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ANSC 1000 Test 2 Lecture 6-7

by: Brianna Notetaker

ANSC 1000 Test 2 Lecture 6-7 ANSC 1000

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Brianna Notetaker

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These notes cover the remainder of the genetics portion of livestock production.
Introduction to Animal Sciences
Alese Grey Parks
Class Notes
ANSC, animal, Science
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This 13 page Class Notes was uploaded by Brianna Notetaker on Friday September 30, 2016. The Class Notes belongs to ANSC 1000 at Auburn University taught by Alese Grey Parks in Fall 2016. Since its upload, it has received 2 views.


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Date Created: 09/30/16
ANSC 1000Test 2 Lecture 6 Six Types of(Genetic) Mating  Withthree kindsofindividuals(homozygousdominant,homozygous recessive,andheterozygous)andonepair ofgenes being considered,six types ofmatingare possible  Usinggenes designatedasB = black,andb = red in cattle,the six mating possibilitiesare: o BB X BB o BB X Bb o BB X bb o Bb X Bb o Bb X bb o bb Xbb HomozygousDominantx HomozygousDominant(BB x BB)  Onlyproduceonekind ofgene, B 
  Therefore,the unionofthe gametes,from two homozygousdominant parentswillbe B X B 
  Resultingina BB offspring  Therefore,homozygousdominantparentsproducehomozygous dominantoffspring
 HomozygousDominantx Heterozygous(BB x Bb)  The genotypicratioof
theoffspringwillbe 1:1 homozygousdominantBb to heterozygous  Allare black HomozygousDominantx HomozygousRecessive(BB x bb)  Alloffspringwill be heterozygous(Bb)  Alloffspringwill be black Heterozygousx Heterozygous(Bb x Bb)  Each parentwillproduceeithera B or b 
  Four chances,withthree outcomes
  The genotypicratiois 1:2:1 (25% BB,50% Bb,and25% bb) 
 2  Andthe appearanceofthe offspringwill be 3dominant:1recessive 
  This3:1 ratiois the phenotypicratio Heterozygousx HomozygousRecessive(Bb x bb)  1 heterozygous:1homozygousrecessive  Genotypicsameas phenotypicratio HomozygousRecessivex HomozygousRecessive(bb x bb)  Alloffspringwill be homozygousrecessive  Alloffspringwill be red 3 MultipleGenePairs  Assumethere are two gene pairsto be considered,each independently affectinga particulartrait
  One determinescoat color(B = black,b = red) 
  The otherdeterminespolledorhorned(P= polled,p= horned) 
  If a bullisheterozygousfor bothtraits,(BbPp)andmatesheterozygous cows, we can calculatetheexpectedphenotypicandgenotypicratios  CrossingBb X Bb = 3:1 blackto red ������Pp X Pp gives 3:1 polledtohorned  CombineBbPpX BbPp:  Get 9blackpolled,3blackhorned,3red polled,and1red horned BbPp x BbPp (9:3:3:1) 4 Genotypes&Phenotypes(BbPp x BbPb) Gene Interactions  Withanothergene inthe same chromosome o Linear interaction
  Withits correspondinggenein a homologouschromosome o Allelicinteraction
  Or withgenes innon-homologouschromosomes o Epistaticinteraction
  Environmentalfactorsmayinteractwithgenes o Internally‐Ex:hormones o Externally‐ Ex:nutrition,temp,amountoflight  Linear interactionsareknowntoexist inlower animals(Drosophilafruit fly),but havenotbeen demonstratedinfarmanimals AllelicInteractions  Each gene occupyingthe samelocus onhomologouschromosomesmay influencethetrait individually o Effect dependsondominance 5  Allelicinteractionsmayalsobe calleddominanceinteractions  Whenunlikegenes occupycorrespondingloci,completedominancemay exist o Only the dominantgeneisexpressed  Ex:polled(hornless)conditionincattle o Phenotypically,theheterozygousanimalisindistinguishablefrom the homozygousdominant(bothpolled) IncompleteDominance  There mayalsobe a lackofdominanceinwhich the heterozygousanimal shows a differentphenotypethaneitherhomozygousanimal(dominant or recessive); intermediateresult
  A good exampleissheep ear length o LL havelongears,and llare earless o The Ll heterozygoussheephave shortears,beingintermediate  Known as incompletedominance
 Codominance  In some cases,neitherallelemaybe dominantovertheother  Bothcharacteristicsare expressedatthe same time  Ex:Red vs. Whitehaircolor incattle o RR = red o WW = white o RW = roan(mixtureofred andwhite hairs) 6 ANSC 1000Test 2 Lecture 7 AdditiveGeneAction  Additivegeneactionoccurs wheneach gene hasan expressed phenotypiceffect (AVG,Milkproduction,etc.)  EXAMPLE: o ifD gene and d gene influencerateof gain(D = 0.1lb/dand d = 0.05 lb/d) o DD (homozygousdominant)increasesgainby0.2 o Dd (heterozygous)increasesgain by0.15 o dd (homozygousrecessive)increasesgain by0.10 lb/d  Example: o There is evidencethatmanygenes influencemanyproduction parameters,likerate ofgain o The D andd gene as before alsomayworkwith the N andn gene in the same respect o D = 0.1 lb/dandd = 0.05 lb/d o N = 0.1 lb/dandn = 0.05 lb/d 7 AllelicInteractions  Overdominanceisa conditionwherethe heterozygousanimalsare superiortoeitherof thehomozygousconditions  Showbettervigor, more milk,better fertility  Heterozygotes ofbreedcrosses are more vigorousthanstraight‐bred parents o Heterosis  Thisgreater vigor or productivityofcrossbredsis alsosaidto be an expressionofhybridvigor. AllelicInteractions–Review  Completedominance–Dominantallelefullymasksexpressionof recessiveallele  Incompletedominance–Heterozygote expressionisintermediate betweendominantandrecessive  Codominance– Heterozygote expressestraitsofbothdominantand recessivealleles  Overdominance– Heterozygousis superiortoeither homozygous phenotype 8 EpistaticInteraction  Whena gene or gene pairalters or masksthe expressionofgenes on anotherchromosome,thisisepistaticinteraction  In otherwords,a gene thatinteractswith a gene thatis not allelic(same locus,homologouschromosome)toit is saidtobe epistatic
  Example:coat colorin horses o Extensiongenedetermines2basiccoatcolors as eitherblackor chestnut,anythingelseexhibitedis a variationoneitherblackor red (chestnut)  Recessivegene, e, produceschestnut  EE andEe are black o Agoutigene determineswhetherEE or Ee foalwill be bayor solid black (Agoutihasno effect onred colors,restrictsthe blackgene)  Recessivegene, a,producessolidblack  AA andAa are bay o Andmanyothermodifyinggenes!  Epistasiscanresultfrom a dominantorrecessivegene or combinationof both  AnotherEXAMPLE: o WhiteRock chickens  C = color,c = albino  W = color,and w= white o Homozygouscc preventsW from showing andww preventsCC from showing InteractionsBetweenGenes& Environment  Genesinteractwith bothinternalandexternalenvironments o Externalinclude:temperature,light,altitude,humidity,disease, andfeed supply
  Some breeds(Brahman)can withstandhightemperaturesbetterthan others
  Other breeds(Scotch Highland)can withstandtheextremecoldbetter thanothers
 9  One ofthe most important(ifnotthe mostimportant)isfeed supply (nutrition)  Some breedscan survivewhen feed is inshort supplyforlongperiodsof time, andthey mayeat justaboutanythingtheycan (nutritional deficiency) o Ex:“easy keepers”– takes fewer caloriesto meet nutritionalneeds  Other breedsselect onlypalatablefeed,andthereforehavepoor productionwhenfeedis in shortsupply  Allelic,epistatic,andenvironmentalinteractionsallinfluencethegenetic improvementthatcanbe made throughselection 
  Whenthe environmenthasalarge effect on productiontraits,genetic improvementislow
  EXAMPLE: If animalsina populationaremaintainedatdifferent nutritionallevels,thosethatareconsumingbetterdietsperform better o Much ofthe growth difference is dueto the environmentalfactor ofnutrition,notgenetics o The producerhastwo alternatives:  Standardizetheenvironmentsothatit causes lessvariation  Maximizethe expressionoftheproductiontraitbyimproving the environment Biotechnology  Use oflivingorganismstoimprove,modify,or produceindustrially importantproducts o Microorganismsusedinproductionoffoodssuch as fermented dairyproducts  Geneticengineering o Removing,modifying,addinggenes to DNA 
 o Research allowsusto identifyandmanipulateDNAatmolecular& cell level 
  Superovulation o Hormonalmanipulationtoproducegreaterthannormalnumberof eggs 10  Breed donor& flushuterus o Transferto recipientfemale  Reverse ofA.I.  Sexingofsemen – purchasingsementhat hasalreadyhadthe sex chromosomeidentifiedthatisbeingcarried,reducesfertility  Embryosplitting(cloning)– Dollythesheep was clonedfrom an adult cell,she startedwithDNA thatwas aged;Horse clonedtohavehis geneticmaterialavailableforbreeding  Embryotransfer – donortorecipient– embryotaken from onefemale andplacedin another  Geneticengineeringaltershereditarytraits– make animalsmore productiveandresistanttodiseases  RankedbyAAASas 1of4 majorscientificadvancementsin20th century among: o Unlockingthe atom o Escapingearth’sgravity o Computerrevolution
  $BILLION industry o Career opportunity!!
 Genes& Biotechnology  Canpotentiallyremovedisorders/defectsfromDNA  Enzymes are “geneticscissors” o CutDNA at designatedplaces o Reconstructuniquecombinations  Inject genes from other animalsofsame or differentspecies o Mimics nature;Viruses o Performed in vitro(artificialenvironment) 11  Bovinesomatotropin–naturallyoccurringhormone thatincreasesmilkproduction  Cloningraisespractical,legal& ethicalquestions o Not likelyto gain widespreadutilization  Low efficiencyofgaininga pregnancy  Increasedbirthweights of clones  Costprohibitive  Transgenicpigs;genes from otherspecies o Heart healthyomega‐3fattyacids o Anatomic& physiologiccharacteristicsideal  Nuclear fusion o Unionofnucleifrom two sex cells 
 o Two eggs or two sperm can occur 
 o Outstandingmalesandfemalescan be unitedandtransferredto recipientfemale  Gene therapy
 o Insert genes intocell to treator cure disease
 12 o GeneticallyalteredWBCfor immunity FutureDirections?  Identificationofgenome offarm animals  Animalswithresistanceto specificdisease  Feedstuffswith vaccines againstdisease  Controlofparasitesbyalteringimmunity  GMO mayhelppreventhunger  Identifyingfoodcontaminants  “Smart” drugsdistinguishhealthyvs.cancer 13


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