Question
Question: The longest phase of meiosis is a. Prophase I b. Prophase II c. Anaphase I d. Metaphase II...
The longest phase of meiosis is
a. Prophase I
b. Prophase II
c. Anaphase I
d. Metaphase II
Solution
Meiosis was discovered by German biologist Oscar Hertwig in sea urchin eggs in 1876. It was first demonstrated by Van Benden but was described by Winiwarter. Farmer and Moore gave the term “meiosis”.
Complete answer:
Meiosis is a special type of cell division in which one parental cell divides twice to produce four daughter cells in such a way that the chromosome number and amount of DNA is halved, so it is also called reductional division.
Meiosis occurs in diploid germ cells of plants and animals and produce haploid gametes. It is formed of two cell divisions: Meiosis-I and Meiosis-II with no interkinesis or of short period in which no replication occurs.
Meiosis- I is divided into karyokinesis-I or cytokinesis-I.
• Karyokinesis-I is divided into four subphases- Prophase-I, Metaphase-I, Anaphase-I and Telophase-I. Prophase-I is again divided into five substages- leptotene, zygotene, pachytene, diplotene and diakinesis. It is the longest phase of meiosis.
• Metaphase-I is characterized by arrangement of bivalents in two equatorial plates. Anaphase-I is characterized by moving of homologous chromosomes towards opposite poles causing reduction in chromosome number. Telophase-I involves reorganization of the daughter nucleus at each pole.
• Cytokinesis-I may or may not occur. Interkinesis, when present, involves only protein and RNA synthesis but no S-phase and DNA replication.
• Meiosis-II is like Mitosis and involves separation of genetically modified sister chromatids so brings haploidy in DNA amount while meiosis-I brings reduction in chromosome number only.
• Meiosis is of three types- gametic meiosis, zygotic meiosis, and sporogenic meiosis.
Hence, the correct answer is option (A).
Note: Meiosis is significant in that it forms haploid gametes and produces new combinations of genes due to crossing over and random arrangement of bivalents at equator during metaphase-I so produces variations which help in evolution.