用于连接表的PHP到SQL复选框？

I have a junction table to link a many to many relationship between the table SERIES(PK series_id) and GENRE(PK genre_id). The form I have set up uses check boxes, like so:

<tr><td><input type="checkbox" name="genre" value="1" />Action </td>
<td><input type="checkbox" name="genre" value="2" />Adventure </td></tr>
<tr><td><input type="checkbox" name="genre" value="3" />Comedy</td>
<td><input type="checkbox" name="genre" value="4" />Coming of Age</td></tr>

The table in SQL appears like so, for example:

SERIES_ID    GENRE_ID
A0000        1  
A0000        2
B0000        2
B0000        6
C0000        1

The integers of genre_id reference the GENRE table where they are explained. For example, as you see above, 1 = Action.

So how would I go about making PHP that would allow me to insert into this junction table multiple rows with the same SERIES_ID and different GENRE_ID's. Like a user wants to submit a new series by the ID D0000 and it is both an action and adventure, so we would need to add these two rows with this form:

D0000     1
D0000     2

All the code I have been able to uncover regards counting the check boxes. I know that there is must be way but haven't been able to find it.