Selecting Multiple Checkboxes On Single Click

I know how to do a select/deselect all function. Where I'm having issues is with a select some function. I am querying a database to come up with a list of companies. I then query the database to come up with individual names/email addresses associated with each company. (Individuals can appear under under multiple companies, and I need this to continue.) The checkbox name must remain the same from individual to individual.

What I want to happen: When I click on a name that appears multiple times, I want all related checkboxes to then be checked; also, if I uncheck one, all should then uncheck.
What I've been trying: Each record for John Doe has the same id name (not a must, but I thought this would make it easier. Though I don't think it is necessary, I am including a snippet below:

PHP Code:
<form name=form3>
<tr><td colspan=6>--Company A--</td>
</tr><tr>
<td width='3%'><input type=checkbox name=contact_sel id='contact206' value='jane.doe@company.com'></td>
<td width='30%'>Doe, Jane</td>
<td colspan=4> </td>
</tr><tr>
<td colspan=6>--Company B--</td>
</tr><tr>
<td width='3%'><input type=checkbox name=contact_sel id='contact118' value='john.doe@company.com'></td>
<td width='30%'>Doe, John</td>
<td width='3%'><input type=checkbox name=contact_sel id='contact33' value='mike.jones@company.com'></td>
<td width='30%'>Jones, Mike</td>
<td colspan=2> </td>
</tr><tr>
<td colspan=6>--Company C--</td>
</tr><tr>
<td width='3%'><input type=checkbox name=contact_sel id='contact118' value='john.doe@company.com'></td>
<td width='30%'>Doe, John</td>
<td width='3%'><input type=checkbox name=contact_sel id='contact206' value='jane.doe@company.com'></td>
<td width='30%'>Doe, Jane</td>
<td colspan=2> </td>
</tr></form>

Again, if I select/deselect someone from any Company, I want all of their related check boxes to follow suit. If there is a better use of id records, I'm all for it.