documentclass[10pt,english,xcolor={usenames,dvipsnames}]{beamer}
begin{document}


begin{frame}[label=id1]
frametitle{A non-identification result}
begin{itemize}
item<1-> 1
begin{itemize}
item<2->   The equation is
    only<2>{begin{equation*}
    x = y
        end{equation*}}
    only<3>{begin{equation*}x = z
    end{equation*}}
    onslide<4->{begin{equation*}x=textcolor{red}{z}
    end{equation*}}
    item<4-> yet \
     onslide<5->...  $x = u$
end{itemize}
item<6-> There is a jump at 2
item<7-> and at 4
end{itemize}
end{frame}
end{document}