How to make a 5 checkbox to be marked with values from databases

i want to make a form with 5 checkbox that will be retrieved from my table genres that contain(ID, name) of books (from database)-this works, and i want to mark old genres from my table book_genre, this contain(ID,ID_book, ID_genre) and then to make an update with new genres - this did not work.

I did this:

                    <div>
                        <input type="checkbox" name="ID_gen<? echo $id=$row_genre_new['ID']; ?>" 
                                value="1" <? if($row_genre_old['ID_genre'] ) echo 'checked="checked"';  ?> />
                        <? echo $row_genre_new['name']; ?>
                    </div>  

                            <!--
                            <div>
                                <input type="checkbox" name="ID_gen<? echo $id=$row_genre_old['ID']; ?>" 
                                        value="1" checked="checked" />
                                    <? echo $row_genre_old['name']; ?>
                            </div>
                            -->

             <? } ?>