Board Thread:Warhammer 40k General Discussion/@comment-4851119-20140118095944/@comment-24944355-20141220211103

You're overlooking something that being who said that any transplanted astartes passed on their gene seed? What is likely is that the surviving marines of the fallen legion would have been absorbed into the Ultramarines but banned from passing their gene seed on to create more astartes. As each year passed there would have been fewer until by the time of the heresy there would not have been many survivors of the fallen legion remaining. Also having that many extra marines added to there line of battle would have reduced the number of Guillimans astartes who died in battle which would have helped keep his numbers high as seen at the time of the heresy.