It's the tufts that are the lethal gene, not the rumpless gene. The tufts gene is a dominant gene. One copy of that gene is not lethal and will show tufts but if the two genes at that gene pair are both tufts it will kill the chick before it hatches.
http://www.cashsblueeggs.com/araucanahistory.htm
So any bird that has tufts has one copy of the tufts gene and one copy that is not-tuft. If you breed two tufted chickens you get about 25% with two copies of the tuft gene that die before hatch, about 25% that have no tuft gene and are clean-faced, and about 50% that have one gene of each and have tufts.
Since it is a dominant gene if you breed a tufted bird to a clan-faced bird you get about 50% that have one copy of the tuft gene and have tufts. You get about 50% that are clean-faced. The gene does not pair up so it does not kill any in the shell.
Either way you get about 50% tufted birds. Since it is a dominant gene and will always show up if it is present it should be easy to manage.
http://www.cashsblueeggs.com/araucanahistory.htm
So any bird that has tufts has one copy of the tufts gene and one copy that is not-tuft. If you breed two tufted chickens you get about 25% with two copies of the tuft gene that die before hatch, about 25% that have no tuft gene and are clean-faced, and about 50% that have one gene of each and have tufts.
Since it is a dominant gene if you breed a tufted bird to a clan-faced bird you get about 50% that have one copy of the tuft gene and have tufts. You get about 50% that are clean-faced. The gene does not pair up so it does not kill any in the shell.
Either way you get about 50% tufted birds. Since it is a dominant gene and will always show up if it is present it should be easy to manage.