Introduction to Chapters 9 & 10 Mitosis & Meiosis

Introduction

In this module we begin to consider how organisms reproduce themselves. Here we are interested in

events at the cellular level. Later in the course, we'll look at reproduction from the organism level.

In 1855 Rudolf Virchow, a German physician, stated "Where a cell exists, there must have been a

preexisting cell, just as the animal arises only from an animal and the plant only from a plant." The

perpetuation of life is based on the reproduction of cells. In order for cells to reproduce themselves

accurately they must reproduce the genes they contain, as well as their other structures. The first process

we consider in this module is called mitosis. Technically, this process is the reproduction of genetic

material within a cell, but the term is commonly applied to the entire process of cell division. Our growth

and development as organisms is dependent on mitosis. Some of the cells in our bodies, such as blood

cells, and skin cells, continue dividing throughout our lives. Others, such as muscle and nerve cells, stop

dividing in childhood. This is one reason why, when people get to my age, muscle mass begins to

decrease. Anyway, our first consideration will be the life cycle of a cell (the cell cycle) and mitosis.

The second topic for this week is a process called meiosis. Meiosis is part of a process you may have

heard about called sex. In fact, a stuffy academic definition of sex is: the process of meiosis followed by

the process of fertilization. Meiosis itself is a special type of chromosomal and cell division that results in

formation of specialized sex cells called gametes. Almost all cells in our bodies are somatic cells each

with two sets of chromosomes, one set from each of our parents. In the case of you and I, that is human

beings, there are two sets of 23 chromosomes (46 total) in each of our somatic cells. Meiosis is a type of

cell division resulting in cells that have only one set of chromosomes (23 in humans). These cells are

called gametes. Gametes produced by males are called sperm, gametes produced by females are called

eggs. Eggs and sperm have only one set of chromosomes. When fertilization occurs, a sperm cell delivers

its set of chromosomes to an egg cell thus creating a zygote with two sets of chromosomes, the number

we originally started with. Our second topic for the week, then, is an examination of this process.

Course outcomes:

Describe the processes of DNA replication, mitosis, and meiosis.

Learning goals:

Describe the importance of cell division

Describe how genes are passed from one generation to the next

Describe how DNA is duplicated and sorted accurately into duplicated cells

Describe how cells become different from each other.

Describe what can go wrong during cell division

Assignments:

1. Read chapters 9 and 10 in your text book.

Go to the external links found within the Black Board program and examine the web sites listed.

2. Clearly understand the cell cycle and the four stages of mitosis.

3. Understand cytokinesis and be able to describe this process during mitosis. Describe the

differences between plant and animal cellular cytokinesis.

4. Relate meiosis to mitosis. Which of these conditions occurs when and where.

Web Pages

Mitosis http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html

This site is simple and easy to read. Great over view of subject.

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html

Very good overview site with drawings of the cell cycle. Please note: Questions for the next test will

be drawn from this tutorial.

Plant mitosis http://www.cellsalive.com/mitosis.htm

This animated interactive graphic shows the stages of

mitosis. http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/cell_division.html

Mitotic cells of onion root tip. Note the 400 power view has an example of all four cells in their

various phases of cellular division. You may see any one of these cells on the lab exam.

Examine this web site for the various pictures of the cell cycle both for onion and white cells.

Meiosis..... http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmeiosis.html

This web site is simple and easy to read for a great over view of subject.

http://www.biology.arizona.edu/cell_bio/tutorials/meiosis/main.html

Very good web site to review and understand. Question for the next lecture test will be coming

from this site.

http://www.accessexcellence.org/AB/GG/comeiosis.html

MITOSIS

Chapter 9 Somatic Cell Division

INTRODUCTION:

The continuation of life depends on cell division. Cell division is necessary for the growth, repair,

replacement and maintenance of a living system. This cell division is referred to as mitosis and is

common to both animals and plant life. Mitosis begins human following the fertilization of the human

egg and will continue throughout the life of a human.

EXPECTED OUTCOMES:

1. The key roles of cell division

2. Understand how cell division function in reproduction, repair and maintenance

3. Be able to discuss the process of mitosis at each phase of cell division

4. Master the vocabulary associated with this unit

5. Understand and be able to compare and contrast cytokinesis (the division of cytoplasm)

both for animal and plant cells

REFERENCE:

Starr & Taggart, Pub. Brooks & Cole. 9 ed. Chapter 9. pg. 148 - 159.th

Campbell, Reece & Mitchell. Pub.Addison Wesley Logman, Inc. 5 ed.th

Chapter 12. pg. 206 -238.

I. KEY POINTS

A. Chromosome structure

1. Chromosomes are molecules of DNA complexes with proteins

2. Prior to division

a. Chromosome duplicate

b. Centromere joins sister chromatids

3. Centromere

a. Region where the chromosome will attach to microtubules during nuclear division

II. CELL CYCLE

A. About 90% of the cell’s existence is spent in interphase

11. Interphase: Cell’s mass increases (G ), the DNA double (S) and the cytoplasmic

2 components approximately double in number (G ) .

2. Some stop at interphase never to divide again ---- i.e. Brain cells

III. MITOSIS OVERVIEW

A. Four sequential stages of mitosis and these are:

Prophase, Metaphase, Anaphase, Telophase

B. Spindle apparatus

1. Moves the chromosome

2. Is composed of two sets of microtubules

3. Microtubules, which are components of the cytoskeleton, extend from the two “poles” of the cell during division

IV. MITOSIS AN IN DEPT EXAMINATION

A. Prophase (Mitosis begins)

1. Chromosomes start condensing

a. Chromosomes become visible as rod like units, with two sister chromatids

b. Centromere connect the sister chromatids

1) On the surface of the centromere lies the kinetochore

a) Microtubules of the spindle apparatus connect to the centromere via thekinetochore

2. The spindle apparatus forms

a. Spindle apparatus composed of microtubules

b. Spindles attached to the kinetochore and to the centrioles

1) Centrioles have duplicated by the time prophase is under way

2) Centrioles migrate to opposite ends of the cell

B. Metaphase

1. The nuclear membrane breaks down in the transition between pro- and metaphase

2. Sister chromatids become oriented toward opposite poles

a. Spindle fibers and kinetochores interact to orient chromatids along equatorial region of the cell half way between the poles

C. Anaphase

1. Sister chromatids separate and move toward opposite poles

a. Microtubules attached to kinetochores shorten as chromosomes approach poles

2. Each chormatid is an independent chromosome

D. Telophase

1. Two daughter chromosomes of each pair of chromosomes arrive at opposite poles2. The nuclear envelope reforms from the fusion of small vesicles Mitosis is complete

V. DIFFERENCE BETWEEN ANIMAL AND PLANT CELL DIVISION

A. Plants from cell plate (cellulose) that separates the two new cells

B. Animal cells, contractile microfilaments at the cleavage furrow pulls the plasma membrane inward

MEIOSISCHAPTER 10 Gamete formation

INTRODUCTION

The understanding of the process of Meiosis is very important towards the understanding of chapter 11

and 12 of our text book. Where as Mitosis takes place in somatic cells (body cells) Meiosis takes place in

specialized germ cells of humans. These cells Germ Cells give rise to haploid (a single set of

chromosomes) gamete cells: egg and sperm cells. Like mitosis, meiosis under goes the four phase of cell

division: Prophase, Metaphase, Anaphase and Telophase. However, unlike mitosis, meiosis under goes

two of cellular divisions to only one of mitosis. In this chapter we will examine similarities and

differences between Meiosis and Mitosis. Remember mitosis is somatic cellular division resulting in

exact copies of the parent cell while meiosis results in gametes cells (egg and sperm cells) necessary for

new life.

EXPECTED OUTCOMES:

1. Understand and describe the differences between mitosis and meiosis.

2. Be able to describe how genetic variations arises through the process of meiosis.

3. Know the differences between Oogenesis spermatogenesis

4. Be come familiar with the vocabulary

Reference:

Starr & Taggart, Pub. Brooks & Cole. 9th ed. Chapter 10. pg. 162 - 173.

Campbell, Reece & Mitchell. Pub.Addison Wesley Logman, Inc. 5th ed. Chapter 13. pg. 226 -238

I. OVERVIEW OF MEIOSIS

A. Think "Homologous"

1. Meiosis begins with diploid (2n=46) germ cells and produces haploid gametes(n=23)

a. In 2n cells there are 2 chromosomes of each type. These are called homologous chromosomes. b. Homologous chromosomes line up during meiosis

2. Meiosis produces gametes that have one of each pair of homologous chromosomes

B. Overview of the Two Divisions

1. In some ways meiosis resembles mitosis

a. The chromosomes are duplicated during interphase to form sister chromatids held together at the centromere

b. Chromosomes are moved by the microtubules of the spindle apparatus

2. Unlike mitosis, meiosis has two series of divisions - Meiosis I and II

a. During meiosis I, homologous chromosomes pair and cytokinesis follows 1) Each of the 2 daughter cells receives a haploid (1n) number of chromosomes

2) Each chromosome is still duplicated

b. In meiosis II, the sister chromatids of each chromosomes separate; cytokinesis follows resulting in four haploid cells

II. KEY EVENT DURING MEIOSIS I

A. Prophase I Activities

1. Homologous chromosome pair up in a process called

SYNAPSIS

a. Nonsister chromatids exchange segments in a process called

CROSSING OVER

b. Because alleles for the same trait can vary, new combinations of genes in each

chromosomes can result; this is one source of genetic variation.

2. After crossing over, the nonsister chromatids begin to partially separate but remain attached by

chiasmata

B. Metaphase I Alignments

1. During metaphase I, homologous chromosomes randomly line up at the spindle equator

2. During anaphase I, homologous chromosomes (still duplicated) separate into 2 haploid cells, each of which has a random mix of material and paternal chromosomes

III. FORMATION OF GAMETES

A. Gamete formation in animals

1. The life cycle of multi celled animals proceeds from

meiosis to gamete formation ---> fertilization ---->growth by mitosis

2. In males, meiosis and gamete formation are called

spermatogenesis a. Germ cell (2n) --> primary spermatocyte (2n) ---> Meiosis I ---> two secondary spermatocytes (n) ---> Meiosis II ---> four spermatids (n)

b. Spermatids change in form; each develops a tail to become mature sperm.

3. In females, meiosis and gamete formation are called oogenesis

a. Germ cell (2n) --> primary oocyte (2n) -->

MEIOSIS I secondary oocyte (n, and large in size) plus polar body (n, and small in size)

MEIOSIS II one large ovum (n) plus three polar bodies (n, small) b. the single ovum is the only cell capable of being fertilized by a sperm; the polar bodies wither and die.

IV. GENE SHUFFLING AT FERTILIZATION

A. The diploid chromosome number is restored at fertilization when two very different gamete nuclei fuse to form the zygote.

B. The variation present at fertilization is from three sources:

1. Crossing over occurs during prophase I. 2. Random alignments at metaphase I lead to millions of combinations of maternal and parental chromosomes in each gamete

3. Of all the genetically diverse gametes produced, chance will determine which two will meet.

V. MEIOSIS AND MITOSIS COMPARED

A. Mitotic cell division produces clones; this type of division is common in asexually reproducing organisms and in the growth process.

B. Meiosis occurs only in the germ cells used in sexual reproduction; it gives rise to novel combinations of alleles in offspring

Chapter_9_10_Notes.wpd

Biology 101Chapter 9 Mitosis

Matching

Choose the most appropriate answer for eachterm.1. _____ centromere 2. _____ haploid or n cell 3. _____ diploid or 2n cell 4. _____ chromosome 5. _____ nuclear division 6. _____ germ cells 7. _____ somatic cells 8. _____ sister chromatids 9. _____ mitosis and meiosis 10. _____ chromosome number 11. _____ nucleosomes 12. _____ histones

A. Cell lineage set aside for forming gametes and sexual reproduction

B. Necessary for the reproduction of eukaryotic cells

C. Any cell having two of each type of chromosome characteristic of the species

D. The number of each type of chromosome present in a cell (n or 2n)

F. Each DNA molecule with attached proteinsF. The chromosomal proteinsG. A histone with a spool of DNA around itH. Mechanisms by which cells sort out and

package parent DNA molecules into new cell nuclei

I. A small chromosome region with attachment sites for microtubules

J. The two attached DNA molecules of a duplicated chromosome

K. Body cells that reproduce by mitosis and cytoplasmic division

L. Possess only one of each type of chromosome characteristic of the species

LabelingFor each number in the accompanying figure, identify the appropriate component of the cell cycle.

13. _______14. _______15. _______16. _______17. _______18. _______19. _______20. _______

Matching

Link each time span identified below with the most appropriate number in the preceding Labelingsection.

24. _____ Period after duplication of DNA during which the cell prepares for division

25. _____ The complete period of nuclear division, which is followed by cytoplasmic division

(a separate event)

26. _____ DNA duplication occurs now; a time for “synthesis” of DNA and proteins

27. _____ Period of cell growth before DNA duplication; a “gap” of interphase

28. _____ Usually the longest part of a cell cycle

29. _____ Period of cytoplasmic division

30. _____ Period that includes G1, S. G2

31. _____ Period of nuclear division

Chronological OrderUsing the illustration from the previous page, place the phases of mitosis in their correct chronologicalorder. First, in the parentheses, place the number corresponding to the mitosis diagram. Then place thecorrect name of the stage in the answer blank following. The first step is done as an example. 9. _____interphase_______ ( 1 )

10. ____________________ ( )

11. ____________________ ( )

12. ____________________ ( )

13. ____________________ ( )

14. ____________________ ( )

15. ____________________ ( )

16. ____________________ ( )

Labeling and Matching

Identify each of the mitotic stages shown by entering the correct stage in the blank beneath the sketchbelow. Select from the following: late prophase, transition to metaphase (prometaphase), cell atinterphase, metaphase, early prophase, telophase, interphase—daughter cells, and anaphase. Completethe exercise by matching and entering the letter of the correct phase description in the parenthesesfollowing each label.

A. Attachments between two sister chromatids of each chromosome break; the two are now separate chromosomes that move to opposite spindle poles.

B. Microtubules penetrate the nuclear region and collectively form the spindle apparatus; microtubules become attached to the two sister chromatids of each chromosome.

C. The DNA and its associated proteins have started to condense.D. All the chromosomes are now fully condensed and lined up at the equator of the spindle.F. DNA is duplicated and the cell prepares for nuclear division.F. Two daughter cells have formed, each diploid with two of each type of chromosome, just like the

parent cell’s nucleus.C. Chromosomes continue to condense. New microtubules are assembled, and they move one of two

centriole pairs toward the opposite end of the cell. The nuclear envelope begins to break up.H. Patches of new membrane fuse to form a new nuclear envelope around the decondensing

chromosomes.

Matching

Choose the most appropriate answer for each.

1. _____ S

2. _____ histones

3. _____ nucleosome

4. _____ H1

5. _____ kinetochore

6. _____ centromere

7. _____ metaphase

8. _____ DNA topoisomerase

9. _____ colchicine

10. _____ motor proteins

A. Specific histone that stabilizes the structural array of nucleosomesB. Period of the cell cycle in which the chromosomes are maximally

condensedC. Extend from microtubule surfaces and have roles in chromosome

movementsD. Disk-shaped structure acting as a docking site for spindle

microtubulesE. Chemical that disrupts microtubule formation of cell spindlesF. Period of the synthesis of proteins that become organized into

structural scaffolding for the condensed version of chromosomes

G. An enzyme that supervises the untangling of DNA threads during cell divisions

H. Term for a histone-DNA spoolI. Many act like spools for winding up small stretches of DNAJ. The most prominent constriction of a metaphase chromosome

ChoiceFor questions 1—10 on cytoplasmic division, choose from the following:

a. plant cells b. animal cells

1. ______ Formation of a cell plate

2. _____ Contractions continue and in time will divide the cell in two

3. _____ Cellulose deposits form a cross wall between the two daughter cells

4. _____ Possess rigid walls that cannot be pinched in two

5. _____ A cleavage furrow

6. _____ Deposits form a cementing middle lamella

7. _____ A band of microfilaments beneath the cell’s plasma membrane generates the force for

cytoplasmic division

8. _____ Two daughter nuclei are cut off in separate cells, each with its own cytoplasm and plasma

membrane

9. _____ At the location of a disklike structure, deposits of cellulose accumulate

10. _____ The structure grows at its margins until it fuses with the parent cell’s plasma membrane

Self-Quiz

_____ 1. The replication of DNA occursa between the growth phases of inter- phaseb. immediately before prophase of mitosisc. during prophase of mitosis d. during prophase of meiosis

______ 2. In the cell life cycle of a particular cell,

a. mitosis occurs immediately prior to G1b. G2 precedes Sc. G1 precedes Sd. mitosis and S precede G1

_____ 3. Diploid refers toa. having two chromosomes of each type insomatic cellsb. twice the parental chromosome numberc. half the parental chromosome numberd. having one chromosome of each type insomatic cells

______ 4. Somatic cells are cells;germ cells are ____________________ cells.

a. meiotic; body b. body; body c. meiotic; meiotic d. body; meiotic

_____ 5. If a parent cell has 16 chromosomes andundergoes mitosis, the resulting cells wall have __________________ chromosomes. a. 64b. 32c. 16d. 8e. 4_____ 6. Which of the following terms identifiesa constricted region on the chromosome to whichmicrotubules bind during cell division? a. sister chromatidsb. nucleosome c. centromere d. diploid e. cell membrane

7. The correct order of the stages of mitosis isa. prophase, metaphase, telophase, anaphaseb. telophase, anaphase, metaphase, prophasec. telophase, prophase, metaphase, anaphased. anaphase, prophase, telophase, metaphasee. prophase, metaphase, anaphase, telophase

8. ‘The nuclear envelope brealcs up completelyinto vesicles. Microtubules are now free tointeract with the chromosomes.” These sentencesdescribe the of mitosis.a. prophaseb. metaphasec. transition to metaphased. anaphasee. telophase

9. During ______, sister chromatids of eachchromosome are separated from each other, andthose former partners, now chromosomes, aremoved toward opposite poles.a. prophaseb. metaphasec. anaphased. telophase

10. Each histone-DNA spool is a single structuralunit called aa. kinetochoreb. motor proteinc. DNA topoisomerased. nucleosome

11. In the process of cytokinesis, cleavagefurrows are associated with cell division, and cellplate formation is associatedwith cell division.a. animal; animalb. plant; animalc. plant; plantd. animal; plant

Biology 101Chapter 10 Meiosis

Write out and understand these terms

germ cells _______________________________________________________________________________________________________________________________________________________________

gametes _______________________________________________________________________________________________________________________________________________________________

asexual reproduction_______________________________________________________________________________________________________________________________________________________________

genes _______________________________________________________________________________________________________________________________________________________________

sexual reproduction_______________________________________________________________________________________________________________________________________________________________

allele _______________________________________________________________________________________________________________________________________________________________

meiosis _______________________________________________________________________________________________________________________________________________________________

chromosome number_______________________________________________________________________________________________________________________________________________________________

diploid number (2n) -_______________________________________________________________________________________________________________________________________________________________

homologous chromosomes_______________________________________________________________________________________________________________________________________________________________

haploid number (n)_______________________________________________________________________________________________________________________________________________________________

sister chromatids_______________________________________________________________________________________________________________________________________________________________

Matching

To review the major stages of meiosis, match the following written descriptions with the appropriatesketch. Assume that the cell in this model initially has only one pair of homologous chromosomes (onefrom a paternal source and one from a maternal source) and crossing over does not occur. Complete theexercise by indicating the diploid (2n = 2) or haploid (n = 1) chromosome number of the cell chosen inthe parentheses following each blank.

1. _______ ( )

2. _______ ( ) 3. _______ ( )

4. _______ ( )

5. _______ ( )

A pair of homologous chromosomes prior to S of interphase in a diploid germ cell

While the germ cell is in S of interphase, chromosomes are duplicated throughDNA replication; the two sister chromatids are attached at the centromere

During meiosis I, each duplicated chromosome lines up with its partner,homologue to homologue

Also during meiosis I, the chromosome partners separate from each other inanaphase 1; cytokinesis occurs, and each chromosome goes to a different cell

During meiosis II (in two cells), the sister chromatids of each chromosome areseparated from each other; four haploid nuclei form; cytokinesis results in fourcells (potential gametes)

Choice

For questions 1—10, choose from the following:a. asexual reproduction b. sexual reproduction

1. _____2. _____3. _____4. _____5. _____6. _____7. _____8. _____9. _____10. _____

Offspring inherit new combinations of alleles One parent alone produces offspring Each offspring inherits the same number and kinds of genes as its parent Commonly involves two parents The production of “clones” Involves meiosis, formation of gametes, and fertilization Offspring are genetically identical copies of the parent Produces the variation in traits that is the foundation of evolutionary change Change can only occur by mutations Offspring inherit new combinations of alleles, which lead to variations in the details oftheir traits

Dichotomous Choice

Circle one of two possible answers given between parentheses in each statement.

11. (Meiosis/ Mitosis) divides chromosomes into separate parcels not once but twice prior to

cell division.

12. Sperm and eggs are sex cells known as (germ/gamete) cells.

13. (Haploid/Diploid) cells possess pairs of homologous chromosomes.

14. (Haploid/Diploid) germ cells produce haploid gametes.

15. (Meiosis/ Mitosis) produces cells that have one member of each pair of homologous

chromosomes possessed by the species.

16. Identical alleles are found on (homologous chromosomes/sister chromatids).

17. Two attached DNA molecules are known as (sister chromatids/homologous chromosomes).

18. Two attached sister chromatids represent (one/two) chromosome(s).

19. One pair of duplicated chromosomes would be composed of (two/four) chromatids.

20. With meiosis, chromosomes proceed through (one/two) divisions to yield four haploid nuclei.

21. During meiosis I, each duplicated (chromosome/chromatid) lines up with its partner,

homologue to homologue, and then the partners are moved apart from one another.

22. Cytoplasmic division following meiosis II results in four (diploid/haploid) cells.

23. During (meiosis I/meiosis II), the two sister chromatids of each chromosome are separated

from each other; each sister chromatid is now a chromosome in its own right.

24. If human body cell nuclei contain 23 pairs of homologous chromosomes, each resulting

gamete will contain (23/46) chromosomes.

Labeling and Matching

Identify each of the meiotic stages shown on the opposite page by entering the correct stage of eithermeiosis I or meiosis II in the blank beneath the sketch. Choose from the following: prophase I, metaphaseI, anaphase I, telophase I, prophase II, metaphase II, anaphase II, and telophase II. Complete the exerciseby matching and entering the letter of the correct stage description in the parentheses following eachlabel.

A. The spindle is now fully formed; all chromosomes are positioned midway between the poles of one cell.

B. In each of two daughter cells, microtubules attach to the kinetochores of chromosomes, and motor proteins drive the movement of chromosomes toward the spindle’s equator.

C. Four daughter nuclei form; when the cytoplasm divides, each new cell has a haploid chromosome number, all in the unduplicated state; the cells may develop into gametes in

animals or spores in plants.D. In one cell, each duplicated chromosome is pulled away from its homologous partner; the

partners are moved to opposite spindle poles.E. Duplicated chromosomes condense; each chromosome pairs with its homologous partner;

crossing over and genetic recombination (swapping of gene segments) occur; each chromosome becomes attached to some microtubules of a newly forming spindle.F. Motor proteins and spindle microtubule interactions have moved all the duplicated

chromosomes so that they are positioned at the spindle equator, midway between the poles.C. Two haploid cells form, each having one of each type of chromosome that was present

in the parent cell; the chromosomes are still in the duplicated state.H. Attachment between the two chromatids of each chromosome breaks; former

“sister chromatids” are now chromosomes in their own right and are moved to opposite poles by motor proteins.

ChoiceFor questions 1—14, choose from the following:

a. animal life cycle b. plant life cycle c. both animal and plant life cycles

1. _____2. _____3. _____4. _____5. _____6. _____7. _____8. _____9. _____

10. _____11. ____12. _____13. ____14. _____

Meiosis results in the production of haploid spores. A zygote divides by mitosis. Meiosis results in the production of haploid gametes. Haploid gametes fuse in fertilization to form a diploid zygote. A zygote divides by mitosis to form a diploid spore-producing body (sporophyte). During meiosis, one egg and three polar bodies form. A spore divides by mitosis to produce a haploid gamete-producing body (gametophyte). Gametes form by oogenesis and spermatogenesis. A haploid gamete-producing body (gametophyte) divides by mitosis to produce haploidgametes. A secondary oocyte gets nearly all the cytoplasm. A haploid spore divides by mitosis to produce a gamete-producing body (gametophyte). A diploid body forms from mitosis of a zygote.A gamete-producing body and a spore-producing body develop during the life cycle. One daughter cell of the secondary oocyte develops into a second polar body.

Matching

Choose the most appropriate answer for each.

14. ____ 223

15. ____ paternal chromosomes

16.____ early prophase I

17. ____ nonsister chromatids

18.____ late prophase I

19. ____ crossing over

20.____ metaphase I

21. ____ synapsis

22. ____ function of meiosis

23. ____ maternal chromosomes

A. Random positioning of maternal and paternal chromosomes at the spindle equator

B. Chromosomes condense and become thicker rodlike formsC. Reduction of the chromosome number by half for forth

coming gametesD. Break at the same places along their length and then

exchange corresponding segmentsE. Twenty-three chromosomes inherited from your motherF. Combinations of maternal and paternal chromosomes

possible in gametes from one germ cellC. Each duplicated chromosome is in threadlike formH. An intimate parallel array of homologues that favors

crossing overI. Twenty-three chromosomes inherited from your fatherJ. Breaks up old combinations of alleles and puts new

ones together in pairs of homologous chromosomes

Complete the Table

1. Complete the following table by entering the word mitosis or the word meiosis in the blank adjacent tothe statement describing one of these processes.

Description Mitosis/Meiosis

a. Involves one division cycle

b. Functions in growth and tissue repair

c. Daughter cells are haploid

d. Occurs only in germ cells

e. Involves two division cycles

f. Daughter cells have one chromosome from each homologous pair

g. Introduces variation in traits among the offspring

h. Daughter cells have the diploid chromosome number

i. Completed when four daughter cells are formed

j. Produces clones

k. Involves the process of crossing over

Matching

The cell model used in this exercise has two pairs of homologous chromosomes, one long pair and oneshort pair. Match the descriptions to the numbers of chromosomes shown in the following sketches.

2. _____3. _____4. _____5. _____6. _____7. _____

one cell at the beginning of meiosis II a daughter cell at the end of meiosis II metaphase I of meiosis metaphase of mitosis G1 in a daughter cell after mitosis prophase of mitosis

Short Answer

The following questions refer to the sketches above; enter your answer in the blank following eachquestion.

8.9.10.11.12.

How many chromosomes are present in cell F? __________How many chromatids are present in cell F? ____________How many chromatids are present in cell C? ___________How many chromatids are present in cell D? ___________How many chromosomes are present in cell F? ___________

Self-Quiz

_____ 1. Which of the following does not occurin prophase I of meiosis?

a. a cytoplasmic divisionb. a cluster of four chromatidsc. homologues pairing tightlyd. crossing over

____ 2. Crossing over is one of the most important events in meiosis because

a. it establishes new genetic combinations not present in the parents

b. homologous chromosomes must be separated into different daughter cells

c. the number of chromosomes allotted to each daughter cell must be halved

d. it sorts the chromatids into gametes for fertilization

_____ 3. Crossing over a. generally results in pairing of homologues

and binary fissionb. is accompanied by gene-copying eventsc. involves breakages and exchanges between

sister chromatidsd. is a molecular interaction between two of

the nonsister chromatids of a pair of homologous chromosomes

_____ 4. If an organism has a chromosome number of 5, how many different combinationsof homologous chromosomes are possible atmetaphase 1?a. 2b. 52c. 5d. 10

____ 5. Which of the following does not increasegenetic variation? a. crossing overb. random fertilizationc. prophase of mitosisd. random homologue alignments at metaphase I

_____ 6. Which of the following is the most correct sequence of events in animal life cycles? a. meiosis — fertilization — gametes — diploid

organismb. diploid organism—meiosis—

gametes—fertilizationc. fertilization—gametes— diploid

organism—meiosisd. diploid organism—fertilization— meiosis —

gametes

_____ 7. In sexually reproducing organisms, thezygote is _______________ .a. an exact genetic copy of the female parentb. an exact genetic copy of the male parentc. completely unlike either parent geneticallyd. a genetic mixture of male and female parents

_____ 8. Which of the following is the mostcorrect sequence of events in plant life cycles?a. fertilization—> zygote—> sporophyte—>

meiosis —> spores —> gametophytes —>gametes

b. fertilization —> sporophyte —> zygote—>meiosis —> spores—> gametophytes —>gametes

c. fertilization —> zygote —> sporophyte —>meiosis —> gametes —> gametophyte —>spores

d. fertilization —> zygote —> gametophyte —>meiosis —> gametes —> sporophyte —>spores

_____ 9. While observing a given cell under amicroscope, you notice that pairs of condensedhomologous chromosomes appear to be aligningin the center of the cell. The most likely stage ofmeiosis for this cell is ___________________a. anaphase II b. metaphase II c. metaphase I d. prophase II e. telophase I