Q18 / 180 · NEET 2016 (Phase 2) · Botany

Match the stages of meiosis of Column-I to their characteristic features in Column-II and select the correct option using the codes given below:
 
Column-I Column–II
a. Pachytene (i) The pairing of homologous chromosomes
b. Metaphase I (ii) Terminalization of chiasmata
c. Diakinesis (iii) Crossing-over takes place
d. Zygotene (iv) Chromosomes align at the equatorial plate

  • Correct answer
    A
    \(\begin{array}{|l|l|l|l|} \hline a & b & c & d \\ \hline \text { (iii) } & \text { (iv) } & \text { (ii) } & \text { (i) } \\ \hline \end{array}\)
  • B
    \(\begin{array}{|l|l|l|l|} \hline a & b & c & d \\ \hline \text { (i) } & \text { (iv) } & \text { (ii) } & \text { (iii) } \\ \hline \end{array}\)
  • C
    \(\begin{array}{|l|l|l|l|} \hline a & b & c & d \\ \hline \text { (ii) } & \text { (iv) } & \text { (iii) } & \text { (i) } \\ \hline \end{array}\)
  • D
    \(\begin{array}{|l|l|l|l|} \hline a & b & c & d \\ \hline \text { (iv) } & \text { (iii) } & \text { (ii) } & \text { (i) } \\ \hline \end{array}\)

Solution

Zygotene: 

  • Chromosomes start pairing together. This process is called synapsis. The paired chromosomes are called homologous chromosomes. 
  • The formation of synapsis is accompanied by the formation of the synaptonemal complex. 
  • The synaptonemal complex by a pair of homologous chromosomes is called a bivalent or a tetrad.

Pachytene: 

  • Bivalent chromosomes clearly appear as tetrads, at this stage. 
  • Recombination nodules appear. These nodules are the sites at which crossing overtakes place between non-sister chromatids of the homologous chromosomes. 
  • The exchange of genetic materials between two homologous chromosomes takes place during crossing over. This leads to the recombination of genetic materials on the two chromosomes.

Diakinesis: 

  • Chiasmata is terminated at this stage. 
  • Meiotic spindles are formed to prepare the homologous chromosomes for separation. 
  • The nucleolus disappears and the nuclear envelope breaks down by the end of diakinesis.

Metaphase I: 

  • The bivalent chromosomes are aligned on the equatorial plate. 
  • Spindle fibres from opposite poles attach to the pair of homologous chromosomes.

Hence, the correct answer is option: 'A'.

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