Bitcoins price is very important to altcoins, because it can affect the price markets of altcoins. The main reason for these relations is, bitcoin has its own market. You can buy alts using bitcoin that is why there are effects on alts price when BTC price moved. I dont know what ratio you are talking about, but determining the BtC conversion to USD doesnt effect alts as well as BTC as far as i know, and the same, I think the price of altcoins is completely dependent on the price of bitcoin. The more expensive the main coin the more expensive and altcoins. If the price of bitcoin falls then the price of all cryptocurrencies falls too. I think that it is possible to navigate using a pair of bitcoin dollar.