Vicki, you are exactly right about the cross breeding of American with Asian. They keep doing the crosses until it is 99% American and 1% Asian.
If you are interested in growing citrus from seed I have a technique the helps in germination. I learned it from an asian kid on youtube. In the pics below, I am preparing pummelo seeds for planting. Pummelo is like a huge grapefruit, but it is sweeter. What you do is you peel off the outer leathery covering and remove the seeds and then plant them. I have been able to get the pummelo to grow but they do not survive winter outside, even in Georgia. This technique works on orange seed and should work on lemon, lime, and grapefruit.