Gross Motor Imitation

I am part of a birth board in on that board as our children come due for their check-ups people tend to post stats and ask questions after the visit with their pediatrician.
Because our children are coming into their 9 month check there have been all sorts of questions about shots, blood tests and interestingly enough whether or not the child claps in response to you clapping or waves hello or goodbye.
When I first started reading this my child didn’t do any of these things, so I of course began to wonder what the significance of these actions was.
In random conversation I mentioned it to my sister who works with children on the autistic spectrum.  She immediate said “oh yeah, gross motor imitation, he should be doing that right about now”. 
My response “he doesn’t”. 
“he will, don’t worry, he’s doing other things that wouldn’t make me nervous.”
So of course, then I was nervous.
I looked into it because I think as a parent autism is a scary thing.  It’s also not one of those things that you know about right away so my perfectly happy perfect boy could be fine, until he’s 9 months old and then everyone realizes that he doesn’t physically imitate actions. 
The reason that is a red flag is because children with autism have a difficult time understanding body language.  So if my son never learns to clap in response to me clapping then he most likely will not learn that my hands on my hips and a scowl on my face means I’m not happy.  Which means he’ll probably end up a genious like the character Sheldon on The Big Bang Theory, but he’ll never have a girlfriend.
It’s a scary concept and one that would be difficult to have to have to deal with.
Gross Motor Imitation is ond of those things that  had never heard of and didn’t even know to keep an eye out for.  But it is one of those things that is important so I put it out here so people know about it.
I will say my son has since started clapping in response to my husband and I clapping.  But that I think was in response to me all of a sudden realizing that we didn’t necessary do anything like that to help him.
We don’t typically wave goodbye or hello to him, we didn’t put in any effort to clap for him and to get him to clap in response to us.