Without using the word heredity, information, or blueprint - PRECISELY
write out what a gene is?

cannot use the words stated in definition

A gene is part of a chromosome that consists of a linear sequence of
nucleic acids that encodes the sequence of a protein.

The sequence is decoded(expressed) by transcriptional, and
translational cellular processes...

You really must understand the basics of cell biology to precisely
understand what a gene is.

Your body is composed of millions (billions) of cells.  In each cell
(except red blood cells), there is a nucleus.  In each nucleus there
are 23 pairs of chromosomes, one set from mom and one set from dad.

To oversimplify, each chomosome can be thought of as a string of
molecules.  Luckily, there are only four different kinds of molecules,
known as A, T, C and G.  (Those are abbreviations really).

Certain sequences of these four molecules can be found on this
string... which correspond to proteins inside your body.  Therefore, a
gene can be thought of as a sequence of A,T,C,and G's that correspond
to the formation of a single protein in the human body.

Hopefully this helps :)

Here are some additional links:

Basics of Cell Biology
http://www.uic.edu/nursing/genetics/Lecture/Molecular/basic_cell_biology.htm

Slightly more Advanced
http://www.bioteach.ubc.ca/CellBiology/StudyingGeneFunction/

Detailed Look at the History of Genetics
http://www.mala.bc.ca/~johnstoi/darwin/sect5.htm