home lab manual unit 1

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Online BIO 100A: Survey of Bioscience Laboratory

Laboratory Manual

Part I

(Version 4.0)

National University

Written by:

Michael R. Maxwell

&

Omar Clay

2005; 2007; 2009; 2011


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Table of Contents

Part 1:

Lab 1: The Metric System, Measurement, and Uncertainty 6

Lab 2: Enzymes and pH. 9

Lab 3: Cellular Respiration 12

Lab 4: Genetics: From DNA to Heredity 19


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Foreward

This laboratory manual is written specifically for students taking the online course BIO 100A.Materials and activities are designed to be performed at home with minimal cost and hazard tostudents. This manual's content is partially based on the assigned manual for onsite BIO 100A.

Bio 100A is intended to be taken by students that have already completed Bio100. Studentsshould also have the textbook for BIO100, as concepts in 100A will be referred to this textbook.

Juliann Downing of National University provided assistance in the writing of this manual.


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BIO 100A: Materials List

Students need to obtain the following materials for successful completion of this course.Emphasis has been placed on low cost, easily found items. Total estimated cost is less than $50.

Item Availability Approx. costActive dry yeast (or rapid rise) Grocery $3.99Six small bottles- .5L plastic water bottles Household or Grocery $3.00Candy (or meat) Thermometer (must display temperatures between 100 -130 F)

Household or Grocery $5.99Six balloons (5 or greater diameter) Grocery $1.99Safety goggles (optional but recommended) Hardware $2.50Hydrogen peroxide (1 pint, 473 ml) Grocery (First Aid) $ 1.00Household ammonia Grocery (Cleansers) $ 1.65White vinegar Household or Grocery $ 1.29Rubbing alcohol (75% or greater) Household or Grocery $ 1.49

One large mushroom (common or shiitake; lab 7) Household or Grocery $ 0.20One whole potato (lab 2) Household or Grocery $ 0.70Celery stalk (labs 5 & 6) Household or Grocery $ 1.00Red and Blue food coloring (any two colors is fine) Household or Grocery $3.00Pea pod (sugar snap or snow pea; lab 5) Grocery $ 0.10Dry lima beans (3) Grocery $ 0.50Radish seeds (1 pack) Grocery $1.99Ziplock bags (4) Household or Grocery $ 3.99Two of the following animals (lab 7):

Garden snail NeighborhoodSquid Grocery $ 4.00

Earthworm or night crawler (large) ` Neighborhood or Bait store $ 2.70One crustacean Grocery variesHouse cricket (adult) Pet store $ 0.10Ladybug NeighborhoodMackerel Bait store $ 3.00

Ruler (with metric) Household or GroceryIndelible marker Household or GrocerySucrose (white sugar) Household or GroceryString Household or GroceryWatch/ Clock (with seconds display) HouseholdMeasuring cup Household or Grocery $ 2.00

Measuring spoons Household or Grocery $ 3.00Kitchen pot HouseholdLiquid dish soap Household or GroceryLarge pine cone with open scales Neighborhood or ParkFascicle (bundle) of pine needles Neighborhood or ParkTable Salt Household or GroceryPaper towels Household or GroceryDisposable plates Household or Grocery


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Lab 1: The Metric System, Measurement, and Uncertainty

Materials neededRuler (with metric)String

Introduction

Accurate measurement of the natural and physical world is fundamental to science. Modernscientists use the metric systemin their measurements. The metric system was developed inFrance in the late 1700s, and is now commonly used in most countries. A main advantage of themetric system is that it is based on multiples of 10. This is much easier than the English systemof 12 inches to the foot, 16 ounces to the pound, and 16 cups to the gallon.

Americans are often unfamiliar with some of the basic units of the metric system; thus, it canpresent a difficulty. In this laboratory, you will develop an understanding of the metric system

and use it to measure common objects. You will also learn about how to report uncertainty inyour measurements. Estimating measurement uncertaintyis a critical component of scientificreporting that you will use in later labs.

Metric units

The basic measurements of the metric system are:1. Length, expressed in meters(m).2. Mass (weight), expressed in grams(g).3. Volume (capacity), expressed in liters(l).

These units have the following English equivalents. One meter is roughly 3 feet (1 yard), orslightly longer than one pace. One gram is very light; one paperclip is about 1 gram, while anickel is about 5 grams. Standard weights are often expressed in kilograms (1,000 grams). Onekilogram is roughly 2 pounds. One liter is roughly 1 quart, so there are about 4 liters in 1 gallon.

For each of these units, large or small amounts are expressed by prefixes that reflect multiples of10, as the following table shows.

Prefix Symbol Power of 10 Length Mass Volumegiga- G 109= 1,000,000,000mega- M 106= 1,000,000

kilo- k 10

3

= 1,000 kilometer (km) kilogram (kg) kiloliter (kl)hecto- h 102= 100deka- da 101= 10

100= 1 meter (m) gram (g) liter (l)

deci- d 10-1= 0.1centi- c 10-2= 0.01 centimeter (cm) centigram (cg) centiliter (cl)milli- m 10-3= 0.001 millimeter (mm) milligram (mg) milliliter (ml)

micro- 10-6= 0.000001 micrometer (m) microgram (g) microliter (l)


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Using these prefixes, the following exact conversions can be made:1 meter = 100 cm = 1,000 mm = 3.28 feet = 39.37 inches1 inch = 2.54 cm [1 cm is slightly less than a half-inch]1 mile = 1.61 km = 5,280 feet1 kilometer = 1,000 m = 0.621 miles [1 km is somewhat longer than a half-mile]

1 kilogram = 1,000 kg = 2.2 pounds1 liter = 1,000 ml = 1.06 quarts = 0.264 gallons

Temperature

The metric unit of temperature is degrees centigrade( C). The Celsiustemperature scale wasdeveloped by the Swedish astronomer Anders Celsius in 1742. Nearly every country in theworld uses the Celsius system. It can be confusing for traveling Americans when the morningnews announces a "nice day" of 24 degrees. This sounds cold, but 24 C is actually 75 F.Temperature relates to the average energy of movement (kinetic energy) of molecules in theenvironment.

The Celsius system is based on the freezing and boiling points of water:Celsius (C) Fahrenheit (F)

Water boils 100 212Water freezes 0 32Absolute zero1 -273 -395

Exact conversions between the two scales are:

C =9

5 (F - 32)

F = (59 C) + 32

Uncertainty Estimation

A key aspect of accurate measurement and reporting of measurement is estimating the precisionof your measurements. For instance, when someone reports that it took twenty minutes to cook aparticular item, do they mean it took twenty minutes plus or minus a minute? Or do they meantwenty minutes plus or minus five minutes? This kind of information is very important if you aretrying to exactly replicate previous experiments.

Thus, in addition to reporting a measurement, scientists try to estimate the range of values thatthey are certain captures the object being measured. In this measurement lab, you will estimatethe uncertaintyin your measurements. A good way to do this is to make and record themeasurement and then come back and make the measurement again. If this is done several times,you will get a good idea of how precisely you can measure the given object. No scientific

1Absolute zero is the temperature at which all molecular motion stops.


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measurement is exact, as every measurement technique has limits. In scientific parlance, theuncertainty in a measurement X is often referred to as X (called "delta X").


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Lab 2: Enzymes and pH

Materials neededOne whole potatoHydrogen peroxide (1 pint, 473 ml)

Household ammoniaWhite vinegar4 disposable clear glassesTap waterSharp knifeRuler (metric)Marker

Figure 2.1. Catalase.Introduction

An enzymeis a molecule that increases the rate of chemical reactions. Enzymes are extremelyimportant for all organisms and have been described as the machinery of the cell. They areinvolved in all of a cells essential activities, metabolic processes, protein and DNA synthesis,etc. Enzymes tend to be very large molecules, and their function is tied to their complexmolecular structure (see Figure 2.1). Enzymatic functionality tends to be sensitive toenvironmental conditions. Temperature and pH, for example, both affect the activity of anenzyme.

The pH of a solution is a measurement of its acidity. A low value of pH corresponds to thesolution being acidic. In solution, acids tend to form H

+ions that will react with many othermolecules. A high pH value means a highly alkaline(basic) solution. In solution, bases tend to

from OH

-

ions that will react with many molecules. Both highly acidic and highly alkalinesolutions are corrosive. They can also counteract one another and form water. Pure water, whichis neutral(neither acidic or alkaline) has a pH = 7. The pH values of some common substancesare as follows:


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pH ExamplesVery acidic 0

1 Battery acid2 Lemon juice; gastric juice (in stomach)

3 Vinegar; Grapefruit juice4 Tomato juice5 Coffee6 Urine; saliva; milk (pH = 6.5)

Neutral 7 Distilled water; human blood; semen (pH = 7.4)8 Egg white; seawater (pH = 8.4)9

10 Milk of magnesia (pH = 10.5)11 Household ammonia (pH = 11.7)12 Household bleach13 Oven cleaner (pH = 13.5)

Very alkaline 14

Each enzyme has a pH at which the rate of the reaction it catalyzes is optimal. In thefollowing experiment, you will investigate the optimal pH for Catalase. Catalaseis acommon enzyme, present in most cells. It speeds the breakdown of hydrogen peroxide(H2O2), a toxic byproduct of many cellular reactions, into water (H2O) and oxygen gas(O2). A single molecule of Catalase can convert hundreds of thousands of molecules ofhydrogen peroxide to water and oxygen per second. A potato will serve as the source ofCatalase. As the reaction occurs, bubbling will become visible as oxygen is produced.

2 H2O2 --------------------> 2 H2O + O2Catalase

The chemical equation above indicates that the reactants(H2O2) on the left hand side aretransformed into the products(H2O and O2) on the right hand side. Catalase being below thearrow indicates that this enzyme catalyzes this reaction. For an enzyme or a molecule to beconsidered a catalyst for a reaction, it must increase the likelihood of the reaction taking placeand must not itself be used up in the reaction. Catalase is the name of this particular enzyme andit is a catalystfor this particular reaction.

This laboratory is based on the lab manual by Mader. Information on enzymes can be found inthe BIO 100 textbook and in the online Supplemental and AV library.

Activity

1. CAUTION: AMMONIA IS CORROSIVE. Prolonged exposure to vapors may causebreathing difficulties. Open a window when conducting this experiment. Contact with skinmay cause irritation. If contact occurs, wash immediately with lots of water.

2. Peel the skin off of the potato with the knife. Chop the potato into small chunks.


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3. Label each cup:#1: Water + H2O2#2: Potato + Water + H2O2#3: Potato + Vinegar + H2O2

#4: Potato + Ammonia + H2O2

4. Mark each cup with a dash at the 1-inch, 2-inch, and 3-inch heights (i.e., 2.5-cm, 5.0-cm, 7.5-cm).

5. Fill cup #2, #3, and #4 with approximately 1 inch (2.5 cm) of potato. Make sure thatthe amount of potato in each cup is approximately the same.

6. Fill the cups as follows:#1: tap water to the 2-inch (5.0-cm) mark.#2: tap water to the 2-inch (5.0-cm) mark.

#3: vinegar to the 2-inch (5.0-cm) mark.#4: ammonia to the 2-inch (5.0-cm) mark.

7. Gently stir up the cups that contain potato or let the cups sit for 5 minutes to allow thepotato to soak up the liquid.

8. Fill all cups to the 3-inch (7.5-cm) mark with hydrogen peroxide, H2O2. The layeringof the cups should now be as follows:

Cup 1 Cup 2Hydrogen peroxide Hydrogen peroxideWater WaterNo Potato Potato

Cup 3 Cup 4Hydrogen peroxide Hydrogen peroxideVinegar AmmoniaPotato Potato

9. Observe bubbling for 2-3 minutes and complete Table 2.1 of the Lab Report.

10. Without any Catalase enzymes present, cup #1 should show minimal activity. Explorethe use of another material to see if Catalase is present in cup #1. Other material canbe chopped spinach, lettuce, meat, apple, or egg. Use the same volume that you usedwith the potato so you can compare the relative rates of activity. Record yourobservations and conclusions in the rest of Lab Report 2.


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Lab 3: Cellular Respiration

Materials neededActive dry yeast (alternatively Rapid rise or instant yeast)Six small bottles- .5L plastic water bottles (alternatively test tubes)

Candy Thermometer (alternatively oven/meat thermometer)Note: must be capable of reading temperatures between 100 -130 F.

Six same sized balloons (5 diameter or bigger)Safety goggles (recommended)Indelible markerSucrose (sugar)StringRulerWatch/ ClockMeasuring CupMeasuring spoons

Kitchen pot

Optional MaterialsVinegarAmmoniapH paperBeef bouillonFructose or honeySugar substitute(e.g. NutraSweet)

Figure 3.1. Lab materials.Introduction

In this experiment, you will investigate cellular respiration. By monitoring the volume of CO2gas produced and the growth of a yeast medium (dependent variables), you will investigate therole of sugar, temperature, and another independent variable of your choosing in cellularrespiration. You will also learn about yeast, cellular respiration, experimental design andestimating measurement uncertainties.

Cellular Metabolism

Cellular respirationis a set of biochemical reactions essential to cellular metabolism. In thisprocess, sugars inside of cells are broken down into adenosine triphosphate (or ATP) whichserves as a source of cellular energy. Cellular respiration also produces carbon dioxide (CO2) andother products. The production of CO2is the chief way that CO2enters the atmosphere and isthus a primary aspect of the carbon cycle; the other primary leg of the carbon cycle is


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photosynthesiswhich captures CO2from the atmosphere and uses solar energy to producesugars.

The first step in cellular respiration occurs in the cell cytoplasm and is called glycolysis(Figure3.2). In glycolysis, a single glucose (sugar) molecule is broken down into two pyruvate

molecules and two ATP molecules.

1 C6H12O6 2 C3H3O3-+ 2 ATP

glucose pyruvate energy

There are two principle types of cellular respiration (Figure 3.2). First, in the presence ofoxygen, aerobic respirationcan take place in the cell's mitochondria, where pyruvate andoxygen are used to produce CO2and 36 ATP. The mechanisms by which this occurs are theKrebs cycle and the Electron transport chain.

2 C3H3O3- + 6 O26 CO2+ 6 H2O + up to 34 ATP

pyruvate oxygen carbon water energygas dioxide gas

Second, in the absence of oxygen, cells can engage in anaerobic respirationwhich takes placein the cytoplasm. One form of anaerobic respiration occurs in the muscle cells of animals whenthey are using more oxygen than the blood can supply. This is known as lactic acidfermentationbecause it produces lactic acid. Ultimately, lactate can be used to produce somemore ATP. Some fungi and bacteria also use this biochemical pathway. Yeast and some bacteriaengage in another form of anaerobic respiration known as ethanol fermentation. This processdoes not provide more ATP but does produce CO2, ethanol (drinking alcohol) and maintains thebiochemical conditions necessary for continuing glycolysis in the cytoplasm.

Figure 3.2. Cellular respiration. [Figure from Johnson and Raven, 2004, Biology, HoltRinehart and Winston, p. 110]


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Yeast

Yeastis a single-celled fungus. These cells are typically 3-4 microns in size, but dont let thatfool you into thinking that they are not important to humankind. A particularly import kind of

yeast is Saccharomyces cerevisiae. These organisms are used to ferment the sugars of grains(wheat, barley, rice, corn, etc.) and other foods (e.g., grapes) to produce alcoholic drinks(whiskey, beer, wine, etc.) and to make bread rise. Yeast is also used in the production of somecheeses, and is being used in the field of bioremediation and ethanol fuel production. Yeast-likefungi are also normal inhabitants in the mouth, vagina, skin, and intestines.

Figure 3.3.

Left.Saccharomycescerevisiaeas seenthrough a microscope.Right.Active dried

yeast is a granulatedform in which yeast iscommercially sold.

Experiment: Investigation of CO2production from cellular respiration in yeast

0. Read through the following instructions thoroughly before beginning your experiment.Exercise caution and be mindful of safetyas you work with hot water and plastic bottles.

1. Collect all of your materials in a clean safe place. Decide what alternate experimentalconditions you will examine. Ideas for alternate experimental conditions (e.g., sugarsubstitute, pH change, yeast conditioning, temperature) are described more fully below.

2. Make sure that your thermometer and five plastic bottles will all fit inside of your kitchen pot(Figure 3.1). Make sure that your balloons fit tightly on your bottle necks (Figures 3.4 and3.5). You may also want to tie your bottles together with string so that they will not float inthe bath water.

3. Make sure that each bottle is clean and dry. Add 2 teaspoons of yeast to each bottle with thepossible exception of #6, which will depend upon your alternative choice.


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Figure 3.4. Labeled, loaded, and ready to grow.

4. Fill each bottle with cup of water. Be sure that each receives the same kind and quantity ofwater. For instance, if you use tap water, use it with all of the bottles. Write down what kindof water you use. If you are going to run an experiment on pH and have pH paper, measurethe pH of the water.

5. Record the independent variables (i.e., the conditions under experimental control) for eachyeast population (bottle). The independent variables are Sugar, Yeast, and Water in Table3.1. Do not measure the height (in cm) of the yeast solution until Step 8.

Table 3.1. Variables in the experiment.

Bottle Sugar Yeast Water Yeast solutionheight (in cm)

To be heated in warm water bath?

1 1 teasp 2 teasp cup No. Leave this bottle at room temp.

2 1 teasp 2 teasp cup Yes.

3 1 teasp 2 teasp cup Yes. Replicates bottle #2.

4 1/3 teasp 2 teasp cup Yes.

5 No Sugar 2 teasp cup Yes.

6 cup

6. Notice that Bottles #2 and #3 have identical conditions. This will allow you to gauge theprecision of your experimental method. Bottle #6 is to be used in an experiment of yourchoosing. You should change only one of the independent variables and keep the othersconstant. For instance, you might choose to investigate whether yeast can grow as well withsomething other than sugar, such as beef bouillon, NutraSweet, saccharine or a higherquantity of sugar (e.g., 2 teaspoons). If you do this, be sure to keep the yeast quantity


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constant at 2 teaspoons and heat the bottle like the others. Other ideas include: altering thepH of the water by adding a measured amount of ammonia or vinegar; changing the amountof yeast in the bottle; microwaving the dry yeast before trying to grow them (microwavingmight kill the yeast), or seeing if the yeast can grow in the cold by placing Bottle #6 in therefridgerator instead of the warm water bath.

7. Replace the caps on each bottle and swirl the solutions thoroughly to insure that the yeast cellsare well distributed in the solution.

8. Remove the caps and replace them with balloons. Stretch the mouth of each balloon over themouth of each bottle (Figure 3.5). Make sure that the balloon/bottle connection is secure; ifnecessary, use tape or string. Measure the height of the yeast solutions in the bottles andrecord them in Table 3.1 (they should all be pretty much the same).

Figure 3.5. CO2production and yeast growth after ~20 minutes of heat.

9. Fill the pot with water to a height a just a bit deeper than the height of the water in the bottles(this way the bottles wont float too much when you place them in the bath). Place thethermometer such that you can safely monitor the temperature. Heat the water to 110F(slightly warmer than a hot spa). During the experiment, continually monitor the temperatureand adjust the burner such that the water temperature is kept relatively constant at 110F. Becareful of steam.

10. Place bottles # 2-5 in the warm water and maintain the temperature between 100 and 120 Ffor ~20 minutes. Bottle # 6 may or may not be placed in the bath, depending upon yourchoice of experimental treatment. Bottle #1 should be left sitting at room temperature (it willserve as a temperature treatment). Monitor the experiment carefully. Do not let the bathtemperature exceed 120F.


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11. After 20 minutes, turn off the burner and remove all of the bottles. Make a quickexamination of the results and note the volume of the balloons (large, medium, small, none),the growth of the yeast medium (much, moderate, little, none). Record these quickobservations in Table 3.2.

Table 3.2. Observations of dependent variables.Bottle Balloon size Yeast growth Other observations/ comments

1

2

3

4

5

6

Figure 3.6. Yeast solution after growth.

12. Use a string to take various measurements of each balloon. Be careful not to dislodge theballoon while you measure it. Record your measurements in Table 3.3.

a) Estimate the diameter of each balloon (when looking at the balloon, diameter is thelinear distance from edge to edge). Since the balloons are closer to ellipsoids (Figure3.5) than spheres, you will need to measure both the long vertical axis parallel to thebody of the bottle and the shorter dimension perpendicular to the bottle body.

b) Wrap a string around the horizontal circumference of the balloon at its fattest point.

The string should be horizontal (i.e. parallel with the ground). Mark the string whereit meets itself and measure the circumference (C) of the balloon in cm by laying thestring along the side of a ruler. Record the length of the horizontal circumference (C)in Table 3.3.

c) Estimate the accuracy of your measurement of the circumference by measuring twice.You should be able to be confidently say that the circumference C of the balloon isyour measured value plus or minus C.


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d) For the long axis radius (R), you cannot wrap the string all the way around because ofthe bottle. In this case, use the string to estimate the distance from the top of theballoon to its base at the bottle neck (i.e. half of the circumference). The radius of theballoon on this axis is R = measured value/3.14. Estimate your uncertainty in makingthis measurement (R). Record these measurements in Table 3.3.

e) Measure the new heights of the yeast solutions. Record in Table 3.3.

Table 3.3. Balloon size and solution height measurements.

Bottle Circumference, C (cm) Radius (long axis, R; cm) New height ofyeast solution (in cm)

1

2

3

4

5

6


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Lab 4: Genetics: From DNA to Heredity

Figure 4.1. DNA uncoiled.


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Lab 4A: DNA Extraction

Materials neededRubbing Alcohol (70% or greater), chilled.Small glass or shot glass

Liquid dish soapTable Salt

Introduction

DNA(deoxyribonucleic acid) is the molecular basis of heredity in all living organisms. DNA islong molecule composed of a chain of nucleotides. These nucleotides form molecular couplessuch that, in its simplest uncoiled state, the DNA chain is similar to a ladder with two parallelchains and nucleotide linkages forming the rungs of the ladder (Figure 4.1).

In prokaryotes,DNA is typically found in circular fragments. In eukaryotes, DNA is found in

super-coiled fragments known as chromosomes. Chromosomes are protected from thebiochemical activities in the cells cytoplasm by a lipid-membraneenclosed sack inside of thecell known as the nucleus(Figure 4.1).

DNA Extraction

How can scientists extract DNA from a cell? The lipid bilayers that make up the cellular andnuclear membranes must be broken without destroying the DNA. The phospholipidsthat makeup cellular membranes have a fatty, hydrophobic(water insoluble) tail and a polar, hydrophilic(water soluble) head. These molecules naturally form a bilayer in which their polar heads stickoutwards towards the aqueous environments of the cell cytoplasm and the extracellular fluid,while their fatty tails intertwine with one another at the core of the membrane.

Figure 4.2. Left. Cell membranes phospholipid bilayer.Right. A phospholipid molecule.


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Soap or detergent molecules are similar to lipids in that they have a fatty tail and a water-solubleside. Thus, like phospholipids, soap forms bubbles (membranes). Soaps can dissolve fats andgreases, thereby being ideal for dissolving away cellular membranes, and are used by scientiststo do exactly this in order to access the non-fatty internal components of a cell. Some over-the-counter detergents also contain enzymes that will dissolve proteins. Neither the soap molecules

nor the protease enzymes will destroy DNA.

To extract the DNA, there must be some means of isolating it from all of the other cellularcomponents. In addition to being a long chain, DNA also has a relatively unique feature in that ithas a slight negative charge. If it is placed in a solution with ionic compounds, it will tend tostick to positive ions. This feature of the DNA molecule is used in extraction techniques.

Activity: DNA extraction protocol

1. Chill isopropyl alcohol (rubbing alcohol) in the freezer.

2. Swish ~4 ml of water around in your mouth for a few minutes. Use your teeth to lightly scrapethe sides of your cheeks. This will dislodge some cheek cells in the water in your mouth. Spitout the water into a small glass.

3. Add three pinches of salt to your solution. Salt is an ionic compound made up of sodium(Na+) ions and chloride (Cl-) ions. In its crystalline form, these two ions stick together, butwhen salt is dissolved in water the two ions separate.

4. Gently add 1 ml of liquid dish soap to the solution. Gently stir this solution for 1minute.Avoid introducing bubbles into the solution.

5. Carefully add 5 ml of the cold alcohol into the solution. Pour it gently down one side of theglass to avoid disrupting the solution. The alcohol should layer on top of the soap/watersolution.

6. Observe carefully. Can you see DNA precipitate out in the layer of alcohol? Use a toothpickor other small rod to investigate the precipitant in the alcohol.

7. Describe what you see. Is the precipitant bubbly or stringy? Does it stick together or does itform many islands? Record these observations in Lab Report 4.


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Lab 4B: Human heredity

Materials neededNone

Introduction

Humans, like many other organisms, are diploid. Being diploid, humans inherit two geneticforms (alleles)of a gene, one from each parent. In this laboratory, you will investigate somecommon human genetic features.

This laboratory is based on the lab manual by Mader. This material is covered in the textbookfor BIO 100.

Genotype and phenotype

The diploid condition means that, in most of the cells in the body, there are two pairs of everychromosome. The two chromosomes in each pair are homologous chromosomes. Homologouschromosomes are typically the same length and shape, and have genesat the same locations.

Genes are regions of chromosomes that are ultimately responsible for the body's anatomy andphysiology. The actual genetic sequence at a gene is an allele. Homologous chromosomesmight have the same genetic sequence at a particular gene, thereby having the same allele for thisgene. In this case, the chromosomes are homozygousfor the gene. Alternatively, homologouschromosomes might differ in the genetic sequence at a gene, thereby representing two differentalleles for the same gene. In this case, the chromosomes are heterozygous.

Any given combination of alleles is the genotype. The phenotypeis the observable result ortraits of the allele combinations. To illustrate these ideas, consider a simplified depiction of eyecolor. Suppose there are two alleles,Band b. The genotypesBBandBbresult in brown eyes,while the genotype bbresults in blue eyes. In this example, theBallele is dominant,becausethe heterozygote (Bb)shows brown color. The ballele is recessive.

Because chromosomes are passed from parent to child, one can predict the relative likelihood ofchildren having certain traits, given that the genotypes of the parents are known. Such ananalysis involves a Punnett square, where the alleles of both parents are combined in allpossible combinations.


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Continuing with the eye color example, suppose a brown-eyed man (Bb)couples with a brown-eyed woman (Bb). This can be described by the following Punnett square (Figure 4.3):

Brown-eyed man (Bb) Brown-eyed woman (Bb)

Figure 4.3. Punnett Square, demonstrating possible genotypes resulting from Bb Bb pairing..

In this example, a common, and generally valid, assumption is that equal numbers ofBand b

sperm cells are produced by the man. Similarly, the woman is assumed to be equally likely toovulate an egg containing aBor ballele. Under these assumptions, the man and woman are 25%likely to produce aBBchild, 50% to produce aBbchild, and 25% to produce a bbchild. Theseare the genotype frequencies. But, becauseBBandBbboth result in brown eyes, the phenotypefrequencies are different: 75% to produce a brown-eyed child and 25% to produce a blue-eyedchild.

For the lab report, you will collect data on three human traits: tongue-rolling, earlobeattachment, and thumb flexibility ("hitch-hiker's thumb").

Man

(Bb)

B

b

B b

Woman(Bb)

BB

(brown)

Bb

(brown)

Bb

(brown)

bb

(blue)


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Tongue-rollingPhenotype R: "roll" (can curl sides of tongue). Genotype: RRorRr.Phenotype r: "no roll" (cannot curl sides of tongue). Genotype: rr.

Figure 4.4. Tongue-rolling. The "roll" phenotype is R (genotype isRRorRr).[Image takenfrom the Internet.]


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Earlobe attachmentPhenotype U: "Unattached." Genotype: UUor Uu.Phenotype u: "Attached." Genotype: uu.

Figure 4.5. Earlobe attachment. [Image taken from the Internet.]A) "Unattached" phenotype is U (genotype is UUor Uu).B) "Attached" phenotype is u (genotype is uu).


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Thumb flexibility ("hitch-hiker's thumb")Phenotype H: "No hitch-hiker." Genotype: HHorHh.Phenotype h: "Hitch-hiker" (last joint of thumb can extend backwards). Genotype: hh.

Figure 4.6. Thumb flexibility. [Images taken from the Internet.]Left: "No hitch-hiker" phenotype is H (genotype isHHorHh).Right: "Hitch-hiker" phenotype is h (genotype is hh).

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