Do spouses begin to share genes over time?
Microchimerism (Mc) is an interesting concept, and


  refers to the harboring of a small number of cells (or DNA) that originated in a different individual. Naturally acquired Mc derives primarily from maternal cells in her progeny, or cells of fetal origin in women.


In women, it has nothing to do with transfer during/after sex but rather is due to the presence of the developing fetus.  There is definite long-term persistence of microchimerism, although not much is yet known about its effects.  Here is a nice and free review from 2010 dealing with the subject.  Most if not all of the effects have to do with immune function, in particular autoimmunity.  It is definitely not a mechanism by which couples begin to look similar.  That is social, in particular a result of living in the same environment with similar activities and tastes.  Male contribution to cellular content in the embryo is almost nil, as sperm die and the transcript count in the successful sperm is puny compared to the egg.  Most RNA content in the embryo is maternal until it switches to embryo.