 First, a balancer carries a recessive lethal mutation, which makes the organism non-viable if two copies of balancer are inherited ( ie no copy of the desired mutation).
<coherence>  First, a balancer carries a recessive lethal mutation, which makes the organism non-viable if two copies of balancer are inherited ( ie no copy of the desired mutation).
 First, a balancer carries a recessive lethal mutation, which makes the organism non-viable if two copies of balancer are inherited ( i.e. no copy of the desired mutation).