Duplications are also frequent in non-axenic wild types in the NC4 lineage. (a) NC4(L) chromosome (chr) 2, (b) NC4(B) chromosome 4, (c) NC4(S) chromosome 6. As well as the three strains shown, NC4(Wi) has a duplication overlapping that observed in NC4(S). It is not clear why duplications near the chromosome ends are especially frequent in these non-axenic lines, or indeed whether this is merely a sampling artifact. The parasexual segregant XP99 is not axenic and yet carries two duplications away from termini; however this strain inherited some of its chromosomes ultimately from Ax3 and we can be confident that one of these duplications occurred in that axenic ancestor.