Biology Mitosis Lab

Mitosis and Meiosis Cell Division Lab Part 1-MITOSIS summary: In this experiment first the stages of an onion cell undergoing mitosis are going to be observed and every stage is going to be detected and drawn on paper. A brief description to what is going on should be attached to the pictures. This is important to understand the basics of cell division which is necessary growth,repair and asexual reproduction. Second the number of cells undergoing each phase is going to be counted to figure out in which phase the cell remains the most.

If interphase is the stage in which the cell grows and prepares for cell division then the number of cells undergoing interphase will be the most. After cells were counted it came out that indeed the number of cells in interphase is the most followed by prophase, metaphase=anaphase and telophase. This makes us come to the conclusion that the longest phase for a cell is interphase in which the cell grows and gets ready to divide. The second longest in prophase in which the chromatin fibers start to form chromosomes. The other phases which follow are very short and quick. Introduction:

Mitosis is the division of the nucleus,providing equal amounts of nuclear material to the daughter cells,in eukaryotes. Equal amounts of chromosomes are provided for the forming daughter cells by replicating the DNA and chromosomes before the division. Mitosis occurs in somatic cells and produces 2 daughter cells. The whole process of mitosis consists of 5 stages. 1-Interphase:is the stage in which the cell rests and gets ready for division. Consists of 3 parts. -G1:number of organelles double,size increases. At the end of this phase is a G1 checkpoint which controls is the cell is ready for division or not. S:chromosomes are duplicated. -G2:special proteins and enzymes for cell division are synthesized. 2-Prophase:Centrioles move to opposite poles of the cell. Form spindle fibers which’ll become the microtubules holding the centromere. Chromosomes become visible as long threads and become shorter and thicker. Each chromosome joins another one forming sister chromatids attached in the middle by a centromere. Nuclear membrane dissolves. 3-Metaphase:spindle fibers from the centrioles attach to the chromosomes at the kinetochore lining the chromosomes in the center of the cell. -Anaphase: The centromeres divide and the sister chromatids separate.

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The spindle fibers full the chromosomes to different poles of the cell. 5-Telophase: When chromosomes have reached opposite poles a nuclear membrane forms around them. Chromosomes then untwist and stretch becoming invisible again. Spindle fibers break down. At the end of mitosis cytokinesis takes place which is the formation of a cleaved membrane between the two new formed cells to separate them. Materials: -onion root tip cells -microscope Procedure: 1-Observe the onion root tips under the microscope first at 100X and then at 400X. 2-Draw each phase of mitosis you see. -Write a brief description of what you observe in each phase under the picture. 4-Under 400X count the number of cells undergoing different phases. Record data. 5-Calculate the total number of cells. 6-Calculate the percent amount of time the cells spend in each phase. Analysis: The data we collected shows that 52% of the cells were in stage interphase. This indicates that more than the half of the cells are recovering from their previous division and preparing to divide again. 40% of the cells were in the second phase prophase while the other phases had a cell percentage number of ~2%. This denotes that prophase is the second longest phase.

This can be because it takes a longer time to duplicate the chromosomes than simply lining them up and pulling them apart. Conclusion: Our hypothesis that if interphase is the resting phase then it’ll be the longest was proven true by the data we got from the onion root tips. The number of cells undergoing interphase had the highest number supporting our hypothesis. The complement of interphase is very important for organisms. If interphase isn’t completed before division or if something goes wrong during it many problems could occur like mutations or other things which would affect the proper functioning of the organism.

The possibility of errors emerging in this experiment is very low. The only errors could be caused if something was wrong with the microscopes lens or objective. Another thing to be researched could be what factors effect mitosis and if the same process would still occur in a different environment. Part 2-MEIOSIS In this part the concept of meiosis which is the essential of sexual reproduction is going to be observed by using Sondaria fimicola a certain type of mushroom. The colors of the ascospores before and after meiosis are going to be observed to see whether there is crossing over or not.

If meiosis is occurring then the newly formed sequences will look different then the ones to begin with. Observe the S. fimicola undergoing meiosis. Look at the ascospores after meiosis and notice the pattern. If the changes are in a 4:4 manner there is no crossing over. If any series of 2 like 2:4:2 or 2:2:2:2 occur it means that crossing over took place. The results we got were composed of different sequences including both patterns with 4’s and 2’s which means that crossing over took place. *Because S. fimicola was not available for the lab,cards with pictures of it undergoing meiosis were used. Introduction:

Meiosis is a type of cell division which provides genetic variation by reducing the chromosome number to half and creating haploid cells. Later on a male and female haploid cell will join to form a diploid cell with the right number of chromosomes. Meiosis consists of one DNA replication and two nuclear divisions resulting in 4 daughter cells. The process which provides for genetic variation is crossing over. Crossing over occurs in the early stages when homologous chromosomes move together so that their chromatids form a tetrad. This is called synapsis and allows for the exchange of chromosome sections.

In our case the crossing overs will result in different colorings of the ascospores of the S. fimicoli. Materials: -Microscope -S. fimicola meiosis cards Procedure: 1-Study the different phases of meiosis on the cards. 2-Notice the difference between ascospores with sequences of 4’s and 2’s. 3-Count the amount of different sequences present. 4-From the data you gathered calculate the percentage of asci showing crossover. Analysis: Out of a total from 26 sequences only 6 were made up of 4‘s while 20 were composed of different structures of 2‘s. This tells us that 77% of the asci showed crossing over while 23% did not.

Conclusion: Our hypothesis that if meiosis is present the new formed asci will have different colors was supported by the outcome of our observations. The fact that different sequences of 2’s emerged from the first pattern of 4’s is prove that crossing over took place. Genetic variation is very important because it is a way of natural selection. Beneficial and strong genes are selected while the others are eliminated. (Survival of the fittest) For future research it could be researched if the crossing over happens randomly or whether there is some order to it and if could be controlled to get a 100% functioning ,ideal organism.

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