Are there any rules for type conversion between C# generics?

I'm having an interface IJob from which all Job classes inherits and I have generic repo class which will process all kind of IJob's.

The problem im facing is im not able to able convert Repository<Job1> to Repository<IJob> even though Job1 is a type of IJob.

Code

internal class Program
{
    public interface IJob { }
    public class Job1 : IJob { }
    public class Job2 : IJob { }

    public class Repository<TJob>
        where TJob : IJob
    {
        public List<TJob> GetJobs()
        {
            return new List<TJob>();
        }
    }

    private static void Main(string[] args)
    {
        IJob iJob = new Job1(); // Valid
        Repository<IJob> repo = new Repository<Job1>(); // Not Valid
    }
}

Can someone let me know why this wont be possible in C# and are there any other rules type conversion in C# generics?