Genetics (B 252) Lab 2016-2017 Mitotic Index The percentage of cells undergoing mitosis or it is defined as the ratio of no. of cells in the dividing phase to the total number of cells observed. This will help to identify the region of most mitotic activities. Mitotic index is used to quantify the differences in cell division when environmental parameters are changed. Mitotic index decreases with increasing distance from root tip. That means gradual decrease in cell division as it moves from the zone of cell division to the zone of cell elongation. The meristematic region in the root tip is the actively growing region and thus the mitotic index is high. An elevated mitotic index indicates more cells are dividing. How to calculate? Mitotic index = total number of cells in all phases of mitosis / total number of cells % cells in mitosis = total number of cells in all phases of mitosis x 100/ total number of cells Duration of Cell Cycle: The division cycle of most eukaryotic cells is divided into four discrete phases: G1, S, G2 and M. The M phase (mitosis) is usually followed by cytokinesis. The duration of these cell cycle phases varies considerably in different kinds of cells. How to calculate? The duration of Stage in the cell cycle (minutes) = (number of cell in stage / total number of cells) x Cell Cycle duration of the organism Where the cycle duration of higher plants =1440 min (divide every 24 hr). Where the cycle duration of yeast = 120 min (divide every 2 hr). 1 Genetics (B 252) Lab 2016-2017 Problem: Data were collected from a microphotograph of onion and bean root tips when they are dividing, showing the following data: Stage of cell # cells in the stage cycle Onion Bean Interphase 64 60 Prophase 18 14 Metaphase 5 10 Anaphase 6 11 Telophase 9 7 Total number of 102 cells 102 cells cells - Calculate the mitotic indices and the duration of the stages in the cell cycle in both cases as minutes for both plants. Where the cycle duration=1440 min (divide every 24 hr). - Comment on your results. 2 Genetics (B 252) Lab 2016-2017 Student name: Code number: STUDENT’S ASSIGNMENT Give it to your laboratory instructor Problem: Data were collected from microphotographs of both treated and control Onion root tips when divided, showing the following data: Stage of cell cycle Number of cells in the stage Control Onion Treated Onion Interphase 66 53 Prophase 18 19 Metaphase 10 20 Anaphase 7 10 Telophase 9 8 Total number of cells 110 cells 110 cells - Calculate the mitotic indices and the duration of the stages in the cell cycle in both cases as minutes. - Comment on your data. 3 .