Structure And Mechanism Of Eukaryotic Chromosomes

1. Eukaryotic chromosomes are made from a material called chromatin. Explain what chromatin is and describe the chromatin structure of eukaryotic chromosomes.
2. Describe the changes in chromatin structure that occur during mitosis.
3. Explain the mechanism of mitotic chromosome separation (anaphase), and include in your answer the following terms: centromere, centrosome, kinetochore, sister chromatids and spindle fibres.
4. Define what is interphase and explain what is happening during this part of cell cycle.
5. What can the percentage of total cells in each phase of cell cycle tell you about the duration of each phase? 

Chromatin and its Structure in Eukaryotic Chromosomes

Chromatins are a complex of nucleic acids either RNA or DNA that condenses to a chromosome during cell multiplication. In eurokaryotic (organisms with membrane bound nucleus) cells the chromatin is found within the nucleus where it helps in packaging of DNA into smaller volumes so as to fit in a cell. It also strengthens the DNA to allow for the process of meiosis and mitosis

The chromosomes contain long DNA strands that carry genetic information. The eukaryotic cells have large genomes than prokaryotes that has multiple and linear chromosomes. However, the length plus linear nature of the chromosomes increases the ability of keeping the genetic material organized as well as of passing the correct amount of DNA to every daughter cell during the process of mitosis.

During the initial phase, interphase chromatin remains in condensed form as well as appears loosely distributed in the entire nucleus. Condensation of the chromatin starts during the prophase stage where the chromosomes become visible and remains condensed in the rest of the phases of mitosis up to the final stage telophase.

Before the commencement of anaphase, a replicated chromosomes reoffered to as sister chromatids are aligned at the centre of the cell.  The sister chromatids are joined at the centromere where during this stage each chromosome pair is separated into two chromosomes that are identical and independent. The chromosomes are then separated by the mitotic spindle which is made up of microtubules that are attached to the chromosome at one pole as well as to the end of a cell at the other pole.  However, the sister chromatids are divided concurrently at the centromere where the separate chromosomes are pulled by a  spindle to the other sides of the cell.

 Interphase is a stage of the cell cycle where a cell spends most of its life. During this stage, the cell duplicates their DNA as it prepares for mitosis. Interphase can be defined as the metabolic stage of a cell where it get’s nutrients as well as metabolizes them , reads the DNA and performs other functions of the cell.  A vast number of eukaryotic cells spend most of their time in this phase where a cell gets ready for meiosis or mitosis. Diploid cells or somatic cells of the body go through mitosis so as to reproduce themselves via cell multiplication whilst diploid germ cells go through meiosis   to form gametes for reproduction.

The distribution of cells continues to decline as a cell undergoes meiosis or mitosis from the initial stage, interphase to telophase.

                         

Mitotic index for the control group    = (30/350) × 100

= 8.57%

Mitotic index for the dark cellar on earth = (12/312) × 100

      = 3.85%

Mitotic index for the sunlight on earth in babybio plant feed     = (72/480) ×100

         = 15%

Mitotic index value for sunlight in space station       = (60/480) ×100

= 12.5%

Growth condition	Interphase	metaphase	Mitotic index
Control group (in sunlight on earth)	320	7	8.75%
In dark cellar on earth	300	2	3.85%
In sunlight on earth with babybio plant feed	408	19	15%
In sunlight in space station	420	16	12.5%

                               

Changes in Chromatin Structure During Mitosis

Mitotic cells= (P+M+A+T)*100

Mitotic cells counted for dark cellar =7+2+2+1=12

Control sunlight dataset’s mitotic cells=11+7+8+4=30

 Mitotic cells counted for baby bio=30+19+15+8=72

Mitotic cells counted for space=26+16+14+4=60

	Dark cellar	Control sunlight data set	Marginal tow total
Interphase	300	320	620
Mitotic cells	12	30	42
Marginal column totals	312	350	662(grand total)

Using the fisher’s exact test, the statistical p value is 0.01586.  The result is significant at p < 0.05

	Babybio plant feed	Control sunlight dataset	Marginal row total
Interphase	408	320	728
Mitotic cells	72	30	102
Marginal column totals	480	350	830(grand total)

The fisher test statistical P –value is 0.00534 and the result is significant at P< 0.05                                                                                                                                                                                                      

	Space station	Control sunlight dataset	Marginal row total
Interphase	420	320	740
Mitotic cells	60	30	90
Marginal column totals	480	350	830 (grand total)

The fishers exact test statistical value is 0.089529. The result is not significant at P< 0 .05

A table of the resulting P values

In the dark cellar category, the p value is 0.01586 which is significant at p < 0.05 while in the babybio plant feed, the resulting P value is 0.00534 which is significant at  P<0 .05. Lastly, in the space station the P value is 0.089529 which is not significant at p<0.05

Categories	Resulting P-value
Dark cellar	0.01586
Babybio plant feed	0.00534
Space station	0.089529

The smaller the mitotic index the more significant the p value. From the dark cellar condition , it can be deduced that the smaller the ratio between the number of cells undergoing mitosis versus those not undergoing  leads to an increase in the growth of onion roots where the calculated p value is less than the critical value.

The larger the mitotic index, the smaller the p value becomes. From the sunlight with babybio plant feed condition , it can be concluded that the larger the ratio between number of cells in a population undergoing mitosis and those not undergoing will lead to a decreased p value which is less significant to the critical value

In space station, the larger the mitotic index the larger the value of P which is not significant. this is because the calculated p value is larger compared to the critical p value hence the faster growth of onion  roots due to rapid cell division.

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Growth condition	Mitotic index	p-value
In dark cellar	3.85%	0.01586
Sunlight with babybio plant feed	15%	0.00534
In space station	12.5%	0.089529