Yeah, I looked at pic of the G2 and didn't spot a TB2 connector but there is USB-C present. TB2 predates USB-C by year or two. And the G2 specs are vague, they just say there is TB-connector, not specifying the type. That is why I asked the questions above.Edit: had another look at the G2 and it uses TB3 (USB-C) which means that an adapter with female ports on both sides would be required but I can't find any.
And no, you don't need a female-female adapter. You would need the Apple TB3 to TB2 adapter which has a male USB-C and female TB2. The USB-C plugs into the TB3 dock -connector and a TB2 cable to the other end. But, the adapter costs more than the G2 - or the Mac compatible Elgato TB2 dock which I have mentioned now many times.
And the G2 only has 1 TB-connector so you can only connect it to a computer with it. You cannot plug a TB hard drive etc. into it. Docks with 2 TB-connectors allow that too. For example an external TB NVMe -drive would really fly through it. In DCBassmans case the 21.5" iMac only has 1 TB2-connector so no way to connect any TB-devices to the machine after using a G2 dock. 27" 2011 iMacs have 2 connectors.
Ps. one good use for the Apples bidirectional adapter would possibly be connecting an TB3 eGPU case to a TB2 equipped Mac. Most eGPUs are TB3 so they are much easier and cheaper to find than long obsolete TB2 eGPU cases. And obviously one could use a TB3 case also with newer Intel Macs.