@lazy_property<EOL><INDENT>def uca(self):<DEDENT>
return self._calculate_uca()<EOL>
Calculates the unmutated common ancestor (UCA) of the lineage.

The UCA is computed by using the germline V(D)J genes as well
as the N-addition regions of the least mutated sequence.

If both heavy and light chains exist in the lineage, the UCA
will be computed for both chains. If not, the UCA will only
be computed on the chains that exist in the lineage.

Returns
-------
A VaxTools Pair object containing the UCA.