TikZ Picture of Poisson, Gamma, Dirichlet, and Multinomial distributions

GamDirPoiMul.tex

\documentclass[tikz,border=10pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{positioning, arrows.meta}

\begin{document}
\begin{tikzpicture}[
  node distance=30mm,
  box/.style={draw, rounded corners, align=center, inner sep=6pt, minimum height=5em ,minimum width=7em},
  arrow/.style={->, thick}
]

% 上段
\node[box] (P) {{\footnotesize product of}\\Poisson};
\node[box, right=of P] (G) {{\footnotesize product of}\\Gamma};

\draw[arrow, <-] (P) -- node[above]{Conjugate} (G);

% 下段
\node[box, below=of P] (M) {Multinoimial\\\\};
\node[box, below=of G] (D) {Dirichlet\\\\};

\node[box, fill = white, yshift = 1.5em, minimum height=1em, minimum width=5em] at (M.south) {Binomial};
\node[box, fill = white, yshift = 1.5em, minimum height=1em, minimum width=5em] at (D.south) {Beta};

\draw[arrow, dashed] (P) -- node[left, rotate=90, yshift = 1em, xshift =4em]{cond. on total} (M);
\draw[arrow, dashed] (G) -- node[left, rotate=90, yshift = 1em, xshift =4em]{cond. on total}(D);

\draw[arrow, <-] (M) -- node[above]{Conjugate} (D);

\end{tikzpicture}
\end{document}