Assertion (a) : superumerary chromosomes do not usually have nay effect on the phenotype and Hence ,are geneticallyy unnecssery.
Reason( R ) : in some plants supernumerary chromosomes result in decrased vigour.

Options

A. Both (a) and (R ) are true (r ) is the correct explanation of (A)
B. both (A) and(R ) are true but (R ) is not the correct explanations of (A)
C. (A) is true statement but (R ) is false
D. Both (a) and (R ) are false

Answer

B