You are presented with the question "What can cause new alleles to appear?" and the following answer choices: 
- skin cells
 - coded genes
 - sperm and egg fuse
 - hair cells
 - the parent's sex cells
 - lung cells
 - male gametes
 - reproduction

Now knowing that amutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring and alleles arise by mutation, choose the best answer.


 

     the parent's sex cells    