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Selectively Breeding Sheep Name _________________________ Part 1: Natural Selection and Selective Breeding Whatisnaturalselection? __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ Whatisselectivebreeding? __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ Whataretheadvantagesofselectivebreeding? __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ Giveanexampleofselectivebreedinganddescribewhattraitmightbeselectedforbythebreeder. __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ Part 2: Using Punnett Squares in Sheep Breeding Imagineyouareasheepfarmerandthereisastrangedisorderthatisaffectingthelambsthatare borninyourflock.Theparentsheeparehealthy,butthelambshavebentlimbsandtwistedspines. Manyofthemaredying,whichwilldrasticallyreduceyourincometothefarmandthelongevityof yourflock.Howcanyoumakewisematingdecisionstopreventthebirthsofthesesicklambs? SpiderLambSyndrome(SLS)insheepisarecessivegeneticdisorder.Itcausesskeletaldeformities includingbentlimbsandtwistedspines.ItisdifficultforsheepbreederstoeliminatetheriskofSLS inaflockbecauseparentsofSLSlambsdonotexhibitanysymptoms.Thisisarecessivedisorder, sobothparentsmustcarryarecessivealleleinorderforthelambtobeaffected. BreedershavethedifficulttaskofusingacombinationofselectivebreedingtechniquesandDNA teststoensurehealthylambs.DNAtestscanbeexpensive,soinsteadofpurchasingDNAtestsfor anentireflock,breederscantestcertainsheepandusePunnettSquarestopredicttheprobability ofothersheepintheflockofcarryingrecessivealleles. 1 Selectively Breeding Sheep (continued) 1. YoumatetwosheepthatarecarriersforSLS,whichmeansboththeramandtheewehave onedominantalleleandonerecessiveallele.FilloutthePunnettSquare. N n N n PossibleCombinations NN=HealthySheep Nn=HealthySheep,buta“carrier”oftheSLSgene nn=LambwithSLS WhatistheprobabilitythattheoffspringwillhaveSLS? Whatistheprobabilitythattheoffspringwillbecarriers? DoyouthinkthatbreedersshouldmatetwoSLScarriers?Whyorwhynot? 2. Youmateasheepthatdoesnotcarryarecessivespiderallelewithacarriersheep.Fillout thePunnettSquare. N N N n 2 Selectively Breeding Sheep (continued) WhatistheprobabilitythattheoffspringwillhaveSLS? Whatistheprobabilitythattheoffspringwillbecarriers? DoyouthinkthatbreedersshouldmateaRRsheepwithacarrier?Whyorwhynot? 3. Youbuyahealthyramfromaneighboringfarm,andyoudonotknowhisgenotype.You matehimwithaSLScarrierandthelambisbornwithSLS. FillinthePunnettSquarewiththegenotypeoftheramandhisoffspring. Ram _____ _____ N n 3 Selectively Breeding Sheep (continued) 4. ArelativelysimplegenetictestisavailableforSLS.Accordingtotheinformationbelow,how muchwoulditcosttotestananimalforSLS?Ifyouhavealargeflockandalimitedbudget, whichsheep(ramsorewes)doyouthinkyoushouldselectfortestingandwhy? __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________ AgelelectrophoresisshowingDNAbands forhomozygousNormal(NN),heterozygous carriers(Nn),andhomozygousSLS(nn) sheep. CostsassociatedwithgenetictestsavailablefromUniversityofCaliforniaDavisVeterinaryGeneticsLaboratory. 4 Selectively Breeding Sheep Name _________________________ Part 1: Natural Selection and Selective Breeding Whatisnaturalselection? Naturalselectionisalsoknownasnaturalbreeding.Animals/plantshavefreechoiceinwhoto breed/reproducewith. Whatisselectivebreeding? Selectivebreedingisalsoknownasartificialselectionorunnaturalselection.Itistheprocessby whichhumansbreedplantsandanimalsforparticulartraits. Whataretheadvantagesofselectivebreeding? Breedersgettoselectwhichtraitstheywantintheirlivestock. Giveanexampleofselectivebreedinganddescribewhattraitmightbeselectedforbythebreeder. Answerswillvary.Arabbitbreederchoosestobreedtherabbitsthathavethebestmarkings. Part 2: Using Punnett Squares in Sheep Breeding Imagineyouareasheepfarmerandthereisastrangediseasethatisaffectingthelambsthatare borninyourflock.Theparentsheeparehealthy,butthelambshavebentlimbsandtwistedspines. Manyofthemaredying,whichwilldrasticallyreduceyourincometothefarmandthelongevityof yourflock.Howcanyoumakewisematingdecisionstopreventthebirthsofthesesicklambs? SpiderLambSyndrome(SLS)insheepisarecessivegeneticdisorder.Itcausesskeletaldeformities includingbentlimbsandtwistedspines.ItisdifficultforsheepbreederstoeliminatetheriskofSLS inaflockbecauseparentsofSLSlambsdonotexhibitanysymptoms.Thisisarecessivedisorder, sobothparentsmustcarryarecessivealleleinorderforthelambtobeaffected. BreedershavethedifficulttaskofusingacombinationofselectivebreedingtechniquesandDNA teststoensurehealthylambs.DNAtestscanbeexpensive,soinsteadofpurchasingDNAtestforan entireflock,breederscantestcertainsheepandusePunnettSquarestopredicttheprobabilityof othersheepintheflockofcarryingrecessivealleles. 1 Selectively Breeding Sheep (continued) 1. YoumatetwosheepthatarecarriersforSLS,whichmeansboththeramandtheewehave onedominantalleleandonerecessiveallele.FilloutthePunnettSquare. N n N NN Nn n Nn nn PossibleCombinations NN=HealthySheep Nn=HealthySheep,buta“carrier”oftheSLSgene nn=LambwithSLS WhatistheprobabilitythattheoffspringwillhaveSLS? Thereisa25%chancetheoffspringwillhaveSLS. Whatistheprobabilitythattheoffspringwillbecarriers? Thereisa50%chancetheoffspringwillcarrytheSLSallele. DoyouthinkthatbreedersshouldmatetwoSLScarriers?Whyorwhynot? Answerswillvary. 2. Youmateasheepthatdoesnotcarryarecessivespiderallelewithacarriersheep.Fillout thePunnettSquare. N N N NN NN n Nn Nn 2 Selectively Breeding Sheep (continued) WhatistheprobabilitythattheoffspringwillhaveSLS? Thereisa0%chancetheoffspringwillhaveSLS. Whatistheprobabilitythattheoffspringwillbecarriers? Thereisa50%chancetheoffspringwillbecarriers. DoyouthinkthatbreedersshouldmateaRRsheepwithacarrier?Whyorwhynot? Answerswillvary. 3. Youbuyahealthyramfromaneighboringfarm,andyoudonotknowhisgenotype.You matehimwithaSLScarrierandthelambisbornwithSLS. FillinthePunnettSquarewiththegenotypeoftheramandhisoffspring. Ram __N___ __n___ N NN Nn n Nn nn 3 Selectively Breeding Sheep (continued) 4. ArelativelysimplegenetictestisavailableforSLS.Accordingtotheinformationbelow,how muchwoulditcoststotestananimalforSLS?Ifyouhavealargeflockandalimitedbudget, whichsheep(ramsorewes)doyouthinkyoushouldselectfortestingandwhy? Thecostofatestis$20.Testingramsshouldbetestedbecausetheywillbematedwith multipleewesandpasstheirgenesofftomoreoffspringthanasingleewe.Thisisamore costeffectivestrategy. CostsassociatedwithgenetictestsavailablefromUniversityofCaliforniaDavisVeterinaryGeneticsLaboratory. AgelelectrophoresisshowingDNAbands forhomozygousNormal(NN),heterozygous carriers(Nn),andhomozygousSLS(nn) sheep. 4
