First off, a short and sweet, 'clear' answer:
Theoretically, Tsunade and Yamato should both be capable off passing it down through breeding, though Yamato has more potential, since his genes are essentially the same.
Now, more details:
1. Tsunade is 2 generations off Hashirama, and although it's likely that she no longer posses 'all' the genes to pass it on, there's a chance she could.
2. Yamato is a 'genetically engineered' mutant. All his cells were supposedly infused with Hashirama's RNA, which is why all his peers died. His DNA now has the mokuton genes, and his RNA will have them as well. If sperm from him with RNA that has all necessary mokuton genes, succesfully fertilizes an egg (even from a fodder like Sakura), and a baby is successfully born, that baby has high potential.
See, having the DNA doesn't mean the genes get passed on either, as most abilities are based on multiple genes that all need to be included in one full RNA strand.
Now for even more info:
Mokuton depends on genes, but also on transmigration. To-date, all mokuton users apart from Hashirama himself have done so through his very DNA. No other senju has ever been born with it, before or after Hashirama. And what else makes Hashirama unique? corrent - he's Ashura's transmigrant.
Now, Yamato's use of mokuton may mean that it is possible without transmigration, but it may also not mean so, as Yamato may simply have received some of the transmigration material, be it DNA, or otherwise.