Default value in an asp.net mvc view model

Set this in the constructor:

public class SearchModel
{
    public bool IsMale { get; set; }
    public bool IsFemale { get; set; }

    public SearchModel()
    { 
        IsMale = true;
        IsFemale = true;
    }
}

Then pass it to the view in your GET action:

[HttpGet]
public ActionResult Search()
{
    return new View(new SearchModel());
}