You have to distinguish between the imprint that your parents
put onto your own chromosomes, and the imprint that you will impose
upon your children. To make sure that the imprint that your parents
gave your chromosomes is maintained for each cell in your body, you
need the maintenance methyl transferase. Each time one of your cell
is diving, it had to duplicate its DNA beforehand. And each time
your DNA is duplicated, the fully methylated sites are
hemi-methylated at first. The maintenance methyl transferase
converts these hemi-methylated sites into fully methylated sites to
make sure sure that the imprint your mother put on the chromosomes
that she gave to you are still in the female imprinted, maternal
state.
However, once you have children, you will put a male imprint on the
chromosomes that you are passing on, even on the chromosomes that
you yourself received from your mother. Therefore, the parental
imprint has to be removed when you are producing sperm cells, and
the chromosomes are now imprinted according to your male sex. The
same is true for your wife. Half of the chromosomes in her body are
carrying the male imprint from her father. She is maintaining this
pattern for all the (somatic) cells in her body except for the germ
cells that she is producing. She is removing all the parental
imprints on the chromosomes in the egg cells that she is producing,
and she is putting her own, female imprint on the chromosomes that
she is passing on to your children.
