convert a class object into another class object and then combine

Say that I have two models/classes.

public class Male
{
    public int RunNumber { get; set; }
    public string Notes { get; set; }
    public DateTime thing {get ; set;}
}

public class Female
{
    public int StopNumber { get; set; }
    public string Notes { get; set; }
    public DateTime? thing {get;set;}
}

I want a List<People> by combining List<Male> and List<Female>. Every time I look at LINQ, my brain doesn’t cooperate with me. I think it’s concat I’m after.

convert a class object into another class object and then combine