1. DOMINANTANDRECESSIVE TRAITS

2. DOM I NA NC E T R A I T S :Dominanceingeneticsisarelationshipbetweentwoallelesofagene,inwhichoneallelemasksthephenotype(theexpressionthatwecanseeintheoutside)ofanotheralleleatthesamegenetics. 3. R E C E S S IV E T R A IT S :Arecessivetraitisatraitcausedbyarecessivegene,whichmeansthatsomeonemustinherittwocopiesofthegeneforthetraittomanifest.Whenorganismssuchashumansreproduce,theyproduceyoungwithageneticinheritancefrombothparents,causedbythefusingofhaploidspermwithhaploideggstocreateadiploidorganism.(Inourcasewehave46chromosomes,23comesfromeachparent),soeachchromosomecontainsaseriesofallelesorgeneswhichcodevariousinformation. 4. 5. E X P L A N A T IO N :Whensomeoneisheterozygous,however,oneofthealleleswillremaininactive,andthisallelerepresentsarecessivetrait.GregorMendel(consideredthefatherodgeneticsbeacuseofhisexperimentsonthefields)didmuchofhisworkwithpeas.Inthecourseofhisresearch,helearnedthatpurplewasadominanttraitforflowercolor,meaningthatafloweronlyhadtoinheritonepurplegenetoproducepurpleflowers.Whensomeoneisheterozygousforatrait,thedifferencebetweendominantandrecessivetraitsbecomesmoreimportant,becausethedominanttraitistheonewhichwillmanifest. 6. F O R E XA M P L E :Whentheallelesfrombothparentsarethesame(AAAA),someoneissaidtobehomozygousatthatallele.Ifachildinheritstwodifferentalleles,suchasageneforredhair(RR)andageneforbrownhair(BB),heorsheissaidtobeheterozygousatthatallele:Whensomeoneinheritsthesamealleletwice,,thattraitwillmanifestwhetherornotitisdominant.Whensomeoneisheterozygous,however,oneofthealleleswillremaininactive,andthisallelerepresentsarecessivetrait. 7. 8. E XA M P L E SInthesimplestcase,whereageneexistsintwoallelicforms(Aandb),threecombinationsofgenotypes(alleles)arepossible:AA:Homozygoticdominant.Ab:Heterozygoticdominat.bb:HOmozygoticrecessive.IfAAandbbindividuals(homozygotics)showdifferentformsofthetrait(phenotype),andAbindividuals(heterozygotics)showthesamephenotypeasAAindividuals,thenalleleAissaidtodominateorbedominanttoorshowdominancetoalleleb,andbissaidtoberecessivetoA. 9. E XA M P L E S :1Thelanguageofgeneticsconsistsofsymbolsandrulesforusingthesesymbols.Whenthetraitthatwearestudyingisdominantweuseacapitallettertoshowitssymbol.Whenwerepresenttherecessivetraitfromthesametraitweputthesameletterbutnotcapitalized.EXAMPLE:Ifwehaveatallpeaplantdominativerashortpeaplantitwillberepresentedlikethat:Dominan(tall):TRecessive(short):t2Thefollowinglettersrepresentpairsofalleles.wehavetoindicatewhethereachpairisaheterozygote(hybrid)orhomozygote(purebrid).Laterwecanindicatewhethereachpairwoulddisplayadominantorrecessivephenotype DD:HomozygoticdominantDd:Heterozygoticdominant ss:HmozygoticrecessiveRr:Heterozygoticdominant Tt:Heterozygoticdominantyy:Homozygoticrecessive 10. S OURC ES :Ivegotmyinformationfromtheseplaces:http://www.wisegeek.com/whatisarecessivetrait.htmhttp://en.wikipedia.org/wiki/Dominance_(genetics)Mynotebookandmyownnowledge.