Genes code for proteins: neurotransmitters, hormones, and the enzymes that make and break them down.  Each of these are built out of amino acids, so a gene is a 'shopping list' of amino acids that determine the function (and chemical shape!) of a protein, when the cell finally gets around to making it, AND a set of instructions.  The gene doesn't actually make proteins.  Instead enzymes "unzip" the DNA, an RNA 'photocopy' of the gene is constructed, and it's that photocopy that is whizzed off to the 'factory.'  When it reaches the 'factory' other enzymes cut the RNA apart so the 'factory' knows which protein has been called for, how to make it, and the 'factory' uses that Information to make it.

OK, that's groovy but WHY was THAT sequence initiated?

A protein came floating along that was produced by a 'factory' that was told to make that particular protein when the RNA 'photocopy' of another gene told it to.

THAT protein was produced when Yet Another 'factory' was switched on by RNA ... & so forth and so on ... continuously.

Prof. Sapolsky (Stanford) has observed:

Genes no more give instructions than telephone books.

You cannot understand genes without understanding their regulation by the environment.

Where "environment" is both the biochemical 'soup' floating around inside the human body (and how you think about it and how you feel about it at any instant) and the external world (and how you think about it and how you feel about it at any instant).  And both have feedback loops within themselves and to/from each other.

To make it more interesting, a neurotransmitter - say - will have different affects and effects on human behavior depending on which ... uh ... "part" of the brain it is running around in.  Dopamine, for example, is the "Pleasure" neurotransmitter and controlled by the levels of glucocorticoid (a steroid) released during stress.  Under short term stress this makes you feel good and helps you remember better.  Under long term stress, in the hippocampus (conscious memory,) it decreases Long Term Potentiation - makes you forget stuff, while in the amygdala (Flight.Fight/Fear¹) it goes on making you remember stuff better so you react quicker, so you are more sensitive to ever lesser amounts of stress so you develop PTSD ... and you don't know why.

Both kinds of memory (conscious and hardwired,) it turns out, is a neural network at the first levels of processing.  After about one or two levels - depending on what part of the brain is doing the processing - the signals merge into an undifferentiated mass of neurons where a shift to Associative Memory processing is made and the rest of the processing completed.  Meaning we have no idea how it works so we throw some polysyllabic words at it & hope no one notices.  

Genes are certainly an important part of this and it is certainly true genes are Inheritable.  There are some serious caveats when researching Inheritability of Personality, and, thus, Behavior.

Prof. Zuckermann, Psychobiology of Personality ISBN 0-521-01632-0 on the heritability of of personality traits:

1.  Heritability depends on the reliability of the phenotype measure.  

2.  Heritability can vary from one time to another.  [citing mores, sexual permissiveness, as examples]

3.  Heritability can vary from one population to another.

4.  Heritabilities apply to populations not to individuals.

5.  One cannot generalize from heritiabilities within populations to the source of differences between populations.

6.  Heritability is an imprecise statistic and requires large ns for stable results.

Thus the presence of a gene is indicative of ranges of potential behavior yet by no means are genes determinative nor, to make things fun, are they necessary.  Environment is just as prima facia indicative of actual, or potential, behavior.  And, as one can't eliminate molecular biology from behavior, one can't eliminate behavior from molecular biology.

¹  And Fucking.  This is a beneficent inheritance from some Tournament Sex practicing ancestor.  And one reason why sex is so 'iffy' in humans.

She believed in nothing; only her skepticism kept her from being an atheist. -- Jean-Paul Sartre