Aset of characteristics believed to be shared by all members of a social category is a tendency for early information about someone weighs more heavily than later information in influencing one's impression of that person is called

The first answer is Stereotype. A stereotype is a set of qualities or characteristics that people consider to have an individual or social group that makes them different from the rest of the individuals. Stereotypes are often exaggerated and subjective because they are not based on real evidence.

The second answer is primary effect. This phenomenon refers to the way we encode the memory; we tend to remember more the first thing we learn or know about something or someone than the information acquired in the middle.

I hope my answer can help you.