutationare changes in the organis that are

heritable an! essentially peranent.

the changing o" the structure o" a gene#resulting in a $ariant "or that ay betransitte! to subse%uent generations#cause! by the alteration o" single baseunits in &NA# or the !eletion# insertion# orrearrangeent o" larger sections o" genesor chroosoes.


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A. Variation in the Genome

Structure or NumericalChanges of the Chromosomes


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Changes in chroosoe nuber can occurby the a!!ition o" all or part o" a chroosoe'aneuploidy(# the loss o" an entire set o"chroosoes 'monoploidy( or the gain o" oneor ore coplete sets o" chroosoes'euploidy(. )ach o" these con!itions is a$ariation on the noral !iploi! nuber o"

chroosoes.


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*. Euploidyre"ers to the changes in$ol$ing the +hole

genoe or the entire set o" chroosoes

Polyploids are organiss +ith the cellcontaining three or ore sets o"chroosoes or genoes.

,hen polyploi!y is !ue to the ultiplicationo" one basic genoe# it is calle!autopolyploidy.

Allopolyploids, on the other han!# arethose in +hich the genoes aing up theultiple sets are not i!entical. )aples o"

the basic types o" euploi!s are/


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Autopolyploidy:Triploids !"# $ bananas# hyacinths# +inesap

apples# )uropean pears

Tetraploids %"# $ potato# al"al"a# co0ee#peanuts

Allopolyploidy: e"amples#a#

Nicotiana ta&acum '. To&acco# (n ) %*#1* 2 13/ Nicotiana sylvestris N. tomentosiformis

'ss4 3n 5 36( 'tt4 3n 5 36(

F*/ 36 I '*3 Is 7 *3 It( / Sterile

Chroosoe&oubling o" F*/ 36 II '*3 IIs 7 *3 IIt ( / Fertile

5 Nicotiana tabacum L.'3n 5 68(


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+aphano&rassica is an eperientalallotetraploi! pro!uce! by 9.&. :arpecheno in*;3< by hybri!i=ing ra!ish 'Raphanus sativusL.( +ith cabbage 'Brassica oleracea(.

1* 2 13/ Raphanus sativus Brassica oleracea

'>>4 3n 5 *8( 'BB4 3n 5 *8(F*/ *8 I '; I

> 7 *3 IB( / Sterile

Chroosoe

&oubling o" F*/ *8 II '; II>

7 ; IIB

( / Fertile1henotype/ ?ea! o" ra!ish an! root o"

cabbage


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Allohe"aploid: e"ample#

Triticuum aestivum read -heat# (n )%(#

1* 2 13/ Triticum monococcum Aegilops speltoides

'AA4 3n 5 *6( 'BB4 3n 5 *6(

F*/ *6 I '< IA 7 < IB( / SterileChroosoe

&oubling o" F*/ *6 II '< IIA 7 < IIB( / Fertile 5

Triticum dicoccum '3n 5 38(

T. dicoccum Aegilops squarrosa

'AABB4 3n 5 38( '&&4 3n 5 *6(


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F*/ 3* I '< IA7 < IB7 < I&( / Sterile

Chroosoe

&oubling o" F*/ 3* II '< IA7 < IB7 < I&( / Fertile5 Triticum aestivum '3n 5 63(


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Table o" Variations in Chroosoe Nuber'Basic Chroosoe Nuber 5 6(

Type ormula

Chromosome Complement

/onoploid n 'ABC&(

0iploid

3n 'ABC&( 'ABC&(Autotriploi

dn 'ABC&( 'ABC&( 'ABC&(

Autotetrapl

oid6n 'ABC&( 'ABC&( 'ABC&( 'ABC&(

Allotetraploid 6n 'ABC&( 'ABC&( 'MNO1( 'MNO1(


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The Origin an! >elationships o"&i0erent 1olyploi!s


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1olyploi!yPolyploidcells an! organiss are those

containing ore than t+o paire!'hoologous( sets o" chroosoes.

1olyploi!y is a coon occurrence inplants --- at least 6


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1hysical Characteristic o" 1olyploi!s

Autopolyploi!sThe physical characteristics o"

autopolyploi!s ay be %uite !istinct "rotheir !iploi! progenitors. Aong the ore

coon physical characteristics are/a( Increase! in!i$i!ual cell si=e# although this

increase ay not eten! to the tissues an!organs4

b( Slo+er gro+th rate an! later aturity than!iploi!s4

c( Thicer lea$es# larger an! "e+er Do+ers an!larger "ruits than !iploi!s4


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>e!uce! "ertility n $arying !egrees ' the re!uctionin the "ertility !ue to eiotic abnoralities#especially that on hoologous paiing# o" the

autoplyploi!s !uring gaete "oration.( an!)istence# in general# o" an optiu range o"

polyploi!y beyon! +hich gro+th ay be !epresse!+ith increasing chroosoe nuber.

For eaple# the chroosoe nuber an! the plantheight in tiothy plants are gi$en belo+.

Chromosome Num&er Plant 1eight

!n E

%n


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Allopolyploi!sAllopolyploi!s are "ertile an! they possess any

o" the physical characteristics o" the

autopolyploi!s. Allopolyploi!y has beenresponsible "or the "oration o" ne+ species

)aple,heat

Tobacco>aphanobrassica


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3. Aneuploi!yoccurs +hen one or ore chroosoes o"

a noral set 'genoe( are lacing or arepreset in ecess.

. The nuclei# there"ore# +ill contain

chroosoes +hose nubers are notultiples o" genoe. In other +or!s# theaneuploi!s are characteri=e! by incopletegenoes


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Types o" Aneuploi!y

Type ormula

Monosoic 3n-*

Nullisoic 3n-3&ouble Monosoic 3n-*-*

Trisoic 3n73

Tetrasoic 3n73

&ouble Trisoic 3n7*7*


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. Changes in Chromosome Structureor Chromosomal A&errations


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Changes in the genetic in"oration ayalso be cause! by the changes inchroosoe structure.

Structural aberrations are cause! by breasin the chroosoe or the chroati!. )achbrea pro!uces t+o en!s# +hich ay then

"ollo+ three alternati$e paths.*. Broen en!s ay reain ununite!# lea!ing to

e$entual loss o" the segent +hich !oes notinclu!e the centroere.

3. Sae broen en!s ay reunite or restituteie!iately.

. Broen en!s a Goin those pro!uce by a!i0erent brea# causing an echange or a

nonrestitutional union.


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&eHciencies or &eletions>epresents a loss o" a segent o" the

chroosoe


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The genetics e0ects o" !eHcienciesinclu!e the "ollo+ing/

&eHciencies "or a consi!erable nuber o"loci result in lethality.Non-lethal !eHciencies ay result I

pseu!o-!oinance.Crossing-o$er is copletely absent in the

!eHcient region.&eHciencies ay pro!uce uni%ue

phenotypic e0ect o" their o+n.


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Follo+ing are soe eaple o"chroosoal !eHciencies in an/

1hila!elphia 33 chroosoe is a !eHciency"or a large portion o" the long archroosoe 33. It is associate! +ithchronic yeloi! leueia.

Cri-!u-chat syn!roe is a !eletion in theshort ar o" chroosoe . It is!istinguishe! by cat-lie cry !uring in"ancy#uni%ue "acial "eatures an! $arious "ors o"

physical an! ental retar!ation.


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&uplications or >epeatsoccur +hen a

section o" thechroosoe is inecess o" the noral

aount. Therepeate! section o"chroosoalaterial ay be

present in one pairo" hoologouschroosoes oray ha$e been

transpose! to a


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The genetic e0ects o" !uplications inclu!ethe "ollo+ing/

&uplications o" recessi$e alleles pro!uce+il! type phenotypes# e.g.# !uplications o"8ermilion '$( allele in &rosophila pro!uce!the +il! type phenotype.

Copleentary genes or ultiple "actors#+hich a0ect the sae character# arebelie$e! to ha$e arisen initially as!uplications o" single genes.


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In$ersionis the rotation o" the chroosoes

segent to a "ull *8 !egrees

There are t+o types o" in$ersion ---paracentric an! pericentric in$ersion.

a# Paracenric in8ersion occurs +hen thecentroere is not inclu!e! in the in$erte!segent.

Pericentric in8ersion occurs +hen the

in$erte! segent inclu!es the centroere.


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There are threegenetic

conse%uences o"in$ersions

*. In$ersionhoo=ygotes ha$e

noral beha$ior#+ith coplete"ertility but +ith ane+ linage or!er.

3. In$ersionhetero=ygotes arepartially orcopletely sterile.

. Crossing-o$er is


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Interchange or >eciprocalTranslocation

Translocationoccurs +hen single breasinto t+o nonhoologous chroosoespro!uce an echange o" chroosoesections bet+een the.


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The "ollo+ing are the genetic conse%uenceso" reciprocal translocation/

In hoo=ygotes# there +ill be altere! linageassociations "or the genes containe! inechange segents.

In hetero=ygotes# partial sterility occurs an!

this is !ue to chroosoe segregation !uringAnaphase I# +hereby gaetes +ith !uplicationan! !eHciencies o" soe loci are pro!uce!.Such gaetes ay be lethal.


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C. 9ene Mutation


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9ene Mutation

The only consistent lin bet+eengenerations o" cells in &NA an!# there"ore#any utation is basically a change in &NA.Anyone o" the "our nitrogen bases o" the

&NA ren!ers itsel" to changes that coul!alter the &NA olecule.

is a peranent alteration in the &NAse%uence that aes up a gene# such that

the se%uence !i0ers "ro +hat is "oun! inost people.

/utations range in si=e4 they can a0ectany+here "ro a single &NA buil!ing bloc

'base pair( to a large segent o" a


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Microlesions/ Base 1air Substitution

This utation in$ol$es only one nucleoti!e pair#

eaning# there is only one nucleoti!e pair!i0erence bet+een the +il! type an! the utantallele.Transition mutation is the substitution o" a purine

+ith another purine or a pyrii!ine +ith anotherpyrii!ine# e.g.# a!enine by guanine or thyine bycytosine.

Transversion mutation is the substitution o" purine

by pyrii!ine or $ice $ersa# e.g.# guanine b.ycytosine or thyine by a!enine.


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Fraeshi"t Mutations

A!!ition or !eletion o" single nucleoti!e or "e+nucleoti!es causes "raeshi"t utation. &uringthe rea!ingJ o" the genetic essage# Cric# etal. propose! that the rea!ing starte! "ro a

He! point. An insertion or !eletion o" one ort+o nucleoti!e pairs +oul! pro!uce a shi"t inthe rea!ing "raeJ an! such shi"t +oul! resultin utation.

Fraeshi"t utation occurs ost "re%uentlyregions +here a onotonous &NA se%uence#such as AAAAAA in one stran! o" TTTTTT in theother. Soeho+ this "a$ors stutteringJ in the

process o" &NA synthesis# lea!ing to a!!ition


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Mutator 9enes

In a!!ition to physiological "actors# it +asobser$e! that utation rate "re%uently ightbe attribute! to speciHc mutator genes.Mutator genes +ere obser$e! in a $ariety o"

organiss# inclu!ing proaryotes. Many o"these are belie$e! to be associate! +ith &NApolyerase or siilar en=yes in$ol$e! in &NAreplication an! repair.

The total utation rate is increase! se$eralties.


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Transposons or Kuping 9enesA transposa&le element'TEor transposon( is

a &NA se%uence that can change its position +ithina genoe# soeties creating orre$ersing utations an! altering the cellLs genoesi=e.

Barbara McClintoc stu!ie! in *;* the o$ablegenetic eleents in corn# no+ re"erre! to as the Ac-&ssyste.

I" these t+o loci becoe !issociate! "ro each other#

the utant cell an! all its !aughter cells containingthe reaining locus are colore!. The locus reo$e! iscalle! 0issociation 0s#gene on chroosoe ;. Thisgene can cause breaage in chroosoe regions nearit.


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The "ollo+ing are the properties o" the 0sgene/

*. I" 0sis ne$er !issociate! +ith thea!Gacent locus# the ernel is +hite.

3. I" it is !issociate! !uring ernel "oration#the ernel has colore! sectors or !ots on a

+hite bacgroun!.

. I" it is !issociate! be"ore ernel "oration#the ernel an! later generation o" plantsare copletely colore!.


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McClintoc "urther obser$e! that 0s +ere onlyacti$e in the presence o" an Acti8ator Ac#gene that coul! be locate! on any o" the other

chroosoes.One special attribute o" 0s an! Acis their

transposibility.

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Chapter VIII - Mutation