If continuously bred back to patts the subsequent generations would be like this (P being patts, and L being lakies)
1st gen is 1/2P, 1/2L or 50%P, 50%L
2nd gen is 3/4P, 1/4L or 75%P, 25%L
3rd gen is 7/8P, 1/8L or 87.5%P, 12.5%L
4th gen is 15/16P, 1/16L or 93.75%P, 6.25%L
5th gen is 31/32P, 1/32L or 96.875%P, 3.125%L
6th gen is 63/64P, 1/64L or 98.4375%P, 1.5625%L
edited to add percentages