Because fraternal, or dizygotic, twins are 2 separate fertilized eggs, they usually develop 2 separate amniotic sacs, placentas, ...TurnonmoreaccessiblemodeTurnoffmoreaccessiblemodeSkipRibbonCommandsSkiptomaincontentTurnoffAnimationsTurnonAnimationsOurSponsorsLogin|RegisterMenuLogin|RegisterHomeOurSponsorsAges&StagesAges&StagesAgesandStagesPrenatalDecisionstoMakeDeliveryandBeyondBaby(0-12mos.)FormulaFeedingToddler1-3yrs.NutritionPreschool3-5yrsGradeSchool5-12yrs.Teen12-18yrs.YoungAdult18-21yrs.HealthyLivingHealthyLivingHealthyLivingNutritionFitnessSportsOralHealthEmotionalWellnessGrowingHealthySleepSafety&PreventionSafety&PreventionSafetyandPreventionImmunizationsAtHomeAtPlayOnTheGoAllAroundFamilyLifeFamilyLifeFamilyLifeMedicalHomeFamilyDynamicsMediaWork&PlayGettingInvolvedinYourCommunityHealthIssuesHealthIssuesHealthIssuesConditionsInjuries&EmergenciesVaccinePreventableDiseasesNewsNewsTips&ToolsTips&ToolsTipsandToolsAskThePediatricianFindaPediatricianNewslettersSymptomCheckerWebinarsHealthyChildrenMagazineHealthyChildrenTextingProgramOurMissionOurMissionOurMissionAAPinActionMedicalEditor&ContributorsSponsorsSponsorshipOpportunitiesSpreadtheWordShopAAPFindaPediatrician FamilyLifeMedicalHomeFamilyDynamicsAdoption&FosterCareCommunication&DisciplineTypesofFamiliesMediaWork&PlayGettingInvolvedinYourCommunityInThisSectionHealthyChildren>FamilyLife>FamilyDynamics>TheDifferenceBetweenIdenticalandFraternalTwinsFamilyLifeListenEspañolTextSizeTheDifferenceBetweenIdenticalandFraternalTwins ‭(Hidden)‬ContentEditorPageContentArticleBodyBecausefraternal,ordizygotic,twinsare2separatefertilizedeggs,theyusuallydevelop2separateamnioticsacs,placentas,andsupportingstructures.Identical,ormonozygotic,twinsmayormaynotsharethesameamnioticsac,dependingonhowearlythesinglefertilizedeggdividesinto2.Iftwinsareaboyandagirl,clearlytheyarefraternaltwins,astheydonothavethesameDNA.AboyhasXYchromosomesandagirlhasXXchromosomes.Girl-boytwinsoccurwhenoneXeggisfertilizedwithanXsperm,andaYspermfertilizest