File:Transitions and transversions.svg

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\usepackage{chemfig,chemmacros}
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\begin{document}
\begin{tikzpicture}[>=stealth']
	\draw 
		node at (-2,2) (a) {\Large A}	node at (2,2) (g) {\Large G}
		node at (-2,-2) (c) {\Large C}	node at (2,-2) (t) {\Large T}
	;
	\draw [<->,fill=blue,draw=blue,ultra thick] (a) -- (g) node [pos=.5,blue,above] (t1) {\small Transitions};
	\node [above=of t1] {\small purines};
	\draw [<->,draw=blue,fill=blue,ultra thick] (c) -- (t) node [pos=.5,blue,below] (t2) {\small Transitions};
	\node [below=of t2] {\small pyrimidines};
	\draw [<->,fill=red,draw=red,ultra thick] (c) -- (g);
	\draw [<->,fill=red,draw=red,ultra thick] (a) -- (t);
	\draw [<->,fill=red,draw=red,ultra thick] (a) -- (c) node [pos=.5,red,left] {\small Transversions};
	\draw [<->,fill=red,draw=red,ultra thick] (g) -- (t) node [pos=.5,red,right] {\small Transversions};
	\node [above left=-10pt of a] {\chemname{
		\chemfig{*6(=N-*5(-N(-[6,.6,,,draw=none]H)-=N-)=-(-NH_2)=N-)}
		}{adenine}
	};
	\node [above right=-10pt of g] {\chemname{
		\chemfig{*6((-H_2N)=N-*5(-N(-[6,.6,,,draw=none]H)-=N-)=-(=O)=HN-[,,2])}
		}{guanine}
	};
	\node [below right=-10pt of t] {\chemname{
		\chemfig{*6(-N(-[6,.6,,,draw=none]H)-(=O)-NH-(=O)-(-)=)}
		}{thymine}
	};
	\node [below left=-10pt of c] {\chemname{
		\chemfig{*6(-N(-[6,.6,,,draw=none]H)-(=O)-N=(-NH_2)-=)}
		}{cytocine}
	};
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\end{document}