C# – How to “Fill” a GridViewColumn with ComboBox (WPF)

I am looking for a way to "completely fill" a GridViewColumn with a combo box. I am able to create a cell template with ComboBox and it is working fine. But the width and height of ComboBox is not aligned with the GridViewColumn.
Even if I try to set the same height/width GridViewColumn hides some part of the comboBox.

There must be some setting or style to instruct WPF to fill the ComboBox completely in the available space of GridViewColumn

This is my XAML.

<Window x:Class="WPFStarter.ComboInsideListView.ComboBoxInsideListViewUsingObject"
        x:Name="userControl"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="ComboBoxInsideListViewUsingObject" Height="300" Width="400">
    <Grid>
        <ListView x:Name="listView" ItemsSource="{Binding ElementName=userControl, 
            Path=DataContext.Items}" SelectedItem="{Binding ElementName=userControl, Path=DataContext.SelectedItem, Mode=TwoWay}">                   
            <ListView.View>
                <GridView>
                   <GridViewColumn Header="First Name"  DisplayMemberBinding="{Binding Path=First}"/>
                   <GridViewColumn Header="Gender">
                        <GridViewColumn.CellTemplate>
                            <DataTemplate>
                                <ComboBox x:Name="cmb_Gender" Width="75" SelectedValue="{Binding Path=Gender}"                    
                  ItemsSource="{Binding ElementName=userControl, Path=DataContext.Genders}" GotFocus="ComboBox_GotFocus"         />
                            </DataTemplate>
                        </GridViewColumn.CellTemplate>
                    </GridViewColumn>
                </GridView>

            </ListView.View>

        </ListView>
    </Grid>
</Window>