The only relationship I see between the two is the ideology behind Blockchain! But more to it is the fact that $Bitcoin being a pioneer is the word "Blockchain" itself there is no where you hear "Blockchain" that $Bitcoin isn't mentioned! Even when you talk about other coins, you can't help chipping in $Bitcoin at some point! Bitcoin detects the pace of the market for altcoins, where $Bitcoin suffers demeaning criticism, altcoins aren't left out because the parent technology "Blockchain" is a common idea that both $Bitcoin and Altcoins share!
Its a given thing specially because the codes are opensource. But in relation to its prices, I think its the traders that give gives significance to each. When tokens are dumped in exchange of BTC, literally means the demand of BTC foes up while price of that token goes down. Same thing when we do it with USDT which was very recent.
