Oh this is easy. 
Astronomy is the branch
        
             
        
        
        
Answer: Point mutation is easily reversible, thus non-lethal 
Explanation:
Point mutation is caused by exchange of a single nucleotide for another. These change is called
1) Transition (when a purine base substitute another purine base, or pyrimidine bases substitute each other)
2) Transversion (when a purine base substitute a pyrimidine base). 
However, note that a point mutation can be easily reversed by another point mutation; so, the claim that a nucleotide difference in the Hsr12 gene caused the human disease is inaccurate 
 
        
             
        
        
        
The hormone that stimulates ovaries to release one egg per ovarian cycle is called follicle-stimulating hormone (FSH). This hormone is produced in the pituitary gland. Most woman will reach puberty by their teen years. 
        
                    
             
        
        
        
Volcanic eruption would change the surface the quickest