The Bitcoin Dominance Index measures Bitcoin’s Market Cap/ Total Market Cap of All Cryptocurrencies. While the overall market has been in retracement for about a month, bitcoin dominance has regained some ground.
This type of action is expected. The liquidity profile is far lower in altcoins than it is in bitcoin on both the ask and the bid sides of the market. So during bull phases, prices of altcoins can significantly outperform, but on the way down they can severely underperform.