Major scales?

I'm a piano student and I was working in my music theory book on the section about major scales. I know that a major scale is comprised of two Tetrachords and that a Tetrachord has a pattern of whole step, whole step, half step. I was reading about the G major scale which I know has an F# in the key signature. It said that if the F# was an F natural then the second Tetrachord of the scale would have a pattern of whole step, half step, whole step instead of whole step, whole step, half step. This makes sense but in the G major scale after the half step of B-C it goes C-D, D-E, E-F#, and F#-G. Wouldn't that make the pattern whole step, whole step, whole step, half step?