The banks base these lending rates on their cost of funding, along with a risk premium to compensate them for the riskiness of the loan being made; that is, how likely the mortgage will be repaid. In addition, there is a mark-up to generate a rate of return for bank shareholders. So the cash rate has a large influence on lending rates.
But there are other factors such as credit risk premia, competitive pressures in the deposit market, as well as changes in the mix of funding banks use which mean that the relationship between the cash rate and lending rates may not always be one for one.