I watched a show about 3 years ago on the overwhelming number of newborn babies in foster care in Russia. Even as newborns they suffered the consequences of separation and lack of human contact. This affects their personalities when they get older, so the answer is Yes to the one year old feeling separation.
Children are attached to their mothers because of a special bond and in such a case, the child will definitely feel there is something amiss if separated. The mother spends most time with the child who gets accustomed to it. Other people who the child is with everyday will also make the child feel a separation when the person is no longer there. It might result in a lot of tantrums and fussing the child usually does not have especially for people she does not relate with.