A measure of tactile acuity defined as the smallest separation at which two points applied simultaneously to the skin can be clearly distinguished from a single point. It varies from 1 or 2 millimetres in the finger pads and tongue to more than 60 millimetres on the upper arm, upper thigh, and back.
        
             
        
        
        
Overdominance occurs when a heterozygote has a more phenotype than that of either of its parents.
        
             
        
        
        
FALSE : the presence of harmful substances in the earth’s atmosphere is called air pollution