During cell growth, DNA synthesis takes place in

1. S-phase                       
2. ${\mathrm{G}}_1$-phase
3. ${\mathrm{G}}_2$-phase                     
4. M-phase 

A cell at telophase stage is observed by a student in a plant brought from the field. He tells his teacher that his cell is not like other cells at telophase stage. There is no formation of cell plate and thus the cell is containing more number of chromosomes as compared to other dividing cells. This would result in

(1) polyploidy

(2) somaclonal variation

(3) polyteny

(4) aneuploidy

Spindle fibres attach on to 

In meiosis crossing over is initiated at 

1. leptotene

2. Zygotene

3. diplotene

4. pachytene

DNA replication in bacteria occurs

(1) during S-phase

(2) within nucleolus

(3) prior to fission 

(4) just before transcription 

During cell growth, DNA synthesis takes place in:

Which of the following options gives the correct sequence of events during mitosis?