Yes. In fact, they're now one airline.  Alaska Airlines bought Virgin America in 2016 and the two airlines are now fully integrated. That means that if you have an Alaska Airlines Mileage Plan account, you can earn and redeem miles on Virgin Atlantic flights. Similarly, if you have a Virgin Atlantic Flying Club account, you can earn and redeem miles on Alaska Airlines flights. So whether you're flying across the pond or across the country, you can do so with just one loyalty program.