Genetics Lab - Lab Report 1 Mitosis – Meiosis.pdf

INTRODUCTION: • Mitotic cell division is the type of cell division that results in the formation of two genetically identical daughter cells from a single mother cell.. • Mitosis produc

VIETNAM NATIONAL UNIVERSITY HO CHI MINH CITY –

INTERNATIONAL UNIVERSITY

GENETICS LAB - LAB REPORT 1

Lecturer: Prof Tong Thi Hang Class: Tuesday Afternoon Date of submission: 03/10/2022

GROUP NUMBER: 03

GROUP MEMBERS:

Table of contents

I MITOSIS REPORT 3

1 INTRODUCTION: 3

2 PROCEDURE: 4

2.1 Materials: 4

2.2 Procedure: 4

3 RESULT: 5

4 DISCUSSION 7

4.1 What is mitosis, where can we find mitosis? 7

4.2 How can a cell determine the metaphase plate? 8

4.3 What is the difference between anaphase and telophase? 8

4.4 Why do we have to use Carnoy’s solution? 8

4.5 Why do we have to use 70% ethanol to store the sample until used? 8

II MEIOSIS REPORT 9

1 INTRODUCTION 9

2 PROCEDURE 10

2.1 Material 10

2.2 Procedure 10

3 RESULT 11

3.1 Meiosis I 11

3.2 Meiosis II 13

4 DISCUSSION 15

4.1 Compare the similarities and differences between mitosis and meiosis 15

4.2 Why can’t we put a picture of tetrad of microspores in this report? 16

4.3 What are the two special events occurring during meiosis? 16

4.4 Compare the similarities and the differences between mitosis and meiosis II 16

III REFERENCES 17

I MITOSIS REPORT

1 INTRODUCTION:

• Mitotic cell division is the type of cell division that results in the formation of two genetically identical daughter cells from a single mother cell

• Mitosis produces two daughter cells that are identical to the parent cell If the parent cell is haploid (n), then the daughter cells will be haploid If the parent cell is diploid, the daughter cells will also be diploid This type of cell division allows multicellular organisms to grow and repair damaged tissue

• There are four basic phases of mitosis:

o Prophase: chromosomes can be seen as it coils and condenses and each of them is in duplicated form attaching to the spindle via kinetochore Sister chromatids' kinetochores are attached to spindles that come from the cell's opposing poles The nucleolus vanishes after the nuclear envelope disintegrates

o Metaphase: chromosomes condense at the highest level and stand in a line at the equatorial plate of the spindle Each pole separates the sister chromatids from one another, but they are still attached together

o Anaphase: with the help of spindle fibers, sister chromatids of each chromosome separate and are pulled apart to the two opposite ends of the spindles The chromatids form V-like structures with the centromeres pointing toward the respective poles

o Telophase: chromosomes relax Spindle apparatus breaks down Cytokinesis happens, a nuclear membrane appears to surround each group of chromosomes at two poles At the end, there are two daughter cells that are identical to the parent cell

• In this practical lesson, we observed different phases of mitosis under the microscope in order

to know how cells can grow and repair

2 PROCEDURE:

2.1 Materials:

• Onion bulbs

• 2M HCl

• 70% glycerol

• 70% and 90% Ethanol

• Aceto orcein stain

• Carnoy’s solution

• Microscope

• Microscope slides and coverslips

• Watch glasses

• Forceps

• Dissecting needle

• Culture dish

2.2 Procedure:

1 Using a forceps to transfer some onion roots into a watch glass

2 Cut the root tip about 5 millimeters

3 Wash the roots with water for 3 times to remove all the ethanol

4 Remove all water by using the pipette

5 Soak the roots in several drops of 2M HCl and heat it with low fire

6 Cover it with a piece of culture dish for 15 minutes to soften them

7 After that, wash the roots 2 times with water to remove HCl

8 Soak the roots in aceto orcein stain and heat it on the low fire to stain beautifully

9 Cover it with a piece of culture dish and wait for 20 minutes to stain the chromosomes

10 Add one drop of 70% glycerol at the middle of a microscopic slide then transfer one stained onion root into it

11 Cover the root with a coverslip Remove all the bubbles

12 Apply pressure over the cover glass to squash the root tip into a thin layer

13 Use the 4X objective len first to identify the meristem area After that, turn to higher power objective lenses (10X and 40X) to observe the cells in different stages of mitosis

3 RESULT:

Prophase

Figure 1: Prophase

This is the late prophase

Chromosomes fully condense This

is when they begin to assemble into chromatids and centromeres Besides, the nuclear envelope breaks down and the nucleus disappears

Metaphase

Figure 2: Metaphase

In metaphase, chromosomes are arranged horizontally in the metaphase plate

Anaphase

Figure 3: Anaphase

During anaphase, the pulling force

of centrioles makes chromatids of each chromosome separate and move to the opposite sites of the cell

Telophase

Figure 4a: Early telophase

In the early telophase, chromatids of each chromosome reach to their respective and start decondensing The cell plate is reformed However,

in this picture, it is still a bit early so the cell plate cannot be observed

Figure 4b: Late telophase

Cytokinesis occurs during the late telophase Cell plate reform Chromosomes decondense The nuclear envelope is rebuilt from fragments of the old nuclear envelope and other endomembrane system components Theoretically, it will result in two daughter nuclei with genetically identical copies However, in this picture, chromosomes do not decondense enough to observe that

4 DISCUSSION

4.1 What is mitosis, where can we find mitosis?

• Mitosis is a type of cell division that occurs in all organisms except viruses Mitosis results in body cells and are used as a mode of asexual reproduction It involves only one cell division, producing two daughter cells (diploid) genetically similar to each other

• Because it generates new cells for growth and the replacement of worn-out cells, mitosis is absolutely necessary for life A parent cell divides into two identical daughter cells during the mitotic process Mitosis is therefore necessary for the synthesis of new membranes, fibers, and tissues Additionally, the fact that almost all living things undergo mitosis makes this cellular process extremely significant Numerous examples of how the process of mitosis aids organisms in self-healing and growth can be found in the context of humans When the human body heals itself after harm, when adolescents go through growth spurts, or when the body develops new muscle after exercise, these are examples of mitosis

• In plants, mitosis takes place in the meristems, which are found at the ends of the stems and roots These two regions are in charge of creating all the cells that plants require to grow The stems, side branches, and root tips are where mitosis occurs most quickly

• In the human body, mitosis takes place in somatic cells, which refers to all cell types not involved in the production of gametes For instance, red blood cells only live for about 4 months Mitosis is the process by which the body produces fresh red blood cells

4.2 How can a cell determine the metaphase plate?

The mechanical forces of the microtubule spindle fibers produced from the centrosome are necessary for the formation of the metaphase plate, also known as the equatorial plate At the metaphase plate, the chromosomes are evenly spaced out This is because spindle fibers, which come from opposite poles of the cell, are physically pulling in opposite directions at the same time If we imagine the centrioles lie at the north and south of a circular cell, the metaphase plate would be the line in the middle of the cell and run from east to west

4.3 What is the difference between anaphase and telophase?

• Anaphase: chromosomes break at centromeres, sister chromatids move away from the equatorial plate to the opposite poles of the cell Chromosomes or sister chromatids separate due to the pulling tension generated by the spindle apparatus The chromosomes in this phase are condensed

• Telophase: chromosomes arrive at opposite poles, and nuclear envelope material surrounds each set of chromosomes The contracted microtubules are further loosened, increasing the length of the cell The chromosomes unfolded back to chromatin

4.4 Why do we have to use Carnoy’s solution?

Carnoy's solution is a fixative It will help us to preserve the tissue and cells as life-like as possible, without any shrinking or swelling and without distorting or dissolving cellular constituents Therefore, we can observe the sample as comprehensively as possible

4.5 Why do we have to use 70% ethanol to store the sample until used?

Since ethanol removes water from cells and tissue, it dehydrates the tissue while also preserving DNA The water-soluble compound ethanol alcohol has an anti-microbial action mechanism that involves dehydrating or denaturing proteins and inhibiting the production of metabolites, which are essential for quick cell division Because it is less expensive and keeps specimens somewhat flexible, allowing for later morphological study, 70% ethanol is frequently used instead of 96-100% Additionally, pure alcohol has a limited capacity to penetrate cell walls, immediately coagulate protein, and create a barrier that protects other proteins Instead, if we use 100% ethanol, the bacteria become "sealed" and continue to live

II MEIOSIS REPORT

1 INTRODUCTION

• Meiosis also called reduction division, division of a germ cell involving two fissions of the nucleus and giving rise to four gametes, or sex cells, each possessing half the number of chromosomes of the original cell

• Meiosis produces daughter cells (haploid) which have a half of the number of chromosomes present in their parent cell (diploid) This process leads to the reduction in the number of identical chromosomes from two into one (2n → n)

• The period between meiosis I and meiosis II is <interkinesis=in which the spindle disintegrates, the chromosomes relax, and the nuclear membrane reforms around the chromosomes grouped

at each pole

• Meiosis includes two rounds of division, called Meiosis I and Meiosis II Each round goes through 4 phases Each of these divisions is divided into prophase, metaphase, anaphase, and telophase

o Meiosis I

- Prophase I: chromosomes condense, the nuclear membrane and nucleoli begin to disappear, the spindle forms Crossing over between the chromosomes in the homologous pair happens

- Metaphase I: homologous chromosomes align at the equatorial plate of the spindle Homologous chromosomes align at the equatorial plate of the spindle

- Anaphase I: Homologous chromosomes align at the equatorial plate of the spindle

- Telophase I: 2 daughter cells are formed and start to undergo Meiosis II However, do not completely uncoil

o Meiosis II

- Prophase II: The duplicated chromosomes recondense Nuclear membrane disintegrates again while formation of spindle is seen in each daughter cell

- Metaphase II: The duplicated chromosomes line up into one row at the equatorial plate of each spindle

- Anaphase II: the sister chromatids separate and are pulled towards opposite poles of the cell

- Telophase II: nuclear membranes form around each set of chromosomes, and the chromosomes decondense Cytokinesis splits the chromosome sets into new cells, forming the final products of meiosis: four haploid cells in which each chromosome has just one chromatid

• Meiosis helps in producing gametes and pass genetic materials to the next generation but still maintaining its number of chromosomes sets via sexual reproduction Moreover, meiosis is also

an important process that creates combinatorial variation that contributes to the diversity of organisms’ world

• In this practical lesson, we observed available samples under a microscope and determined which phases are they

2 PROCEDURE

2.1 Material

• Garlic chive flower

• 70 % and 90% Ethanol

• Carnoy’s solution

• Aceto-orcein stain

• 2M HCl

• 10% glycerol

• Microscope

• Microscope slide & coverslip

• Dissecting needle

• Forceps

• Immersion oil

2.2 Procedure

1 Use forceps to transfer garlic chive flowers into the watch glass Then, use dissecting needles to remove the perianth and petals from the flowers, only retain the anthers

2 Wash the anthers with water 3 times and remove water

3 Add 5 drops of 2M HCl solution, heat it in 2 seconds Cover the watch glass and soak the anthers in that for 15 minutes

4 Wash the anthers with water 3 times, then remove water

5 Add 2 drops of aceto-orcein stain into the watch glass Heat it in 2 minutes and cover it in

30 seconds, repeat this step 3 times

6 Soak the anthers in a staining solution for 30 minutes or more

7 Transfer four stained anthers to a microscope slide, which is pre-mounted with one drop of 10% glycerol Cover with a coverslip

8 Use the handle of the dissecting needle to apply pressure over the coverslip gently

9 Observe the specimen under a low power objective to identify the area with many dividing cells Then use a higher power objective lens to carefully observe cells with different meiotic phases

3 RESULT

3.1 Meiosis I

Prophase I

Figure 1: Prophase I

In this phase, chromosomes condense The nuclear membrane and nuclei cannot be observed since they are already broken down Also, this is when

<crossing over= happens

Metaphase I

Figure 2: Metaphase I

During metaphase I, chromosomes

in the homologous pair are fully condensed and line up in the metaphase plate

Anaphase I No figure

In anaphase I, the centrosomes do not divide Therefore, the chromosomes of each homologous pair instead of the chromatids move to the opposite site of the cell

However, because the anther sample itself may have already undergone this process or not yet, the figure of metaphase I cannot

be observed

Telophase I No figure

During telophase I, chromosomes move completely to the spindle poles and the cell plate reforms This is followed by the division of cytoplasm Chromosomes in the phase do not uncoil completely in order to be ready to enter to the prophase of meiosis II

Yet, because the anther sample itself may have already undergone this process or not yet, the figure

of telophase I cannot be observed

3.2 Meiosis II

Prophase II No figure

Chromosomes condense, the spindle forms, and the nuclear envelope disintegrates However, the specimens have not

or already entered Prophase II so the picture of this phase cannot be observed

Metaphase II

Figure 3: Metaphase II

Individual chromosomes line up

on the metaphase plate

Anaphase II No figure

Sister chromatids separate and migrate as individual chromosomes toward the spindle poles

But, because the specimens have not or already entered Anaphase

II, the picture of anaphase II cannot be observed