Sister chromatids are two identical copies of Chromosome that is formed by the replication of a single chromosome.
This copies are formed during mitosis. Later on, these two sisters chromatids will grown into two different Cells 
<span />
        
             
        
        
        
Answer: I believe Meniscus tears are not healed on their own. 
Explanation: 
Because the two most common causes of a meniscus tear are due to traumatic injury (often seen in athletes) and degenerative processes (seen in older patients who have more fragile cartilage). The most common mechanism of a traumatic meniscus tear occurs when the knee joint is flexed and the knee is then twisted.  The meniscus tear can only be surgically removed. However, in some cases people can live with the meniscus tear without any problem. Also, there are exercises that lessen the symptoms of this problem. The most common symptoms of a meniscus tear are: Knee pain, Knee swelling, Tenderness when pressing the meniscus, Popping or clicking inside the knee, Limited knee joint movement.
 
        
                    
             
        
        
        
Fitness is the answer. 
Evolution is the process of a species changing. 
Mutation is also a species changing. 
Variation is the differences between animals of the same species.
        
                    
             
        
        
        
They unite to form a zygote then an embryo. Most produce both male and female gametes.