MEIOSIS WORKBOOK - thiacin...Meiosis 1. Do you know the significance of meiosis. 2. Do you know how genetic variation occurs during meiosis. 3. Can you compare and contrast mitosis

T R L J. Version 2, 2018

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NAME:___________________________ OPTION GROUP:__________________

CELL DIVISION

MEIOSIS

WORKBOOK


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Instructions

Regular revision throughout the year is essential. It’s vital you keep a track of what you understand and what you don’t understand. This booklet is designed

to help you do this. Use the following key to note how well you understand the work after your revision. Put the letter R, A or G in the table. If you place an

R or an A then you should make a note of what you are struggling with and the end of this book under the relevant section and seek help with this.

Key R = Red. I am not confident about my knowledge and understanding A = Amber. I am fairly confident about my knowledge and understanding G = green. I am very confident about my knowledge and understanding

STUDY CHECKLIST AND ASSESSMENT OBJECTIVES


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The following points are what you need to know, revise and answer questions on.

Place an R, A or G when you have revised and make notes of what you do not understand.

Cell Division Meiosis

1. Do you know the significance of meiosis.

2. Do you know how genetic variation occurs during meiosis.

3. Can you compare and contrast mitosis and meiosis.

4. Do you know the meaning of haploid and diploid.

5. Can you recognise a cell in each of the stages of meiosis from drawings and microscope images.

6. Can you describe what evens are occurring during prophase I, metaphase I, anaphase I telophase I, prophase II, metaphase II, anaphase II, telophase II. Also, cytokinesis.

7. Do you know when a cell becomes haploid and when the DNA content halves during meiosis.

8. Do you know the difference between a replicated and a non-replicated chromosome.

9. Can you state where meiosis occurs in both plants and animals.

9. Can you state where meiosis occurs in both plants and animals.

Assessment Objective Description AO1 Demonstrate knowledge and understanding of scientific ideas, processes, techniques and procedures.

AO2 Apply knowledge and understanding of scientific ideas, processes, techniques and procedures:

• In a theoretical context

• In a practical context

• When handling qualitative data

• When handling quantitative data

AO3 Analyse, interpret and evaluate scientific information, ideas and evidence, including in relation to issues, to:

• Make judgments and reach conclusions

• Develop and refine practical design and procedures


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Below is a list of some key words and phrases you will need to learn and understand in this water topic.

1. Anaphase

2. Anther

3. Bivalent

4. Cell cycle

5. Centromere

6. Centromere

7. Chiasmata

8. Crossing over

9. Cytokinesis

10. Diploid

11. Egg

12. Equator

13. Haploid

14. Homologous chromosomes

15. Meiosis

16. Meiosis I

17. Meiosis II

18. Metaphase

19. Mitosis

20. Mitotic Index

21. Mutation

22. Pole

23. Pollen

24. Pollen sac

25. Prophase

26. Random assortment

27. Sister chromatids

28. Sperm

29. Spindle fibres

30. Telophase

WORD BANK


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1.0 SUMMARY OF MITOSIS 1.0.1 – 1.0.6 Key concepts and terminology of meiosis

1.0.1 Concept Meiosis has two divisions called meiosis I and Meiosis II.

1.0.2 Concept Meiosis I has the following stages: interphase, Prophase I,

Metaphase I, Anaphase I and Telophase I with cytokinesis. Meiosis II

has the following stages: Prophase II, Metaphase II, Anaphase II and

Telophase II and cytokinesis.

1.0.3 Concept Meiosis produces 4 daughter cells. These daughter cells are

referred to as gametes which are haploid and show genetic variation.

Two daughter cells are formed at the end of meiosis I and two others

at the end of meiosis II, as shown below:

1.0.4 Concept The function of meiosis is in sexual reproduction in which haploid

gametes are produces. There are two different gametes, the male

sperm and the female egg. In a mammal sperm is produced in the

testes and in a female the egg is produced in the ovaries. In a plant

the male gametes is the pollen which is produces in the pollen sacs of

the anther and the female egg is produces in the ovary.

On the next page are images of the anther of a plant:


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Transverse section through an anther drawing and microscope image. Each anther has 4 pollen

sacs in which are the pollen grains.

Pollen sac containing pollen grains

Magnified view of a single pollen sac.

Two daughter cells formed by meiosis I.

Four daughter cells formed by meiosis II.


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1.0.5 Overview of meiosis

1.0.6 Graphical overview of meiosis

Cell 1

Cell 2

Cell 3

Cells 4

Cells 5

This cell has 4 chromosomes which are in homologous pairs, so there are two pairs of homologous chromosomes. The cell is diploid (2n) and has a DNA content of 4 AU. The chromosomes are non-replicated so do not have an X shaped.

This cell has undergone interphase, so the chromosomes have been replicated to form X shaped structures. The cell contents have doubled to 8 AU.

This cell is in prophase I. The homologous chromosomes have come to lie close together and are called bivalents. Crossing over occurs to create genetic variation.

These cells have been formed by meiosis I. The cells are haploid because the chromosomes are not in homologous pairs. The DNA content has halved to 4 AU.

These cells have been formed by meiosis II. The cells are haploid because the chromosomes are not in homologous pairs. The DNA content has halved to 2 AU. The chromosome number as halved to 2. These cells are called gametes.

DN

A C

on

ten

t A

U

4

8

2

Cell 1

Cell 2 & 3

Meiosis I

Cells 4

Meiosis II

Cells 5


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2.0 STAGES OF MEIOSIS

2.0.1 Concept Prophase I is a highly modified stage compared to prophase of mitosis. The chromatin condenses to form visible chromosomes that are X shaped.

2.0.2 Concept Genetic variation is created during prophase I by a process called crossing over. This is shown below.

2.0.1 – 2.0.2 Prophase I

Cell taken from an anther

Homologous chromosomes in the nucleus.

Homologous chromosomes come together by a process called synapses

to form bivalents.

Non-sister chromatids, i.e. chromatids from the maternal and paternal

chromosome cross over. The point at which the non-sister chromatids

join is called a chiasmata. Real chiasmata are shown below:

Chiasmata

Lengths of DNA are exchanged between the sister chromatids. The

chromosomes are know genetically different and show genetic

variation


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2.0.3 – 2.0.4 Metaphase I

2.0.3 Concept The homologous chromosomes align along the equator and attached to the spindle fibers via the centromere. Each homologous pair of chromosomes are attached to the same spindle fiber.

2.0.4 Concept Metaphase is also the stage that genetic variation can be created. The method it is created is by random assortment (also called independent assortment). With this method homologous chromosomes can align with the maternal or paternal chromosomes pointing to any of the two poles as shown simply in the image below. There are 8388608 potential different combinations created by random assortment (223).

2.0.3 Anaphase I

2.0.3 Concept During anaphase I the spindle fibres contract and pull the homologous chromosomes to opposite poles of the cell.


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2.0.3 Telophase I

2.0.3 Concept During telophase I the homologous chromosomes are at the poles of the cell and cytokinesis begins.

2.0.4 Prophase II

2.0.4 Concept In Prophase II there are two cells. Each cell has visible chromosomes. The chromosomes are not in homologous pars, so the cells are haploid.


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2.0.5 Metaphase II

2.0.5 Concept In metaphase II spindle fibres form but at right angles to those formed in meiosis I. The chromosomes are attached to the spindle fibres via the centromere.

2.0.6 Anaphase II

2.0.6 Concept In anaphase II the spindle fibres shorten and pull the sister chromatids to opposite poles of the cell.


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2.0.7 Telophase II

2.0.7 Concept In telophase II the sister chromatids have reach the poles and the two cells undergo cytokinesis. 4 gametes cells are produced, the chromosomes are single structure and the cells are haploid. The number of chromosomes have halved from 4 to 2.

3.0 THE SIGNIFICANCE OF MEIOSIS

2.0.6 Concept Genetic variation is created which allows organisms to adapt to new environmental conditions so to be able to survive.

2.0.7 Concept The daughter cells are haploid so when fertilization of the gametes

occurs the diploid number of chromosomes is restored.

2.0.8 Concept Mutations can occur during meiosis which increases the genetic variation.

2.0.9 Concepts There is random fusion of gametes at fertilisation which adds to the variation in the offspring.


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2.0.6 Concept The general reproductive life cycle of an organism involves both mitosis and meiosis as shown below:

4.0 COMPARISON OF MEIOSIS AND MITOSIS

Male Organism

2n

Female Organism

2n

n n

Zygotes

2n

Embryo

2n

Offspring

2n

Meiosis Meiosis

Fertilisation

Mitosis

Mitosis

Mitosis Meiosis

Diploid daughter cells Haploid daughter cells

One division Two divisions

2 daughter cells 4 daughter cells

Genetically identical daughter cells Genetically different daughter cells

No variation Variation created

No crossing over no random assortment Crossing over and random assortment occur in meiosis I

Chromosomes on different spindle fibres during metaphase

Homologous chromosomes on the same spindle fibre during metaphase II.


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QUESTIONS ON SECTION 1 TO 4

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Documents

MEIOSIS WORKBOOK - thiacin...Meiosis 1. Do you know the significance of meiosis. 2. Do you know how genetic variation occurs during meiosis. 3. Can you compare and contrast mitosis