Cellular Processes 13 - BIOLOGY JUNCTION

Mitosis Activity

Stages of Mitosis

Introduction

Mitosis, also called karyokinesis, is division of the nucleus and its chromosomes. It is followed by division of the cytoplasm known as cytokinesis. Both mitosis and cytokinesis are parts of the life of a cell called the Cell Cycle. Most of the life of a cell is spent in a non-dividing phase called Interphase. Interphase includes G1 stage in which the newly divided cells grow in size, S stage in which the number of chromosomes is doubled and appear as chromatin, and G2 stage where the cell makes the enzymes & other cellular materials needed for mitosis.

Mitosis has 4 major stages — Prophase, Metaphase, Anaphase, and Telophase. When a living organism needs new cells to repair damage, grow, or just maintain its condition, cells undergo mitosis.

During Prophase, the DNA and proteins start to condense. The two centrioles move toward the opposite end of the cell in animals or microtubules are assembled in plants to form a spindle. The nuclear envelope and nucleolus also start to break up.

Prophase

During Metaphase, the spindle apparatus attaches to sister chromatids of each chromosome. All the chromosomes are line up at the equator of the spindle. They are now in their most tightly condensed form.

Metaphase

During Anaphase, the spindle fibers attached to the two sister chromatids of each chromosome contract and separate chromosomes which move to opposite poles of the cell.

Anaphase

In Telophase, as the 2 new cells pinch in half (animal cells) or a cell plate forms (plant cells), the chromosomes become less condensed again and reappear as chromatin. New membrane forms nuclear envelopes and the nucleolus is reformed.

Telophase

Objective:

In this lab, you will determine the approximate time it takes for a cell to pass through each of the four stages of mitosis. You may use your textbook and class notes to help you identify the stages of mitosis as seen under the microscope.

Materials:

Microscope, prepared slide onion root tip or whitefish blastula, textbook, lab worksheet, pencil

Procedure:

Set up a compound light microscope and turn on the light.
Place a slide containing a stained preparation of the Allium (onion root tip) or Whitefish blastula.
Locate the meristematic or growth zone, which is just above the root cap at the very end of the tip or
Focus in on low power, and then switch to medium or high power. Below find micrographs of the four stages of mitosis. Use them to help you identify the stages on the microscope slide.

Prophase (onion)

Metaphase (onion)

Anaphase (onion)

Telophase (whitefish)

Now count the number of cells found in each stage of mitosis and place the data in the chart below.
Determine the percentage of time each cell will spend in each stage of mitosis. Divide the number of each cell by the total number of cells and multiply by 100 to determine the percentage. Place these values in the chart below.

Stage of Mitosis	Number of Cells	Percent of time in each stage = # of cells in stage X 100% Total # of Cell
Prophase		%
Metaphase		%
Anaphase		%
Telophase		%
Interphase (Not a Mitotic Stage)		%
Total # cells		100%

Line graph the data you have just collected. Be sure to label the X and Y axis & include the units of measurement.

Title: __________________________________________________

Graph Legend:

Questions:

1. Of the four stages of mitosis, which one takes the most time to complete?

2. Which is the shortest stage in duration?

3. What would happen if the process of mitosis skipped metaphase? telophase?

Further Study:

Normal Cell Division may be observed in onion root tips. Many of the processes are similar to those in animal cells. However, in plant cells, the cell plate between daughter cells forms from the Golgi.

Find all of the stages of mitosis and interphase in the above picture. Make a sketch of each stage and briefly describe what is occurring. Count and record the number of cells you see in each stage.

	Projects
	Notes

Mitosis and Meiosis

Mitosis and Meiosis

Introduction
All new cells come from previously existing cells. New cells are formed by the process of cell division which involves both replication of the cell’s nucleus (karyokinesis) and division of the cytoplasm( cytokinesis).

There are two types of nuclear division: mitosis and meiosis. Mitosis typically results in new somatic (body ) cells. Formation of an adult organism from a fertilized egg, asexual reproduction, regeneration, and maintenance or repair of body parts are accomplished through mitotic cell division. Meiosis results in the formation of either gametes (in animals) or spores ( in plants). These cells have half the chromosome number of the parent cell. You will study meiosis in Exercise 3B. Where does one find cells undergoing meiosis? Plants and animals differ in this respect. In higher plants the process of forming new cells is restricted to special growing regions called meristems. These regions usually occur at the tips of stems or roots. In animals, cell division occurs anywhere new cells are formed or as new cells replace old ones. However, some tissues in both plant and animals rarely divide once the organism is mature.

Exercise 3A.1: Observing Mitosis in Plant and Animal Cells Using Prepared Slides of the Onion Root Tip and Whitefish Blastula

Figure 3.1 Close up view of different stages of mitosis in an onion root tip:

Figure 3.2 Whitefish Blastula

Procedure:
Examine prepared slides of either onion root tips or whitefish blastula. Locate the meristematic region of the onion, or locate the blastula with 10X objective, and then use the 40X objective to study individual cells. Identify one cell which clearly represents each phase of mitosis. Sketch and label the cell in the box provided.

1. The non dividing cell is in a stage called interphase. The nucleus may have one or more dark-stained nucleoli and is filled with a fine network of threads, the chromatin. During interphase, DNA replication occurs.

Interphase

2. The first signs of cell division occurs in prophase. There is a thickening of the chromatin threads, which will continue until it is evident that the chromatin has condensed into chromosomes. With somewhat higher magnification you may be able to see the two chromatids held together by the centromere. As prophase continues , the chromatids continue to thicken and shorten. The nuclear envelope disappears and the beginnings of the spindle apparatus begin to appear.

Prophase

3. At metaphase, the chromosome pairs have moved to the center of the spindle. One particular part of each chromosome, the centromere, attaches to the spindle. The centromeres of all the chromosomes lie about the same level of the spindle called the metaphase plate.

Metaphase

4. At the beginning of anaphase, the centromere regions of each pair of chromatids separate and are moved by the spindle fibers toward opposite poles of the spindle, dragging the rest of the chromatid behind them. Once each chromatid is separate it is called a chromosome.

Anaphase

5. Telophase, the last stage of division, is marked by a pronounced condensation of the chromosomes, followed by the formation of a new nuclear envelope around each group of chromosomes. The chromosomes gradually uncoil into the fine threads of chromatin, and the nucleoli reappears. Cytokinesis may occur. This is the division of the cytoplasm into two new cells. In plants, a new cell wall is laid down between the daughter cells. In animal cells, the old cells will pinch off in the middle along a cleavage furrow to form two new daughter cells.

Telophase

Analysis Questions:
1. Why is it more accurate to call mitosis “nuclear replication” rather than “cellular division”?

_____________________________________________________________________

2. Explain why the whitefish blastula and onion root tip are selected for study of mitosis.

_____________________________________________________________________

Exercise 3A.2: Time for Cell Replication
Procedure:
It is hard to imagine that you can estimate how much time a cell spends in each phase of cell replication from a slide of dead cells. Yet this is precisely what you are going to do in this part of the lab. Since you are working with a prepared slide, you cannot get any information about how long it takes a cell to divide. What you can determine is how many cells are in each phase. From this, you can infer the percent of time each cell spends in each phase.

1. Observe every cell in one high power field of view and determine which phase of the cell cycle it is in. This is best done in pairs. The partner observing the slide calls out the phase of each cell while the other partner records. Then switch so the recorder becomes the observer and visa versa. Count at least two full fields of view. If you have not counted 200 cells, then count a third field of view.

2. Record your data in Table 3.1.

Table 3.1

	Number of Cells				Percent of Total Cells Counted	Time in Each Stage
	Field 1	Field 2	Field 3	Total
Interphase
Prophase
Metaphase
Anaphase
Telophase
Total Cells Counted

3. Calculate the percentage of cells in each phase.

Consider it takes, on average, 24 hours (or 1,440 minutes) for onion root-tip cells to complete the cell cycle. You can calculate the amount of time spent in each phase of the cell cycle from the percent of cells in that stage.

Percent of cells in stage X 1,440 minutes = ___________ minutes of cell cycle spent in stage.

Questions:
1. If your observations had not been restricted to the area of the root tip that is actively dividing, how would your results have been different?

_____________________________________________________________________

2. Based on the data in Table 3.1, what can you infer about the relative length of time an onion root-tip cell spends in each stage of cell division?

_____________________________________________________________________

Mitosis PPT Questions

Cell Cycle and Mitosis
ppt Questions

Cell Cycle

1.Prokaryotic organisms include ___________, while plants and animals are ____________.

2. Describe prokaryotes.

3. How do bacteria asexually reproduce?

4. Name the 3 main steps of binary fission in bacteria.

5. Name a bacterial cell that reproduces by binary fission.

6. Describe eukaryotes.

7. How do eukaryotes asexually reproduce cells?

8. The stages in the growth and reproduction of a cell are called the __________ ___________.

9. List the 5 stages in the cell cycle.

10. What does G1 stage stand for?

11. Name two things that happen to a cell during G1?

12. What is the S stage of the cell cycle?

13. _________ instructions are copied in the S phase as ___________ are duplicated.

14. _______ stands for second growth stage.

15. G2 is the time between ____________ and ___________.

16. Cells continue to _________ during G2 and to make __________ that will be needed for mitosis or cell division.

17. Mitosis or cell division is known as the ________ stage.

18. How does a cell use its energy during the M phase?

19. Does a cell continue growing & making proteins in the M phase?

20. Mitosis is also called _______________ which means division of the ____________.

21. ____________ is called the resting stage and makes up the longest part of a cell’s life cycle.

22. What happens to cells during interphase?

23. Are chromosomes visible during interphase?

Mitosis

24. Name the 4 stages of mitosis.

25. Name 2 things that happen to a cell during prophase.

26. Can chromosomes be seen during prophase?

27. Sketch a eukaryotic chromosome and label the centromere and kinetochore fiber that attaches to it.

28. How many pairs of chromosomes are found in humans?

29. List 3 things that occur during metaphase.

30. Where are chromosomes located during metaphase of a cell?

31. What stage occurs after metaphase?

32. List 2 things that happen to cells during anaphase.

33. Sketch and label the mitotic spindle and attached chromosomes.

34. What is the last stage of mitosis?

35. Where are the two sets of chromosomes located at Telophase?

36. What two things reform during Telophase?

37. Chromosomes ___________ during Telophase so they are no longer visible.

38. In plants, what begins to form that will separate the two cells?

39. How are the two cells separated from each other in animals?

40. _____________ or division of the cytoplasm follows ___________, division of the nucleus, and forms ____________ daughter cells.

41. How do the two, new daughter cells compare to each other?

42. Label the following stages of mitosis.

Printable Copy

Meiosis Labeling

Meiosis

On each of the images, label the phase of meiosis

1. _______________	2. _______________	3. _______________
4. _______________	5. _______________	6. _______________
7. _______________	8._______________	9._______________
10. _______________	11. A cell with a diploid number of 20 undergoes meiosis. This will produce ________ daughter cells, each with ________ chromosomes. 12. Synapsis occurs during this phase: _______________________ 13 How many different possible combinations are there for a cell that has 10 chromosomes (5 pairs): _____________ 14. Tetrads line up along the equator during this phase: ______________ 15. At the end of meiosis I, ________ daughter cells are created. These daughter cells are [ diploid \| haploid ]. 16. Meiosis occurs in what type of cells: ____________________________

Now label the photographs.
17. _______________	18. _______________	19. _____________
20. _______________	21. _______________	22. _____________
23. _______________	24. _______________	24. _____________
25. _______________

Genetics


1862	1868	1880

Genetic Terminology:

Trait – any characteristic that can be passed from parent to offspring
Heredity – passing of traits from parent to offspring
Genetics – study of heredity
Alleles – two forms of a gene (dominant & recessive)
Dominant – stronger of two genes expressed in the hybrid; represented by a capital letter (R)
Recessive – gene that shows up less often in a cross; represented by a lowercase letter (r)
Genotype – gene combination for a trait (e.g. RR, Rr, rr)
Phenotype – the physical feature resulting from a genotype (e.g. tall, short)
Homozygous genotype – gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr); also called pure
Heterozygous genotype – gene combination of one dominant & one recessive allele (e.g. Rr); also called hybrid
Monohybrid cross – cross involving a single trait
Dihybrid cross – cross involving two traits
Punnett Square – used to solve genetics problems

Blending Concept of Inheritance:

Accepted before Mendel’s experiments
Theory stated that offspring would have traits intermediate between those of its parents such as red & white flowers producing pink
The appearance of red or white flowers again was consider instability in genetic material
Blending theory was of no help to Charles Darwin’s theory of evolution
Blending theory did not account for variation and could not explain species diversity
Particulate theory of Inheritance, proposed by Mendel, accounted for variation in a population generation after generation
Mendel’s work was unrecognized until 1900

Gregor Mendel:

Austrian monk
Studied science & math at the University of Vienna
Formulated the laws of heredity in the early 1860’s
Did a statistical study of traits in garden peas over an eight year period

drawing of a flower cross-section showing both male and female sexual structures

Why peas, Pisum sativum?

Can be grown in a small area
Produce lots of offspring
Produce pure plants when allowed to self-pollinate several generations
Can be artificially cross-pollinate

Picture of Pisum sativum
GARDEN PEA

Mendel’s Experiments:

Mendel studied simple traits from 22 varieties of pea plants (seed color & shape, pod color & shape, etc.)
Mendel traced the inheritance of individual traits & kept careful records of numbers of offspring
He used his math principles of probability to interpret results
Mendel studied pea traits, each of which had a dominant & a recessive form (alleles)
The dominant (shows up most often) gene or allele is represented with a capital letter, & the recessive gene with a lower case of that same letter (e.g. B, b)
Mendel’s traits included:

         a. Seed shape — Round (R) or Wrinkled (r)
            b. Seed Color —- Yellow (Y) or Green (y)
            c. Pod Shape — Smooth (S) or wrinkled (s)
            d. Pod Color — Green (G) or Yellow (g)
            e. Seed Coat Color — Gray (G) or White (g)
            f. Flower position — Axial (A) or Terminal (a)
            g. Plant Height — Tall (T) or Short (t)
            h. Flower color — Purple (P) or white (p)

Mendel produced pure strains by allowing the plants to self-pollinate for several generations
These strains were called the Parental generation or P1 strain

Mendel cross-pollinated two strains and tracked each trait through two
generations (e.g. TT x tt )

Trait – plant height
Alleles – T tall, t short
P1 cross TT x tt			genotype — Tt
	t	t	phenotype — Tall
T	Tt	Tt	genotypic ratio –all alike
T	Tt	Tt	phenotypic ratio- all alike

The offspring of this cross were all hybrids showing only the dominant trait & were called the First Filial or F1 generation
Mendel then crossed two of his F1 plants and tracked their traits; known as an F1 cross

Trait – plant height
Alleles – T tall, t short
F1 cross Tt x Tt			genotype — TT, Tt, tt
	T	t	phenotype — Tall & short
T	TT	Tt	genotypic ratio —1:2:1
t	Tt	tt	phenotypic ratio- 3:1

When 2 hybrids were crossed, 75% (3/4) of the offspring showed the dominant trait & 25% (1/4) showed the recessive trait; always a 3:1 ratio
The offspring of this cross were called the F2 generation
Mendel then crossed a pure & a hybrid from his F2 generation; known as an F2 or test cross

Trait – Plant Height
Alleles – T tall, t short
F2 cross TT x Tt			F2 cross tt x Tt
	T	t		T	t
T	TT	Tt	t	Tt	tt
T	TT	Tt	t	Tt	tt

genotype – TT, Tt			genotype – tt, Tt
phenotype – Tall			phenotype – Tall & short
genotypic ratio – 1:1			genotypic ratio – 1:1
phenotypic ratio – all alike			phenotypic ratio – 1:1

50% (1/2) of the offspring in a test cross showed the same genotype of one parent & the other 50% showed the genotype of the other parent; always a 1:1 ratio

Problems: Work the P1, F1, and both F2 crosses for all of the other pea plant traits & be sure to include genotypes, phenotypes, genotypic & phenotypic ratios.

Mendel also crossed plants that differed in two characteristics (Dihybrid Crosses)
such as seed shape & seed color
In the P1 cross, RRYY x rryy, all of the F1 offspring showed only the dominant form for both traits; all hybrids, RrYy

Traits: Seed Shape & Seed Color
Alleles: R round Y yellow r wrinkled y green
P1 Cross: RRYY x r r yy
	ry	Genotype:	RrYy
RY	RrYy	Phenotype:	Round yellow seed
Genotypic ratio:	All alike
		Phenotypic ratio:	All Alike

When Mendel crossed 2 hybrid plants (F1 cross), he got the following results

Traits: Seed Shape & Seed Color
Alleles: R round Y yellow r wrinkled y green
F1 Cross: RrYy x RrYy
	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYY	RrYy	r rYY	r rYy
ry	RrYy	Rryy	r rYy	r ryy

Genotypes	Genotypic Ratios	Phenotypes	Phenotypic Ratios
RRYY	1	Round yellow seed	9
RRYy	2
RrYY	2
RrYy	4
RRyy	1	Round green seed	3
Rryy	2
r rYY	1	Wrinkled yellow seed	3
r rYy	2
r ryy	1	Wrinkled green seed	1

Problems: Choose two other pea plant traits and work the P1 and F1 dihybrid crosses. Be sure to show the trait, alleles, genotypes, phenotypes, and all ratios.

Results of Mendel’s Experiments:

Inheritable factors or genes are responsible for all heritable characteristics
Phenotype is based on Genotype
Each trait is based on two genes, one from the mother and the other from the father
True-breeding individuals are homozygous ( both alleles) are the same
Law of Dominance states that when different alleles for a characteristic are inherited (heterozygous), the trait of only one (the dominant one) will be expressed. The recessive trait’s phenotype only appears in true-breeding (homozygous) individuals

Trait: Pod Color
Genotypes:	Phenotype:
GG	Green Pod
Gg	Green Pod
gg	Yellow Pod

Law of Segregation states that each genetic trait is produced by a pair of alleles which separate (segregate) during reproduction

Rr
R	r

Law of Independent Assortment states that each factor (gene) is distributed (assorted) randomly and independently of one another in the formation of gametes

RrYy

RY	Ry	rY	ry

Other Patterns of Inheritance:

Incomplete dominance occurs in the heterozygous or hybrid genotype where the 2 alleles blend to give a different phenotype
Flower color in snapdragons shows incomplete dominance whenever a red flower is crossed with a white flower to produce pink flowers

In some populations, multiple alleles (3 or more) may determine a trait such as in ABO Blood type
Alleles A & B are dominant, while O is recessive

Genotype	Phenotype
IOIO	Type O
IAIO	Type A
IAIA	Type A
IBIO	Type B
IBIB	Type B
IAIB	Type AB

Polygenic inheritance occurs whenever many variations in the resulting phenotypes such as in hair, skin, & eye color
The expression of a gene is also influenced by environmental factors (example: seasonal change in fur color)

Trait – plant height

Trait – plant height