Lab Report 11 - Cellular Reproduction & PCR

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Lab Report 11 – Cellular Reproduction

Section I - Concept

The Cell Cycle

The cell cycle describes the different stages that all cells go through

during their life span. The two main parts of the cell cycle are Interphase and

M phase.

Interphase is the stage where the cell performs its normal functions.

Interphase itself can be divided into three stages; G1, S and G2 phases.

1. G1 (G=gap) is where most cells spend the majority of their life and

perform their normal function. And it is at this stage that the cell will

get the signal to divide. The cell grows larger and various organelles

are copied.

2. S phase (S=synthesis) is when the DNA is copied. It is essential that

cells make an exact copy of their chromosomes so that the daughter

cells can function normally. It is during this phase that each

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chromosome is copied and these two sister chromatids are held

together at the centromere.

3. Once the DNA is successfully copied the cell enters G2 phase. It is at

this time that the rest of the cell prepares for cell division and

proteins needed for cell division are synthesized.

M phase (M=mitosis) is the second part of the cell cycle. The results of M

phase are daughter cells, both of which will enter interphase beginning the

cycle over again.

Mitosis

Mitosis is asexual cell division which involves one parent cell dividing

into two identical daughter cells that have the same number of chromosomes.

This process involves four stages; prophase, metaphase, anaphase and

telophase.

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1. Prophase is the first stage of mitosis and involves the disappearance

of the nucleolus, condensation of the chromosomes and the

breakdown of the nuclear membrane. Also during this time, the

centrosomes begin to move to opposite poles of the cell.

2. Metaphase is the second stage and is characterized by the

chromosomes lining up along a central axis. This is the axis where

the actual cell division will take place. The spindle fibers which

attach to the chromosomes at the centromere are often visible during

this stage.

3. Anaphase is the stage where the centromere split and the spindle

fibers pull the sister chromatids apart.

4. Telophase in many ways is the reverse of prophase. The nuclear

membrane begins to reform, chromosomes unwind and the nucleoli

become visible. Two nuclei are forming at opposite sides of the cell.

5. At the very end of telophase, Cytokinesis occurs. Cytokinesis is the

division of the cell itself. Animal cells do this by pinching off at the

axis where the chromosomes lined up during metaphase. Plant cells

build a cell plate between the newly formed nuclei.

Meiosis

Meiosis is a special type of cell division that generates gametes.

Gametes are the cells that are used during sexual reproduction. In humans

the gametes are the eggs and the sperm. Organisms that reproduce sexually,

go through a cycle involving diploid (two copies of every chromosome) cells

forming haploid (one copy of each chromosome) gametes that fuse together to

form a new diploid organism.

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Meiosis involves two rounds of cell division, resulting in the formation of

haploid cells from diploid cells. Like mitosis, each chromosome is copied,

resulting in two identical sister chromatids. Then the process of cell division

begins with Meiosis I followed by Meiosis II.

Meiosis I – Homologous Chromosomes Separate

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Prophase I is characterized by the formation of tetrads. Tetrads are the

pairs of homologous chromosomes (chromosomes that have similar structure

and contain similar genes) including their sister chromatids. During prophase

I, a process called crossing over can occur. Crossing over involves the

exchange of genetic material between two homologous chromosomes resulting

in new genetic combinations that increase variability.

During metaphase I, the tetrads line up along a central axis and

anaphase I is characterized by the separation of homologous chromosomes.

Lastly, telophase I occurs usually resulting in two cells. Both of these cells will

enter meiosis II.

Meiosis II – Sister Chromatids Separate

Meiosis II is very similar to the process of mitosis. During metaphase II the

remaining chromosomes line up along the central axis. During anaphase II the

sister chromatids split and move to opposite sides of the cell. Lastly, the end result

of telophase II is the formation of haploid gametes.

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Karyotypes

A karyotype is the display of an individual’s chromosomes as they appear

during metaphase. In normal humans there are 23 pairs of chromosomes. Each

human has 22 pairs of autosomes. These pairs are homologous because they have

similar shapes and banding patterns. In addition to the autosomes, each human

has a pair of sex chromosomes, which determine gender. Two copies of the X

chromosome results in a female, while one X and one Y chromosome results in a

male.

Non-Disjunction

Sometimes during gamete formation, non-disjunction can occur. Non-

disjunction is when the chromosomes fail to separate during either anaphase I or II.

This will result in a gamete with an abnormal number of chromosomes. If one of

these gametes is involved in fertilization, then the resulting individual will have an

abnormal number of chromosomes. Often this situation leads to a syndrome, a

specific set of characteristics.

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A table of syndromes associated with abnormal chromosome numbers is included

below.

Syndrome Chromosome number Genetic Make-up

Down’s Syndrome 47 Trisomy 21

Edward’s Syndrome 47 Trisomy 18

Patau’s Syndrome 47 Trisomy 13

Klinefelter’s Syndrome 47 XXY

Turner’s Syndrome 45 Only one X

XYY Syndrome 47 Extra Y

Triple X Syndrome 47 XXX

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Section II – Experimental Protocols

Experiment 1 – Onion Root Tip

Experimental Procedure

1. Set up the microscope and obtain an Allium cepa (onion root tip) slide.

2. Observe the rounded ends of the root tips for cells undergoing mitosis.

3. Find and sketch a cell in each stage of mitosis.

4. In each drawing label the cell wall and chromosomes.

5. If present, label the nuclear membrane, spindle fibers and cell plate.

Experiment 2 – Fish Blastula

Experimental Procedure

1. Set up the microscope and obtain a fish blastodisc slide.

2. Observe the fish egg cells undergoing division.

3. Find and sketch a cell in each stage of mitosis.

4. In each drawing label the cell membrane and chromosomes.

5. If present, label the nuclear membrane and spindle fibers.

Experiment 3 - Chromosome Labeling

Experimental Procedure

1. Use the karyotype given to label the circled chromosome image with the

correct lettered term. Each letter is only used once.

a. One pair of homologous chromosomes (tetrad)

b. Non-sister homologous chromosomes that can cross over genes

c. One chromatid (chromosome)

d. Sister chromatids (dyad)

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Experiment 4 – Meiosis

Experimental Procedure

1. Answer the following concept questions regarding the process of Meiosis.

2. Use the diagram to draw what happens when a cell with a diploid number

of two (2n = 2) goes through the process of meiosis.

a. Make sure to label chromosomes, sister chromosomes and tetrads

(every stage should have at least one label).

b. Make sure to denote the difference between the chromosomes from

the mother and father.

Experiment 5 – Karyotyping

Experimental Procedure

1. Obtain a container of chromosomes, magnetic board and chromosome key

for each student in your group.

2. Individually, using the key, place the chromosomes in the correct spaces

(based on size and shape) on the board.

3. Then answer the following questions.

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Section III – Lab Report Questions

Lab Report 11 Name:

Section/Date:

Experiment 1 – Onion Root Tip

Onion Root Tip - (Total magnification ________)

Prophase Metaphase

Anaphase Telophase

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Experiment 2 – Fish Blastula

Fish Blastula

(Total magnification ________)

Prophase Metaphase

Anaphase Telophase

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Experiment 3 – Chromosome Labeling

(Fill in the corresponding letter)

Experiment 4 – Meiosis

Questions

1. In what organ are gametes produced in the male body?

2. In what organ are gametes produced in the female body?

3. How many chromosomes does a normal somatic (body) human cell have?

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4. How many chromosomes does a normal human ovum have?

5. If a cell with eight chromosomes undergoes meiosis, it would produce

__________ cells with __________ chromosomes each.

6. If homologous chromosomes fail to separate in (Meiosis stage)

____________________, referred to as the process of ____________________,

the resulting cells will have either too many or not enough chromosomes.

7. Can any of the gametes produced when sister chromatids fail to separate

produce genetically accurate offspring? Explain why or why not.

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8. Draw in the missing chromosomes in the Meiotic process below.

Remember this organism has a diploid number of 2.

a. Diploid (2n) = ___________

b. Haploid (n) = ___________

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Experiment 5 – Karyotyping

Questions

1. Write the color and group of your karyotype kit.

2. How many chromosomes are present in your karyotype?

3. What is the gender of the individual? Female / Male

4. Which pair of chromosomes is abnormal?

5. Discuss what type of disorder the individual has and what

characteristics they possess (developmental, physical and mental).

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Section IV – Pre-Lab Questions

Pre-Lab for Lab 12 – Genetics

The following questions are designed to prepare you for the next lab exercise.

You need to read the next lab exercise in order to answer the following questions.

Questions

1. What is the difference between a Genotype and a Phenotype?

Use the Table on page 10 to answer the following questions.

2. List ALL possible genotypes for the tongue rolling trait.

3. List ALL possible phenotypes for the tongue rolling trait.

4. List ALL possible genotypes for the ear lobe trait.

5. List ALL possible phenotypes for the ear lobe trait.

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Use the Chart on page 4 to answer the following blood typing

questions.

6. What are ALL the possible genotypes for a person with the phenotype of B

blood?

7. Draw the Punnett Square for a cross between IAi and IBi.

Gametes → ↓

8. Draw the Punnett Square for a cross between IAiRr and IBiRr.

Gametes → ↓