In my career, I've had the opportunity to be on many different teams across many different industries, and I've found that my favorite teams had a few traits in common where the teams that I disliked the most also had similar traits in common.
On the teams that excelled, there was a common theme, community. The alpha coder (or coders in some situations), in the group didn't show dominance over the group, but instead were stewards of knowledge and understanding.
Everyone has worked with the coder whose only joy in life seems to be holding all the information and never sharing it with anyone else. They will make others on the team feel stupid while elevating themselves at the other persons expense. This is toxic in a team.
The best teams will have leaders at every level whose purpose is to try and equalize a teams knowledge through collaboration and transfer. Say for example you have a C# developer who is really good in the business layer and you have another developer who is really good in the persistence layer. Pairing those two together on a series of tasks will help each see the pieces of the other which may not be as sharpened in their own toolset and will give them the opportunity in a productive, real time way, to enhance themselves and still do their job.
If you can build a team where every member in the group can do the job of every other member of the group, then you have a synergistic group which can do truly amazing things.
On the other side of it, if you have a team where there are alpha's who keep their skills and information hidden away for their own benefit you will create a team where a few highly skilled individuals create failure points in your IT organization and who can also leverage that power in future negotiations around salary and promotions, while leaving the rest of the team weakened, and often seeking other opportunities.
A team must strive to operate as a single entity with empowered, antonymous individuals who understand the need for serving the group to elevate the group. This is a rare thing to find, a hard thing to build, but when it aligns correctly, the result is not only beautiful, but inspiring.