Material Select not woking

<div class="md-form form-sm">
    <i class="fa fa-venus-mars prefix"></i>
    <mdb-ng-select name="sexo" [options]="genderOptions" id="gender" placeholder="Selecciona el sexo" [(ngModel)]="patient.sexo" ></mdb-ng-select>
    <label>Sexo</label>
    <!--<small class="text-danger">error</small>-->
</div>

ngOnInit() {
    this.genderOptions = [
        { value: 'HOMBRE', label: 'Hombre' },
        { value: 'MUJER', label: 'Mujer' }
    ];
}

<mdb-ng-select _ngcontent-c2="" id="gender" name="sexo" placeholder="Selecciona el sexo" ng-reflect-options="[object Object],[object Object" ng-reflect-placeholder="Selecciona el sexo" ng-reflect-name="sexo" ng-reflect-model="MUJER" class="ng-untouched ng-valid ng-dirty"><!--bindings={
"ng-reflect-ng-if": "false"
}-->
<div class="below" ng-reflect-ng-class="[object Object]" tabindex="0">

<!--bindings={
"ng-reflect-ng-if": "true"
}--><div class="single">
<!--bindings={
"ng-reflect-ng-if": "true"
}--><div class="value">
Mujer
</div>
<!--bindings={
"ng-reflect-ng-if": "false"
}-->
<!--bindings={
"ng-reflect-ng-if": "false"
}-->
<!--bindings={
"ng-reflect-ng-if": "false"
}-->
<!--bindings={
"ng-reflect-ng-if": "true"
}--><div class="toggle">
▼
</div>
</div>

<!--bindings={
"ng-reflect-ng-if": "false"
}-->

</div>
<!--bindings={
"ng-reflect-ng-if": "false"
}--></mdb-ng-select>