Download Chromosome Theory of Inheritance

Chromosome Theory of Inheritance
Amy Pruitt – Blue Ridge High School
Dr. Nick Schlisler – Furman University
South Carolina Standards Addressed:
Standard B-4: The student will demonstrate an understanding of the molecular basis of heredity
and will predict inherited traits in organisms using Mendel’s principles: segregation, independent
assortment and dominance.
Indicators
B-4.2 Summarize the relationship among DNA, genes, and chromosomes.
B-4.5 Summarize the characteristics of the phases of meiosis I and II.
B-4.6 Predict inherited traits by using the principles of Mendelian genetics (including
segregation, independent assortment, and dominance).
B-4.7 Summarize the chromosome theory of inheritance and relate that theory to Gregor
Mendel’s principles of genetics.
B-4.8 Compare the consequences of mutations in body cells with those in gametes.
Standard B-1: The student will demonstrate an understanding of how scientific inquiry and
technological design, including mathematical analysis, can be used appropriately to pose
questions, seek answers, and develop solutions.
Indicators
B-1.1 Generate hypotheses based on credible, accurate, and relevant sources of
scientific information.
B-1.2 Use appropriate laboratory apparatuses, technology, and techniques safely and
accurately when conducting a scientific investigation.
B-1.5 Organize and interpret the data from a controlled scientific investigation by using
mathematics, graphs, models, and/or technology.
B-1.6 Evaluate the results of a controlled scientific investigation in terms of whether
they refute or verify the hypothesis.
B-1.9 Use appropriate safety procedures when conducting investigations.
Day 1-2: Mendelian Genetics
LEQ: How are Mendel’s principles of genetics used to predict characteristics that offspring
inherit from their parents?
Misconception Addressed: Dominant alleles are more desirable than recessive alleles.
Indicator: B-4.6: Predict inherited traits by using the principles of Mendelian genetics
(including segregation, independent assortment, and dominance). Taxonomy Level: 2.5-B
Understand Conceptual Knowledge
Previous knowledge: In 7th grade, students summarized how genetic information is passed from
parent to offspring by using the terms genes, chromosomes, inherited traits, genotype,
phenotype, dominant traits, and recessive traits (7-2.5) and used Punnett squares to predict
inherited monohybrid traits (7-2.6).
Vocabulary/Key Concepts: Gregor Mendel, genetics, heredity, law of segregation, law of
independent assortment, heritable factor, gene, allele, P generation, F1 generation, F2 generation,
Punnett square, monohybrid cross, dihybrid cross, homozygous dominant, homozygous
recessive, heterozygous, genotype, phenotype
Objectives: Students should be able to:
• Explain the significance of Mendel’s experiments to the study of genetics.
• Summarize the law of segregation and law of independent assortment.
• Predict the possible offspring from a cross using a Punnett square.
Teaching Strategies:
Activating Strategy - Opening Questions:
Provide various pictures of dogs. Students are to answer the following questions:
Do all dogs look alike? What types of features indicate a particular breed? Are
these features inherited? Can you tell individuals within a breed apart? What
does this tell you about the inheritance of these features?
Lesson Sequence:
Lecture/Discussion – Mendel’s experiment, alleles, Law of dominance, genotype
and phenotype
Activity using pre-made ribbon chromosomes to reinforce meiosis and introduce
the Law of Segregation and the Law Independent Assortment
Lead discussion to illustrate and outline how to set up a monohybrid cross.
Example can be purple (P) and white (p) flower color.
Illustrate a monohybrid crossing of the following zygotes: PP x pp; PP x Pp; Pp x
Pp
Lead discussion to illustrate and outline how to set up a dihybrid cross. Example
can be smooth, yellow (RRYY) and wrinkled, green (rryy) pea plants. Relate this
to Mendel’s experiments and illustrate the P, F1, and F2 generations of pea plants.
Wisconsin Fast Plants Lab – Analyze results. Materials and assistance provided
by Dr. Schlisler from Furman Univ.
Closure:
Practice: monohybrid and dihybrid crosses.
Practice: Calculating Genotypic and Phenotypic Ratios
Formative Assessment: Punnett square quiz
Day 3: Gene Linkage and Polyploidy
LEQ: How does the chromosome theory of inheritance relate to Mendel’s principles of
genetics?
Misconception Addressed: Crossing over occurs more frequently among genes that are closer
together.
Indicator: B-4.7: Summarize the chromosome theory of inheritance and relate that theory to
Gregor Mendel’s principles of genetics. Taxonomy Level: 2.4-B Understand Conceptual
Knowledge
Previous knowledge: This concept has not been addressed in earlier grades.
Vocabulary/Key Concepts: Chromosome theory of inheritance; Gene linkage; Crossing-over;
Recombination; Polyploidy
Objectives: Students should be able to:
• Summarize how the process of meiosis produces genetic recombination.
• Explain how gene linkage can be used to create chromosome maps.
• Analyze why polyploidy is important to the field of agriculture.
Teaching Strategies:
Activating Strategy:
Groups of three read paragraph in book and then discuss why genetic
recombination is important. Students will then discuss their points as a class
before we begin the lesson.
Lesson Sequence:
Lecture/Discussion – Genetic recombination, gene linkage and chromosome
mapping
Lecture/Discussion – Polyploidy
Closure:
Mini Lab – Map Chromosomes
Formative Assessment: Provide students with a problem and have them prepare a
chromosome map.
Day 4-5: Basic Patterns of Human Inheritance
LEQ: How are pedigress used to trace the inheritance of traits over several generations?
Misconception Addressed: Parents with normal phenotypes usually don’t have children with
genetic disorders.
Indicator: B-4.6: Predict inherited traits by using the principles of Mendelian genetics
(including segregation, independent assortment, and dominance). Taxonomy Level: 2.5-B
Understand Conceptual Knowledge
Previous knowledge: In 7th grade, students summarized how genetic information is passed from
parent to offspring by using the terms genes, chromosomes, inherited traits, genotype,
phenotype, dominant traits, and recessive traits (7-2.5) and used Punnett squares to predict
inherited monohybrid traits (7-2.6).
Vocabulary/Key Concepts: Carrier; Pedigree
Objectives: Students should be able to:
• Analyze genetic patterns to determine dominant or recessive inheritance patterns.
• Summarize examples of dominant and recessive disorders.
• Construct human pedigrees from genetic information.
Teaching Strategies:
Activating Strategy:
Brainstorming session: What genetic disorders do you already know about?
What are the characteristics/symptoms of those disorders? How do people get
genetic disorders?
Lesson Sequence:
Lecture/Discussion – Genetic disorders
o Single allele dominant: Huntington’s disease, polydactyly
o Single allele recessive: albinism, cystic fibrosis
Introduce Pedigrees
Activity/Lab – Analyzing Human Pedigrees - Materials provided by Dr. Schlisler
from Furman Univ.
Closure:
Exit Slip – 3-2-1 Summary Method
Day 6-8: Complex Patterns of Inheritance
LEQ: Since we have the same parents, why don’t I look like all of my siblings?
Misconception Addressed: If a person looks more like one parent than the other, they must
have inherited more genes from that parent.
Indicator: B-4.6: Predict inherited traits by using the principles of Mendelian genetics
(including segregation, independent assortment, and dominance). Taxonomy Level: 2.5-B
Understand Conceptual Knowledge
Previous knowledge: In 7th grade, students summarized how genetic information is passed from
parent to offspring by using the terms genes, chromosomes, inherited traits, genotype,
phenotype, dominant traits, and recessive traits (7-2.5) and used Punnett squares to predict
inherited monohybrid traits (7-2.6).
Vocabulary/Key Concepts: Incomplete dominance; Codominance; Multiple alleles; Epistasis,
Sex chromosome; Autosome; Sex-linked trait; Polygenic trait
Objectives: Students should be able to:
• Distinguish between various complex inheritance patterns.
• Analyze sex-linked and sex-limited inheritance patterns.
• Explain how the environment can influence the phenotype of an organism.
Teaching Strategies:
Activating Strategy:
Activity recording eye color characteristics of others in the class.
Lesson Sequence:
Illustrate a monohybrid cross for incomplete dominance. Example can be red
(RR), white (rr), and pink (Rr) flower color. Emphasize that the heterozygote
expresses the incomplete phenotype.
Illustrate a monohybrid cross for codominance. Example can be red (RR), white
(R’R’) and roan (RR’) hair coloring for horses. Emphasize that the heterozygote
expresses the incomplete phenotype.
Multiple Alleles: Blood types: A (IAi, IAIA); B (IBi, IBIB); AB (IAIB); O (ii)—use
various combinations to predict results
Heredity Lab/Activity: Human Facial Characteristics
Epistasis; Sex Determination; Dosage Compensation
Sex-Linked Traits: Illustrate genotypic and phenotypic ratios of offspring from
crossing parents with combinations of genotypes for genetic disorders such as:
o Hemophilia: XXh x XY …; XhXh x XY …; XXh x XhY …
o Colorblindness: XXc x XY …; XcXc x XY …; XXc x XcY …
Polygenic traits: skin, hair, & eye color; height
Data Analysis Lab – Interpreting the Graph – Relationship between sickle cell
anemia and other complications.
Closure - Formative Assessment:
Punnett square problems with complex patterns of heredity.
Day 9-10: Chromosomes and Human Heredity
LEQ: How are organisms affected by mutations in body cells versus mutations in sex cells?
Misconception Addressed: If a rare disorder appeared only once in a couple’s family, there is
no need for the couple to have their developing baby tested for the disorder.
Indicator: B-4.7: Summarize the chromosome theory of inheritance and relate that theory to
Gregor Mendel’s principles of genetics.
Indicator: B-4.8: Compare the consequences of mutations in body cells with those in gametes.
Previous knowledge: This concept has not been addressed in earlier grades.
Vocabulary/Key Concepts: Karyotype; telomere; nondisjunction; chromosomes, genes, cell
differentiation, cell growth, cancer, tumor, benign tumor, malignant tumor, carcinogen, mutagen,
metastasis, carcinoma, sarcoma, lymphoma, leukemia, growth factors, sex cells (gametes),
somatic (body) cells
Objectives: Students should be able to:
• Distinguish normal karyotypes from those with abnormal numbers of chromosomes.
• Define and describe the role of telomeres.
• Relate the effect of nondisjunction to Down Syndrome and other abnormal chromosome
numbers.
• Assess the benefits and risks of diagnostic fetal testing.
Teaching Strategies:
Activating Strategy:
Students are given various karyotypes to see if they can determine what, if
anything, is wrong with it.
Lesson Sequence:
Karyotype studies
Nondisjunction: Down syndrome (trisomy-21)
Fetal Testing – Amniocentesis, Chorionic Villi Sampling, Fetal Blood Sampling
Construct concept maps to illustrate mutations of gametic and somatic cells.
Closure and Formative Assessment:
Karyotype Lab – Materials and assistance provided by Dr. Schlisler from Furman
Univ.
Day 11: Culminating Activity: Nov. 21, 2008 - Field Trip - Genetic Roots Lab at Furman
University http://www.biol.sc.edu/~elygen/SCiLab%20Main.htm
Genetic Roots
A SCienceLab activity
Dr. Bert Ely
Department of Biological Sciences
University of South Carolina
715 Sumter St.
Columbia, SC 29208
[email protected]
Additional Contributors: Brice Gill, Teresa Pizzuti, Karen Walton, and
Jonathon Singer
DNA, a Link to Your Ancestors
Did you know that shortly after George Washington became president, a young woman gave
birth to a baby girl and that you have DNA that is identical to some of that baby’s DNA? A few
years later, a boy was born in a distant place and his mother worried about whether he would
survive. Fortunately, he did because part of the DNA sequence from one of his children is now in
your cells. Copies of those DNA segments have passed from parent to child from generation to
generation until one of your parents passed them to you! In fact, if that baby was your great,
great, great grandmother’s great, great, great grandmother, then she was one approximately 1000
people who were born at that time and contributed to your DNA!
DNA is the basis of life. It contains a set of instructions for building all of the proteins and RNA
found in a cell. Those instructions are written in a code called the genetic code. The code
consists of 4 bases, Adenine, Cytosine, Guanine, and Thymine, often referred to as A, C, G, and
T. The 4 bases are read in groups of three so there are 64 possible combinations (4 possibilities at
each of 3 positions). Each combination of three bases forms a code word called a codon. All but
three of these codons code for one of the 20 amino acids commonly found in proteins. The order
of these codons on the DNA determines the order of the amino acids in the protein that is made
from this DNA code. The remaining codons are called stop codons because they tell the cell to
stop making a particular protein. A gene contains a set of code words followed by a stop codon.
The set of code words show the cell how to make a particular protein. Thus, a gene is a set of
instructions for a making a particular protein.
Your DNA is packaged in chromosomes. Each chromosome contains lots of genes so it codes for
lots of proteins. You got one set of chromosomes from your mother and a second set from your
father. Since, you have two copies of each of your genes, if one copy of a gene happens to
contain a mistake in the genetic code, you can use the other copy to make the corresponding
protein.
In this exercise, students will isolate their own DNA and amplify a portion of it so that they can
see some of the genetic diversity that is present in their class.
UNIT OF STUDY: GENETIC ROOTS
CLASS DESCRIPTION: HIGH SCHOOL
Science Standards addressed:
B-1.1 Generate hypotheses based on credible, accurate, and relevant sources of scientific
information.
B-1.2 Use appropriate laboratory apparatuses, technology, and techniques safely and accurately
when conducting a scientific investigation.
B-1.6 Evaluate the results of a controlled scientific investigation in terms of whether they refute
or verify the hypothesis.
B-1.9 Use appropriate safety procedures when conducting investigations.
B-4.2 Summarize the relationship among DNA, genes, and chromosomes.
B-4.6 Predict inherited traits by using the principles of Mendelian genetics (including
segregation, independent assortment, and dominance).
B-4.7 Summarize the chromosome theory of inheritance and relate that theory to Gregor
Mendel’s principles of genetics.
B-4.8 Compare the consequences of mutation in body cells with those in gametes.
Objectives:
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Be able to identify the chemical building blocks of DNA.
Understand the principles of gel electrophoresis and be able to isolate DNA.
Understand how DNA codes for traits.
Use DNA analysis techniques to detect genetic diversity.
Laboratory Procedures
Student DNA Sample Isolation
DNA can be obtained from any tissue. To keep the procedure simple, safe and non-invasive, we
will use cheek cells. The student simply swabs the inside of his cheek and puts the swab back in
the protective tube! No pain. No risk. After the DNA isolation is completed, a portion of the
students mitochondrial DNA will be amplified using the PCR technique.
MATERIALS
Sterile buccal swabs (pronounced “buckle”)
DNA isolation tubes
QuickExtract Solution
Microfuge
Water baths at 65 C and 98 C
Tubes containing PCR reagents
PROCEDURE
1. Label a microcentrifuge tubes (1.5ml capacity) and add 500µl of QuickExtract DNA
Extraction Solution.
Note: Be sure to use boil-proof microcentrifuge tubes!
2. Rinse out your mouth with water if it contains food particles.
3. Collect tissue by rolling the sample collection swab firmly on the inside of the cheek,
approximately 20 times on each side, making sure to move the brush over the entire
cheek.
4. Place the swab end of the collection swab into the microcentrifuge tube containing
extraction solution and rotate the swab a minimum of 5 times. While removing the swab
from the liquid, make sure to press it against the side of the tube several times to ensure
that most of the liquid remains in the tube.
5. Put the cap on the microcentrifuge tube and vortex the mix for 10 seconds. Incubate the
tube at 65ºC for 1 minute.
6. Remove the tube from incubation and vortex for 15 seconds.
7. Transfer the tube to 98ºC and incubate for 2 minutes.
8. Remove and vortex for 15 seconds.
9. Pipette 1 ul of your DNA into the PCR tube that matches your sample number.
10. Place your PCR tube in the PCR machine.
Agarose Gel Electrophoresis of Food Coloring Dyes
Agarose gel electrophoresis allows you to separate molecules according to size. It is one of the
most important procedures used in studies of DNA. To learn how to do it, we will use agarose
gel electrophoresis to show that food color dyes are often made up of more than one dye.
Before we start, let's think about what we are going to do. First of all what is agarose? It is a
polymer! Poly means many as in polygon (many sides). A polymer is made of many parts.
Agarose, a purified form of agar, is a polymer that is made entirely of sugar molecules. It is
produced by a kind of seaweed and is used to give thicker consistency to foods such as ice
cream. We use agarose because a solution of agarose and water forms a gel when it cools to
room temperature. It is sort of like jello except that it does not get soft when it gets warm.
Molecules like food dyes can move through an agarose gel, but the larger they are, the slower
they move. To understand the process, think about a backyard or a forest that is full of trees. If
you watch, you can see that small birds fly through the branches of the trees almost as if they
were not there. What about a large bird like a hawk or an owl? They can only fly through larger
spaces among the branches or they have to fly around the trees. Therefore, they cannot fly as fast
as the smaller birds. In the same way, small molecules can move quickly among the agarose
branches in the gel, but larger molecules move more slowly because they have to pass through
larger spaces.
What is electrophoresis? Electrophoresis is process that uses electricity to pull molecules from
one place to another. Remember our example above about large vs small birds? How do you
think that example relates to gel electrophoresis? If you look at the gel box, you will see that it
has two bare wires called electrodes. One is connected to a red wire and has a positive charge,
and the other is connected to a black wire and has a negative charge. Most dyes have a negative
charge so they are attracted by the positive charge and move through the gel towards the positive
electrode. Therefore, we are going to use agarose gel electrophoresis to pull dye molecules
through an agarose gel and separate them according to size.
Materials
Food color dyes
Agarose
SBA Buffer
Gel apparatus
Power supply
Pipettes
Balance
Heat source
Liquid measure
Procedure
1) Weigh out 1.2 grams of agarose and add it to 100 ml of room temperature SBA buffer. Swirl
to make sure that there are no clumps. Boil the mixture to melt the agarose by heating it in a
microwave. As soon as it comes to a boil, open the microwave and swirl the flask without
removing it from the microwave. Be sure to handle the hot flask with a glove or hot pad! After
swirling, remove the flask and look at the contents. You will see clear particles moving in the
solution. These particles are unmelted agarose. Return the flask to the microwave and repeat the
boiling and swirling process until you can no longer see the agarose particles. Repeat the boiling
and swirling process one more time to be sure all the agarose particles are in solution.
2) Let the agarose solution cool but not too much. It should feel very hot but not so hot that you
cannot hold the flask. Pour enough into the gel tray to make a gel that has thickness of about 3
mm. Insert your gel comb into the liquid agarose in the gel tray. Cover the rest of the agarose, let
it cool, and save it for your next experiment. (To reuse a solidified agarose solution, simply
reheat it with occasional swirling until the solution is uniformly liquid).
3) Once the agarose in your gel tray has solidified, remove the comb. The holes left by the teeth
of the comb are called wells. Place the gel tray in the gel box. Add enough SBA buffer to the gel
box to cover the gel with about 2 mm of buffer.
4) Slowly and carefully transfer 3 microliters of one of the food dyes into one of the wells.
Repeat with the other dyes. (Use every other well of the gel.)
5) Place the lid on the gel box, and turn on the power supply to 200 volts.
6) Look at the gel from time to time to see how the dyes are separating from one another. Notice
how each dye moves in a straight line from its well towards the positive electrode. Thus, just like
swimmers at a swim meet, each dye stays in its own lane. Also, you can see some dyes moving
faster than others. Once the fastest dye moves about two thirds of the way through the gel, turn
off the power supply and remove the gel tray from the gel box.
7) For each of the food color dyes, write down the colors you expect to see in the row labeled
hypothesis. After electrophoresis, observe which colors are present in each dye, the relative
amounts of each color, and the relative distance traveled by each color.
Blue
Hypothesis
Observed
Red
Dye
Green
Yellow
DNA Electrophoresis of amplified DNA
Agarose gel electrophoresis can be used to separate DNA molecules according to size. The
procedure is the same as when we separated the food dyes. In fact, we load a dye with our DNA
samples so that we can monitor the progress of the electrophoresis. The dye solution also
contains glycerol to provide a dense mixture that will stay in the bottom of the well.
MATERIALS
DNA samples
DNA size standard
Loading dye solution
Agarose
SBA buffer
Ethidium Bromide solution
UV light box
Gel box and tray
Power supply
PROCEDURE
1. Pour an agarose gel and cover it with SBA buffer as described previously.
2. Spot 1 ul of the loading dye onto a piece of parafilm.
3. Pipette 5 ul of your DNA sample onto the spot, mix by pipetting up and down and then load
the mixture into a well of the agarose gel.
4. Pipette 5 ul of a solution containing a DNA size standard into an empty well of the gel.
5. Place the lid on the gel box and turn on the power supply to 200 volts.
6. After the tracking dye has migrated half the way through the gel, turn off the power, remove
the gel from the gel box.
7. Observe the DNA by placing the gel on a UV light box. What kind of variation do you see?
DNA EXTRACTION FROM ONION
Prepared by the Office of Biotechnology, Iowa State University
INTRODUCTION
DNA is present in the cells of all living organisms. This procedure is designed to extract DNA
from onion in sufficient quantity to be seen and spooled. It is based on the use of household
equipment and supplies.
MATERIALS
For teacher preparation
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two 4-cup measuring cups (1000 ml) with ml markings
one 1-cup measuring cup (250 ml) with ml markings
measuring spoons
sharp knife for cutting onion
large spoon for mixing
food processor or blender
thermometer that will measure 60o C (140o F), such as a candy thermometer
strainer or funnel that will fit in a 4-cup measuring cup
cheese cloth (or a coffee filter – takes longer)
hot tap water bath (60o C)(a 3-quart saucepan works well to hold the water)
ice water bath (a large mixing bowl works well)
distilled water
light-colored dishwashing liquid or shampoo, such as Dawn or Suave Daily Clarifying
Shampoo
large onion
table salt, either iodized or non-iodized
Supplies provided to the class
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1 test tube for each student that contains the onion solution.
Pasteur pipettes or medicine droppers
95% ethanol (grain alcohol)
laboratory instructions
TEACHER PREPARATION
1. Set up hot water bath at 55-60o C and an ice water bath.
2. For each onion, add one level 1/4 teaspoon (1.5 g) of table salt to 90 ml of distilled water
in a 1-cup measuring cup (250 ml beaker). After the salt is dissolved, add one tablespoon
(10 ml) of liquid dishwashing detergent or shampoo and mix gently to avoid foaming.
3. Coarsely chop one large onion with a food processor or blender (may be done by hand if
neither is available) and put into a 4-cup measuring cup (1000 ml). For best results, do
not chop the onion too finely. The size of the pieces should be like those used in making
spaghetti. It is better to have the pieces too large than too small.
4. Cover chopped onion with the 100 ml of solution from step 2. The liquid detergent causes
the cell membrane to break down and dissolves the lipids and proteins of the cell by
disrupting the bonds that hold the cell membrane together. The detergent causes lipids
and proteins to precipitate out of the solution. NaCl enables nucleic acids to precipitate
out of an alcohol solution because it shields the negative phosphate end of DNA, causing
the DNA strands to come closer together and coalesce.
5. Put the measuring cup in a hot water bath at 55-60o C for 10-12 minutes. During this
time, press the chopped onion mixture against the side of the measuring cup with the
back of the spoon. (Do not keep the mixture in the hot water bath for more than 15
minutes because the DNA will begin to break down.) The heat treatment softens the
phospholipids in the cell membrane and denatures the DNAse enzymes which, if present,
would cut the DNA into small fragments so that it could not be extracted.
6. Cool the mixture in an ice water bath for 5 minutes. During this time, press the chopped
onion mixture against the side of the measuring cup with the back of the spoon. This step
slows the breakdown of DNA.
7. Filter the mixture through four layers of cheese cloth placed in a strainer over a 4-cup
measuring cup. When you filter the onion mixture, try to keep the foam from getting into
the filtrate. It sometimes filters slowly, so you might want to put the whole set up in the
refrigerator and let it filter overnight.
8. Dispense the onion solution into test tubes, one for each student. The test tube should
contain about 1 teaspoon of solution or be about 1/3 full. For most uniform results among
test tubes, stir the solution frequently when dispensing it into the tubes. There is not an
advantage to dispensing more than one teaspoon of solution into a test tube. The solution
can be stored in a refrigerator for about a day before it is used for the laboratory exercise.
When the solution is removed from the refrigerator, it should be gently mixed before the
test tubes are filled.
DNA EXTRACTION FROM ONION
STUDENT INSTRUCTIONS
The process of extracting DNA from a cell is the first step for many laboratory procedures in
biotechnology. The scientist must be able to separate DNA from the unwanted substances of the
cell gently enough so that the DNA is not broken up.
We have already prepared a solution for you, made of onion treated with salt, distilled water and
dishwashing detergent or shampoo. An onion is used because it has a low starch content, which
allows the DNA to be seen clearly. The salt shields the negative phosphate ends of DNA, which
allows the ends to come closer so the DNA can precipitate out of a cold alcohol solution. The
detergent causes the cell membrane to break down by dissolving the lipids and proteins of the
cell and disrupting the bonds that hold the cell membrane together. The detergent then forms
complexes with these lipids and proteins, causing them to precipitate out of solution.
PROCEDURE
1. Add cold alcohol to the test tube to create an alcohol layer on top of about 1 cm. For best
results, the alcohol should be as cold as possible. Slowly pour the alcohol down the inside
of the test tube with a Pasteur pipette or medicine dropper. DNA is not soluble in alcohol.
When alcohol is added to the mixture, all the components of the mixture, except for
DNA, stay in solution while the DNA precipitates out into the alcohol layer.
2. Let the solution sit for 2-3 minutes without disturbing it. It is important not to shake the
test tube. You can watch the white DNA precipitate out into the alcohol layer. When
good results are obtained, there will be enough DNA to spool on to a Pasteur pipette.
DNA has the appearance of white mucus.
DNA Inheritance Game
State Standard – sex cells result in a new combination of genetic information different from
either parent.
This game is whimsical and a lot of fun. At the same time, it teaches the concept that physical
traits are encoded by genes that are found on chromosomes.
Contents:
1 bag per student, containing 10 snap beads (red, blue, green, orange; if other colors are used
change the chart below). Alternatively, regular beads can be threaded onto a straightened paper
clip.
Goal: Identify 6 bases on a DNA strand (2 amino acids) and use the “secret decoder” to uncover
the participant’s eye color and hair color.
Play:
1) Hand out one bag to each student.
2) Instruct them to make a row of six beads to represent a chromosome.
3) Explain that it takes 3 bases to code for an amino acid—the building blocks of
proteins. Each gene codes for a string of amino acids that make a protein. However, sometimes a
change in just one of those amino acids can change a trait. For simplicity, all of our traits are
going to be determined by a single amino acid. In this case, we are building proteins for eye
color and hair color (Or you can choose whatever characteristic or feature you’d like). The first
3 code for eye color and the second 3 for hair color.
Once they have built their DNA strand, you help them “decode” it. It is the 1st of the 3
that determines the characteristic as shown:
Red first:
Blue first:
Green first
Orange first
Eye Color
brown
blue
green
grey
Hair Color
red
black
blonde
orange
Second round
Remove the beads and repeat the process to generate genes for height and skin covering.
Red first:
Blue first:
Green first
Orange first
Height
tall
short
medium
8 feet
Skin covering
feathers
scales
fur
slime
Third Round
Remove the beads and repeat the process to generate genes for numbers of toes and limbs.
Red first:
Blue first:
Green first
Orange first
# toes
2
1
5
6
# limbs
2 legs and 2 wings
4 legs
6 legs
8 legs
Ask the students to identify an animal that has each of the characteristics.
Fourth round
Remove the beads and repeat the process to generate genes for height and skin color.
Red first:
Blue first:
Green first
Orange first
Tail
long
short
no tail
curled
Skin color
red
yellow
green
purple