Meiosis is also called reductional division because it halves the chromosome number in the daughter cells than those in the parental cell. It is so as the parental cell divides twice, while the chromosomes duplicate only once. Meiosis is of three types on the basis of period and site of occurrence of meiosis. Answer the following questions on meiosis:
(i) Name the longest phase of meiosis-I and sequence of its subphase...
(ii) Define crossing over. Give its significance,
(in) State one difference between gametic meiosis and zygotic meiosis.

Explanation

(i)Longest phase of meiosis-I is Prophase. Its subphases are: Leptotene, Zygotene, Pachytene, Diplotene and Diakinesis.
(ii) Crossing over is exchange of genes between non-sister chromatids of homologous chromosomes during pachyteng stage of prophase-Iin the presence of recombinase enzyme. It causes recombinations of genes so produces variations.
(iii) Gametic meiosis occurs during gametogenesis in the gonads of animals except protozoans and produces haploid gametes, while zygotic meiosis occur during first division of zygote to lead to formation of haploid adult organism and is found in protozoans, algae and bryophytes.