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<!-- DFIN ActiveDisclosure(SM) XBRL Schema Document - http://www.dfinsolutions.com/ -->
<!-- Creation Date      : 2020-05-06T19:07:15.4867125+00:00 -->
<!-- Version            : 5.0.1.385 -->
<!-- Package ID         : 89bfca186a66422bbc4f18045dd9ef5c -->
<!-- Copyright (c) 2020 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
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  <xsd:element id="psnl_LineOfCreditFacilityExtendedMaturityDate" name="LineOfCreditFacilityExtendedMaturityDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_ClassOfWarrantOrRightTerm" name="ClassOfWarrantOrRightTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_EstimatedFairValueOfWarrants" name="EstimatedFairValueOfWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="psnl_PercentageOfPrepaymentFee" name="PercentageOfPrepaymentFee" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_PercentageOfPrinciplePaymentAmount" name="PercentageOfPrinciplePaymentAmount" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_CoLocatedDataCenterSpaceMember" name="CoLocatedDataCenterSpaceMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_LaboratoryAndOfficeSpaceLeaseMember" name="LaboratoryAndOfficeSpaceLeaseMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_LesseeOperatingLeaseExtensionTerm" name="LesseeOperatingLeaseExtensionTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_LeaseTermExtendedMonthAndYear" name="LeaseTermExtendedMonthAndYear" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_LeaseTermExtensionCommencementDate" name="LeaseTermExtensionCommencementDate" type="xbrli:dateItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_PercentageOfModifiedDataCenterSpace" name="PercentageOfModifiedDataCenterSpace" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_MinimumLeasePaymentsIncreasedForRemainderOfLeaseTerm" name="MinimumLeasePaymentsIncreasedForRemainderOfLeaseTerm" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="psnl_SeriesARedeemableConvertiblePreferredStockMember" name="SeriesARedeemableConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_SeriesBRedeemableConvertiblePreferredStockMember" name="SeriesBRedeemableConvertiblePreferredStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_NumberOfFractionalSharesIssued" name="NumberOfFractionalSharesIssued" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_NumberOfIssuedCommonSharesReducedUponConversion" name="NumberOfIssuedCommonSharesReducedUponConversion" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_ShareBasedCompensationByShareBasedPaymentAwardExercisePriceGrantedToPercentageOfStockholder" name="ShareBasedCompensationByShareBasedPaymentAwardExercisePriceGrantedToPercentageOfStockholder" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_ShareBasedCompensationByShareBasedPaymentAwardPercentageOfExercisePriceOfOptionsGranted" name="ShareBasedCompensationByShareBasedPaymentAwardPercentageOfExercisePriceOfOptionsGranted" type="num:percentItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_TwoThousandElevenEquityIncentivePlanMember" name="TwoThousandElevenEquityIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_IncentiveStockOptionsMember" name="IncentiveStockOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_OptionsGrantedAsMeritAwardsMember" name="OptionsGrantedAsMeritAwardsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_TwoThousandNineteenEmployeeStockPurchasePlanMember" name="TwoThousandNineteenEmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodButNotVested" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodButNotVested" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndEquityInstrumentsOtherThanOptionsGrantsInPeriodUnvestedAndUnexercisedButReservedSharesYetGranted" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsAndEquityInstrumentsOtherThanOptionsGrantsInPeriodUnvestedAndUnexercisedButReservedSharesYetGranted" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_TwoThousandNineteenPlanMember" name="TwoThousandNineteenPlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_TwoThousandElevenAndTwoThousandNineteenEquityIncentivePlanMember" name="TwoThousandElevenAndTwoThousandNineteenEquityIncentivePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesIncreaseInAvailableForGrant" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesIncreaseInAvailableForGrant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_ClosingPriceOfCommonStock" name="ClosingPriceOfCommonStock" type="num:perShareItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" />
  <xsd:element id="psnl_ConvertiblePreferredStockWarrantsLineItems" name="ConvertiblePreferredStockWarrantsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_ConvertiblePreferredStockWarrantsTable" name="ConvertiblePreferredStockWarrantsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_TermLoanMember" name="TermLoanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_AlternativeInvestmentTerm" name="AlternativeInvestmentTerm" type="xbrli:durationItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_EstimatedFairValueConvertiblePreferredStockWarrant" name="EstimatedFairValueConvertiblePreferredStockWarrant" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_FairValuesOfConvertiblePreferredStockWarrants" name="FairValuesOfConvertiblePreferredStockWarrants" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="psnl_ReclassificationOfOutstandingPreferredStockWarrantLiabilityToAdditionalPaidInCapitalFairValue" name="ReclassificationOfOutstandingPreferredStockWarrantLiabilityToAdditionalPaidInCapitalFairValue" type="xbrli:monetaryItemType" substitutionGroup="xbrli:item" xbrli:periodType="instant" nillable="true" abstract="false" xbrli:balance="credit" />
  <xsd:element id="psnl_CommonStockWarrantExercised" name="CommonStockWarrantExercised" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_CommonStockIssuedForExerciseOfWarrant" name="CommonStockIssuedForExerciseOfWarrant" type="xbrli:sharesItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="false" />
  <xsd:element id="psnl_CommonStockWarrantsLineItems" name="CommonStockWarrantsLineItems" type="xbrli:stringItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_CommonStockWarrantsTable" name="CommonStockWarrantsTable" type="xbrli:stringItemType" substitutionGroup="xbrldt:hypercubeItem" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_SeriesBPreferredStockWarrantMember" name="SeriesBPreferredStockWarrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_SeriesCPreferredStockWarrantMember" name="SeriesCPreferredStockWarrantMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_OptionsToPurchaseCommonStockMember" name="OptionsToPurchaseCommonStockMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_UnvestedRestrictedStockUnitsMember" name="UnvestedRestrictedStockUnitsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_EmployeeStockPurchasePlanMember" name="EmployeeStockPurchasePlanMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
  <xsd:element id="psnl_UnvestedEarlyExercisedCommonStockOptionsMember" name="UnvestedEarlyExercisedCommonStockOptionsMember" type="nonnum:domainItemType" substitutionGroup="xbrli:item" xbrli:periodType="duration" nillable="true" abstract="true" />
</xsd:schema>
