Another common use for a backcross is to combine two quantitative traits at a given ratio. For example, beef cattle hardy enough to survive the climate of North Australia are bred by crossing Australian cows with Brahma bulls from India. The F1 progeny, which share 50% of their genotype with either parent, are then backcrossed to the Australian parents to achieve a 75% expression of the Australian genotype and 25% expression of the Indian -- enough to give the F2 offspring resistance to north Australian conditions. This is a useful way to introduce a novel gene into a population while retaining most of the original population's genotype; the disadvantage is that excessive backcrosses can lead to inbreeding depression. Successive backcrosses can be performed with different combinations of males and females to achieve varying degrees of heterosis and relatedness (as in a three-breed cross or rotational cross).