Concept:
This question relates to biological theories of crime and theories of punishment in criminology.
Step 1: Evaluate Assertion A.
Modern criminology does not support the idea that genes alone determine criminal behavior. Environmental, social, psychological, and economic factors also influence criminal tendencies.
Therefore, Assertion A is incorrect.
Step 2: Evaluate Reason R.
The Expiatory Theory of punishment emphasizes repentance and moral reform. According to this theory, if an offender sincerely repents and expiates the wrongdoing, forgiveness may replace punishment.
Therefore, Reason R is correct.
Step 3: Draw the final conclusion.
Since Assertion A is false while Reason R is true, the correct option is:
\[
\boxed{\text{A is not correct but R is correct}}
\]