Difference between maternal inheritance and maternal effect

 Maternally inherited genes are genes in the genome of the child which have come from mother. These genes necessarily must be in the genome of the child in order to have some effect. 

Maternal effect genes, however, are genes in the mother's genome which have an affect on the child while he/she is in the uterus. Maternal effect genes do not have to be inherited by the fetus in order to affect the fetus. Basically, maternal effect genes are transcribed in the mother to produce mRNA.