18
The diagram shows a bivalent at prophase-I of meiosis. Which of the four chromatids can cross over?
Explanation
The homologous chromosomes lie parallel to each other in leptotene stage. Each chromosome has four chromatids and are bivalent. The non-sister chromatids of homologous chromosomes cross over in pachytene stage of prophase- I.
19
If a tissue has at a given time 1024 cells, how many cycles of mitosis had the original parental single cell undergone?
Explanation
The parental cell undergoes 10 divisions of mitotic cycle to give 1024 cells.
20
An anther has 1200 pollen grains. How many pollen mother cells must have been there to produce them?
Explanation
Three hundred pollen mother cells have to be there to produce 1200 pollen grains. because one pollen mother cell will produce four pollen grains.
21
At what stage of cell cycle does DNA synthesis take place?
Explanation
Synthetic phase or S-phase of interphase, is the stage of cell cycle where DNA synthesis or replication takes place.
22
It is said that the one cycle of cell division in human cells (eukaryotic cells) takes 24 hours. Which phase of the cycle, do you think occupies the maximum part of cell cycle?
Explanation
If a cell takes 24 hours to divide, it will have 18-20 hours time to spend on interphase stage to prepare itself to undergo cell division.