Agene that is present but is not physically shown is called

A gene that is present but is not physically shown is called Carrier gene

Explanation:

Gene is the fundamental physical and useful unit of heredity and they are comprised of DNA.  A few genes codes for protein synthesis whereas many others are involved in other metabolic as well as cellular process.

In people, genes differ in size from a couple of hundred DNA bases to in excess of 2 million bases.  Each individual has two duplicates of every quality, one acquired from each parent. Alleles are types of a similar quality with little contrasts in their grouping of DNA bases.

In some cases if the offspring receives mutated gene from any one of the parent and if the disease is not expressed in the offspring, it means that the offspring has carrier gene.  

littering streams           is the answer

because they are eaten by the frog and the frog getseaten by the snake and the snake by the eagle