XeLaTeX with ucharclasses and Greek Support

Try the following code:

\documentclass[12pt,a4paper]{article}
\usepackage[Latin,Greek]{ucharclasses}
\usepackage{fontspec}
\newfontfamily\mynormal{Palatino Linotype}
\setDefaultTransitions{\mynormal}{}
\newfontfamily\mygreek{Junicode} 
\setTransitionsForGreek{\mygreek}{}
\usepackage{lipsum}
\begin{document}
    \lipsum[1]
    Πέτρος ἀπόστολος Ἰησοῦ Χριστοῦ ἐκλεκτοῖς παρεπιδήμοις διασπορᾶς Πόντου, Γαλατίας, Καππαδοκίας, Ἀσίας καὶ Βιθυνίας
\end{document}