How to pass specific value to the converter parameter?

Try using x:Static markup extension:

<RadioButton 
        Content="Female" 
        IsChecked="{Binding Path=Gender, 
                    Converter={StaticResource genderConverter}, 
                    ConverterParameter={x:Static model:GenderType.Female}}"/>

OR, you could just pass a string and use Enum.Parse to convert that string to the enum type in the converter:

<RadioButton 
        Content="Female" 
        IsChecked="{Binding Path=Gender, 
                    Converter={StaticResource genderConverter}, 
                    ConverterParameter=Female}"/>

-

GenderType gender = (GenderType)Enum.Parse(typeof(GenderType), parameter.ToString());

Since you're creating your own converter why don't you just send a nullable bool as the converter parameter?

so for male,female,not specified send true,false,null.

If you don't want to do that you will have to reference your namespace in the beginning like this:

xmlns:myNamespace="clr-namespace:MyNamespace"

and then

<RadioButton 
    Content="Male" 
    IsChecked="{Binding Path=Gender, 
                Converter={StaticResource genderConverter}, 
                ConverterParameter=x:Static myNamespace:Person.GenderType.Male}"/>

for your radiobuttons.