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. Given these facts, what can cause new alleles to appear among the following options:
- skin cells
 - coded genes
 - sperm and egg fuse
 - hair cells
 - the parent's sex cells
 - lung cells
 - male gametes
 - reproduction


 

     the parent's sex cells    