Question

A phenomenon occurring during prophase 1 of meiosis?
(A) Mutation
(B) Synapsis
(C) Translation
(D) Crossing over

Answer 1

Hint:
Meiosis is a specialized form of cell division in which the number o chromosomes is reduced to half. The reduction in chromosome number is achieved by one round of DNA replication followed by two rounds of chromosome segregation with no intervening round of DNA replication.

Complete step by step answer:
Meiosis 1, the first meiotic division, begins with prophase 1. It is referred to as a reductional division because the number of chromosomes is reduced to half after the completion of meiosis 1. Prophase 1 is divided into five sub-stages: Leptotene, Zygotene, pachytene, Diplotene, and Diakinesis. Leptotene is considered to end and the zygotene stage of prophase begins as soon as synapsis, or intimate pairing, between the two homologs, is initiated.
Synapsis often starts when the homologous ends of the two chromosomes are brought together on the nuclear envelope and proceeds inward in a zipper-like manner from both ends. Pairing and crossing-over are possible because of a small region of homology between the X and Y chromosome and not both or neither. Each pair of homologous chromosomes forms as a result of synapsis is called a bivalent (sometimes referred to as tetrad).

Option ‘B’ is correct

Note:
During prophase 1 a meiosis-specific proteinaceous tripartite structure, the synaptonemal complex, forms a scaffold to connect homologous chromosomes along their lengths. Synapsis is required to promote recombination between homologs in most organisms.