question_answer

Which event involves in crossing over?

A)                  Chromosomes are short and thick

B)                  Exchange of genetic material

C)                  Pairing of chromosomes

D)                  Addition of chromosomes

Correct Answer: B

Solution :

                 Crossing over is an essential element of meiosis occurring during prophase, when non-sister chromatids of homologous chromosomes exchange portion of DNA strands.                 Chromosomes become thick and short during prophase and formation of mitotic spindle takes place. Pairing of chromosome occurs in prophase-I of meiosis-I. With the genes of the chromosomes thus aligned, a DNA strand of one homologous can pair with the complementary DNA stand of the other. The process of pairing is called synapse.