If you are a member of a species with 3 females to every 1 male, that means the average male of your species has 3 times as many offspring as the average female.
Under those circumstances, if you have a mutation that causes you to produce all male offspring, you will have many more grandchildren than average.
This pressure will always favor producing whatever sex is in short supply, pushing sex ratios to 50%.
Under those circumstances, if you have a mutation that causes you to produce all male offspring, you will have many more grandchildren than average.
This pressure will always favor producing whatever sex is in short supply, pushing sex ratios to 50%.