Skin color<span> is due primarily to the presence of a pigment called melanin , which is controlled by at least 6 genes. Both light and dark complexioned people have melanin. However, two forms are produced--pheomelanin , which is red to yellow in</span>color<span>, and eumelanin , which is dark brown to black</span>
        
             
        
        
        
Answer:
Photosynthesis and cellular respiration allow the carbon and oxygen that organisms consume and produce to be cycled through the ecosystem. They work together so that what is made from one process is used in the other. Without them the ecosystem would run out of carbon dioxide and oxygen, and everything would die.
 
        
             
        
        
        
Answer:
Natural selection disrupts the genetic equilibrium by favoring the genes for the traits that impart survival advantage to individuals. 
Explanation:
Natural selection refers to the unequal survival rate of individuals of a population due to the presence of some beneficial adaptive genetic trait. These individuals are able to survive more and leave more progeny. Over generations, the population has increased number of these individuals leading to evolution of a population with different allele frequencies.  
For example, the frequency of gene for antibiotic resistance in the bacterial population was increased once humans started using antibiotics to control the bacterial population. This led to the evolution of the bacterial population with antibiotic resistance.