Lab 3

Aseptic Technique

Introduction: Connecting Your Learning

Microorganisms are always present in the air and on laboratory surfaces, benches, and equipment. They can serve as a source of external contamination and interfere with experimental results unless proper techniques are used to prevent contamination. The technique that is most often used to prevent the contamination of culture is called the aseptic technique. This technique is important for the growth, isolation, and identification of microorganisms in the laboratory.

Readings, Resources, and Assignments

Multimedia Resources	Aseptic Technique Video
Required Assignments	Lab 3 Assignment

Focusing Your Learning

Course Competency

1. Utilize aseptic technique for safe handling of microbes.

As you work through this lab, consider the objectives below.

Lab Objectives

By the end of this lab, you should be able to:

1. Identify techniques for aseptic handling, transfer, and disposal of microbial organisms in the lab.
2. Define how to maintain cultures, emphasizing transfer and isolation of microorganisms.

Background Information

Please watch and take notes on this aseptic technique video: Aseptic Technique Video

Aseptic technique
In nature, most microbes are found growing in environments that contain many different organisms. Unfortunately, these mixed cultures are of little use in studying microorganisms because of the difficulty in determining which organisms are responsible for any observed activity. In order to grow and identify the microorganisms, the microorganisms must be isolated from one another in the specimen.

This process is done by transferring the microorganisms from one vessel to another or from culture to various media for maintenance and study. Such a transfer is called subculturing and must be carried out under sterile conditions to prevent possible contamination. The purpose of subculturing is to obtain separate cultures, each containing only one species of microorganism. A culture containing a single unadulterated species of cells is called a pure culture. Pure cultures contain only one type of organism and are suitable for the study of their cultural, morphological, and biochemical properties. This is of extreme importance in preparing and maintaining cultures as well as in microbiological test procedures. To isolate and study microorganisms in pure culture, the microbiologist requires basic techniques such as aseptic technique.

Subculturing enables one to go from a mixed culture plate that contains many different colonies to a pure culture containing just one type of microbe.

This agar plate contains mixed cultures from a swab performed at a hospital on patient elevator buttons and escalator rails.

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by Jnims, CC BY-SA 3.0 , via Wikimedia Commons is licensed under CC BY 4.0.

A blood agar plate containing a of pure culture Staphylococcus

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by Bill Branson – (Edited by Fir0002)(Edited by Drhx), Public domain, via Wikimedia Commons is licensed under CC BY 4.0.

Aseptic technique encompasses many different processes. Aseptic technique includes the use of gloves to prevent contamination from people, the use of heat to kill microorganisms on transfer equipment such as needles or loops, and transfer techniques to isolate microorganisms on culture media.

The following table summarizes basic vocabulary concerning the aseptic discussion.

Term	Definition
Antisepsis	Refers to the killing or removal of microbes on living tissues. Sepsis is bacterial contamination.
Clean	“Clean” has a very restricted meaning in microbiology. Generally it means the removal of dirt or debris superficially. It does not kill or remove all microbes.
Disinfection	Refers to the killing of microbes on inanimate objects or materials (non-endospore-forming).
Germicide/Biocide	A chemical agent that demonstrates killing power against various microbes. -cide = means to KILL (excluding endospores).
Pasteurization	A heating process that reduces the number of spoilage germs and eliminates pathogens in milk and other heat sensitive foods.
Sanitization	Usually used by the food industry. Reduces microbes on eating utensils to safe, acceptable levels for public health. Generally reduces microbial counts.
Static	Processes or chemical agents that inhibit bacterial growth but do not necessarily kill microbes.
Sterilization	Kills or removes all forms of life, including bacterial endospores.

The microbial growth on this plate is the result of contamination. Multiple colonies exhibiting various different cultural characteristics are present.

Creative Commons
by Garnhami, CC BY-SA 4.0 , via Wikimedia Commons is licensed under CC BY 4.0.

Described below are essential steps that one must follow for aseptic transfer of microorganisms.

1. An inoculating needle or loop must always be sterilized by holding it in the hottest portion of the Bunsen burner flame, the inner blue cone, until the entire wire becomes red-hot. An incinerator can be used instead of a Bunsen burner. Then, the upper portion of the handle is rapidly passed through the flame. Once flamed, the loop is never put down but is held in the hand and allowed to cool for 10-20 sec. The stock culture tubes and the tube to be inoculated are held in the palm of the other hand and secured with the thumb. The two tubes are then separated to form a V in the hand.

Preparing to flame a loop

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by Samuel Larson, CC BY 4.0 , via Wikimedia Commons is licensed under CC BY 4.0.

1. The tubes are uncapped by grasping the first cap with the little finger, the second cap with the next finger, and lifting the closures upward. Once removed, these caps must be kept in the hand that holds the sterile inoculating loop or needle, thus the inner aspects of the cap point away from the palm of the hand. They must never be placed on the laboratory bench because doing so would compromise the sterile procedure. Following removal of the closures, the necks of the tubes are briefly passed through the flame and the sterile transfer instrument is further cooled by touching it to the sterile inside wall of the culture tube before removing a small sample of inoculum. The necks of the tubes are flamed to prevent contamination of the tube from the outside environment, to prevent the sterile needle from becoming contaminated if it touches the neck of the tube, and to prevent the bacteria inside the tube from leaving the tube.
2. Depending on the culture medium, a loop or needle is used for removal of the inoculum. Loops are commonly used to obtain a sample from a broth culture. Either instrument can be used to obtain the inoculum from an agar slant culture by carefully touching the surface of the solid medium in an area exhibiting growth so as not to gouge into the agar. A straight needle is always used when transferring microorganisms to an agar deep tube from both solid and liquid cultures.
3. The cell-laden loop or needle is inserted into the subculture tube. In the case of a broth medium, the loop or needle is shaken slightly to dislodge organisms; with an agar slant medium, it is drawn lightly over the hardened surface in a straight or zigzag line. For inoculation of an agar deep tube, a straight needle is inserted to the bottom of the tube in a straight line and rapidly withdrawn along the line of insertion. This is a stab inoculation.
4. Following inoculation, the instrument is removed, the necks of the tubes are reflamed, and the caps are replaced on the same tube from which they were removed.
5. The needle or loop is again flamed to destroy remaining organisms.

The following are examples of how to perform aseptic technique to transfer microbes:

Creative Commons by Microbiology: A Laboratory Manual 6th ed. is licensed under CC BY 4.0.

Creative Commons by Microbiology: A Laboratory Manual 6th ed. is licensed under CC BY 4.0.

Using a subculturing process, microorganisms in the specimen are repeatedly transferred from culture to culture until colonies appear that are separate from one another. Colonies are individual, macroscopically visible masses of microbial growth on a solid medium surface, each representing the multiplication of a single organism. Once the discrete colonies are obtained, an aseptic transfer is made onto nutrient agar slants for the isolation of pure cultures.

The techniques commonly used for isolation of discrete colonies initially require that the number of organisms in the inocolum be reduced. The decrease in the population ensures that, following inoculation, individual cells will be sufficiently far apart on the surface of the agar medium to cause a separation of the different species present. The following are subculturing techniques that can be used to accomplish this necessary dilution and isolation of colonies.

The streak-plate method is a rapid qualitative isolation method. It is essentially a dilution technique that involves spreading a loopful of culture over the surface of an agar plate. In the streak-plate method, a loop is used to streak the mixed sample many times over the surface of a solid culture medium in a Petri plate. The process of streaking the loop repeatedly over the agar surface causes the bacteria to fall off the loop one by one and to be distributed over the agar surface, where each cell develops into a colony. Although many types of procedures are performed, the four-way or quadrant streak will be described.

Flaming a loop: The loop is sterilized by holding it in the hottest portion of the Bunsen burner flame, the inner blue cone until the entire wire becomes red-hot. Then it must be cooled 10-20 seconds before it can be used.

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by CSIRO, CC BY 3.0 , via Wikimedia Commons is licensed under CC BY 4.0.

1. Using a flamed and cooled loop, place a loopful of culture on the agar surface. Flame and cool the loop, then drag it rapidly several times across the surface of area.

   To avoid digging into the agar as one streaks the loop over the top of the agar, one must keep the loop parallel to the agar surface.

Step 1 to streak a plate

Creative Commons https://commons.wikimedia.org/wiki/File:Streak_pla… by PNG: Wikipedysta:Reytansvg: Marek M (talk) 11:44, 3 May 2011 (UTC), Public domain, via Wikimedia Commons is licensed under CC BY 4.0.

1. Reflame and cool the loop and turn the Petri dish 90º. Then touch the loop to a corner of the culture in area 1, and drag it several times across the agar in area.

   The loop should never enter area 1 again.

Step 2 to streak a plate

Creative Commons https://commons.wikimedia.org/wiki/File:Streak_pla… by PNG: Wikipedysta:Reytansvg: Marek M (talk) 11:44, 3 May 2011 (UTC), Public domain, via Wikimedia Commons is licensed under CC BY 4.0.

1. Reflame the loop and cool the loop, and again turn the dish 90º. Streak area 3 in the same manner as area 2.

Step 3 to streak a plate

Creative Commons https://commons.wikimedia.org/wiki/File:Streak_pla… by PNG: Wikipedysta:Reytansvg: Marek M (talk) 11:44, 3 May 2011 (UTC), Public domain, via Wikimedia Commons is licensed under CC BY 4.0.

1. Without reflaming the loop, again turn the dish 90º and then drag the culture from a corner of area 3 across area 4, using a wider streak. Do not let the loop touch any of the previously streaked areas. The flaming of the loop at the points indicated is to affect the dilution of the culture so that fewer organisms are streaked in each area, resulting in the final desired separation.

Step 4 to streak a plate

Creative Commons https://commons.wikimedia.org/wiki/File:Streak_pla… by PNG: Wikipedysta:Reytansvg: Marek M (talk) 11:44, 3 May 2011 (UTC), Public domain, via Wikimedia Commons is licensed under CC BY 4.0.

The following pictures are examples of the streak-plate method:

Streaking a plate using an inoculation loop

Creative Commons https://commons.wikimedia.org/wiki/File:Utstryksme… by Lucas R, CC BY-SA 4.0 , via Wikimedia Commons is licensed under CC BY 4.0.

Campylobacter jejuni colonies isolated on blood-free, charcoal based selective medium (CSM).

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by Kubo Michal is licensed under CC BY 4.0.

The spread-plate technique requires a previously diluted mixture of microorganisms to be used.

Serial dilution dilutes a fixed volume of cells mixed with dilution solution using the previous dilution as an inoculum. The result is dilution by an exponentially growing factor. (modification of work by “Leberechtc”/Wikimedia Commons)

Creative Commons https://openstax.org/books/microbiology/pages/9-1-… is licensed under CC BY 4.0.

To make a spread plate, the cells are evenly spread over the surface of a solid agar medium using a sterile, L-shaped bent rod while the Petri dish is rotated. (This can be accomplished while the plate is spun on a lazy Susan-type turntable). The step-by-step procedure for this technique is as follows:

1. Place the bent glass rod into the beaker and add a sufficient amount of 95% ethyl alcohol to cover the lower bent portion.
2. With a sterile loop, place a loopful of culture in the center of the nutrient agar plate (that has been placed on the turntable if using the turntable). Alternatively, pour or pipette sample onto the agar. Replace the cover.
3. Remove the glass rod from the beaker, and pass it through the Bunsen burner flame with the bent portion of the rod pointing downward to prevent the burning alcohol from running down one’s arm. Allow the alcohol to burn off the rod completely. Cool the rod for 10-20 sec.
4. Remove the Petri dish cover and if using the turntable, spin the turntable.
5. Lightly touch the sterile bent rod to the surface of the agar and move it back and forth to spread the culture evenly over the agar surface.
6. Replace the cover. Immerse the rod in alcohol and reflame.

Spread plat

Flag question: Question 1Question 

1. What is the largest component of Earth’s atmosphere

Group of answer choicesOxygen

Nitrogen

Water Vapor

Carbon Dioxide

Flag question: Question 2Question 

2. The strongest greenhouse gas

Group of answer choicesMethane

Dust

Carbon Dioxide

Water Vapor

Flag question: Question 3Question 

3. A temperature inversion is characterized by air temperature that

Group of answer choicesincreases with altitude

nobody knows

stays the same

decreases with altitude

Flag question: Question 4Question

4. Atmospheric pressure at sea level is generally

Group of answer choiceshow would I know?

lower than in the mountains

stays the same as in the mountains

higher than in the mountains

Flag question: Question 5Question 

5. It’s a cool and cloudy morning at Long Beach. The temperature is 62 and the dewpoint is 59. A pilot takes off from Long Beach airport and notices the temperature “jumps” to 85 degrees at an altitude of 3,000 ft along his initial ascent where the sun is shining and the sky is a stunning blue above a white ocean of clouds. This weather scene is technically known as a

Group of answer choicescyclogenesis

offshore wind

temperature inversion

sign of convective instability

Flag question: Question 6Question 

6. What heats up and also cools down slower?

Group of answer choicesland

land and water

water

neither

Flag question: Question 7Question

7. A typical “storm” is usually known as?

Group of answer choicesa dynamic high

a thermal low

a thermal high

a dynamic low

Flag question: Question 8Question

8. The ITCZ or Inter Tropical Convergence Zone is a good example of a

Group of answer choicescold frontal system

warm and dry airmass

mid latitude cyclone

global equatorial zone

Flag question: Question 9

9. It’s 40 degrees Fahrenheit in the Great Basin of Nevada  on a particular day in November. The surface winds are blowing out of the area in response to this cold weather, what kind of a weather system is this indicative of (over the Great Basin)?

Group of answer choicesdynamic low

thermal high

dynamic high

thermal low

Flag question: Question 10

10. It’s 95 degrees in Glendale and 65 degrees in Santa Monica, given what we have learned so far about weather and local winds what kind of a wind might you expect between Santa Monica and Glendale (choose the best answer)?

Group of answer choiceshurricane

sea breeze

land breeze

Chinook

Flag question: Question 11

11. A sea breeze is an example of

Group of answer choiceshurricane

onshore flow

tornado

offshore flow

Flag question: Question 12

12. The following chart indicates areas of wind energy at an altitude of about 30,000 feet or so above sea level. 

This jet stream is located

Group of answer choicesbetween Asia and California

over Alaska

across the north pole

over the equator

Flag question: Question 13

13. The jet stream in the previous chart is what would normally be expected during 

Group of answer choiceswinter

summer

climate change

hurricane formation

Flag question: Question 14

14. During the winter the jet stream typically 

Group of answer choicesdisappears

gets stronger and further south

gets weaker and further north

is confined to the Arctic

Flag question: Question 15

15. The strongest jet stream energy is associated with 

Group of answer choiceswarm northern latitudes (Arctic) and cold southern latitudes (equatorial region)

cold northern latitudes (Arctic) and warm southern latitudes (equatorial region)

equal temperatures globally

climate change

Flag question: Question 16

16. California’s rain and mountain snow that is common during the winter season is usually a result of 

Group of answer choicesstorms being delivered by a strong jet stream

Santa Ana winds with strong high pressure

the sea breeze

weak jet stream energy and warm Arctic temperatures

Flag question: Question 17

17. During the summer the jet stream typically 

Group of answer choicesaffects California the most frequently

strenthens and heads toward the equator as temperatures warm up

weakens and heads back toward the Arctic as temperatures warm up

stays the same as during the winter

Flag question: Question 18

18. Here is a chart of Arctic sea ice concentration since the early 2000s until 2019. There is an abrupt curve exhibited on this graph with Arctic sea ice volume sharply declining (and a lot of ice melting) between April until September. This is a result of  

Group of answer choicesmanipulated data as there has not been any Arctic sea ice in the summer for nearly a decade

the sun being directly overhead and shining on the Arctic continuously with 24-hour sunlight and no sunset and no night for 6 months straight at the North Pole

global warming also known as climate change

instrumentation error as it is very difficult to get accurate readings that far north in the world

Flag question: Question 19

19. Some of the most extreme weather to have ever hit California with multi-decades-long drought, searing heat characterized by unbelievable temperature readings (133 degrees in Santa Barbara), devastating floods that left huge parts of the state under water for up to 6 months and more happened during the 

Group of answer choices2000s

mid 1800s

early 1900s

late 1990s

Flag question: Question 20

20. The fact that heat and cold go through fluctuations, with some areas hotter and others colder, some years warmer and others colder and by extension some places drier while others wetter is a result of

Group of answer choicesmysterious processes that have no explanation

fake news since the weather is always similar

increase in global greenhouse gas emissions like Carbon Dioxide

changes in atmospheric pressure configurations that result in what we call weather

Flag question: Question 21

21. When the air is warmer near the surface and colder in the upper atmosphere, oftentimes evident by the development of upward rising cumulus clouds, the conditions are said to be

Group of answer choicestectonically active

the result of a temperature inversion

stable

unstable

Flag question: Question 22

22. Lightning, heavy rain, strong winds, hail and even tornadoes are the result of 

Group of answer choicesatmospheric stability

drought

convection

the marine layer inversion

Flag question: Question 23

23. On a particular day not too long ago a cold pocket of air aloft, characterized by temperatures of -23 C (-9 F) at 18,000 feet moved over southern California, associated with a late-season trough of low pressure. During the late morning to early afternoon temperatures were still in the mid to upper 50s under overcast skies with drizzle and even light rain falling around downtown Los Angeles. Temperatures were similarly cool and it was also cloudy in the San Fernando Valley. Meanwhile, skies were partly cloudy across the high desert were temperatures were generally in the mid to upper 60s at the same time. Given this information where would you expect the greatest instability was developing?

Group of answer choicesLos Angeles basin

nowhere

San Fernando Valley

high desert

Flag question: Question 24

24. Where would you expect the greatest chance of thunderstorms to form that afternoon? 

Group of answer choiceshigh desert

nowhere

Los Angeles basin

San Fernando Valley

Flag question: Question 25 pts

25. If there is a mid-latitude cyclone with cold air aloft moving in, the temperatures near the surface are warmer than above, there is adequate moisture available for cloud formation, the winds at ground level are coming in from the Southeast at 15 knots, as altitude increases the wind is observed to be increasing as well changing direction to South at 5,000 feet , then Southwest at 18,000 feet with a strength of 60 knots. The Doppler radar begins to pick up on a developing and intensifying “cell” with light green around the edges and yellow, orange and even red toward the middle. If you were a forecaster you would begin to consider the possibility of

Group of answer choicestornadoes

a hurricane

Santa Ana winds

a blizzard

Flag question: Question 26

26. Los Angeles rainfall has been 

Group of answer choicesdramatically decreasing with permanent drought conditions now the rule

too complicated to think about

continuously increasing with more rain now than ever before

going through cycles of some years having more, others having less and others seeing about average

Flag question: Question 27

27. The notion that tornadoes do not occur in California is 

Group of answer choicessomething that everyone knows because this is earthquake territory

true because the jet stream stays away

true because there are mountains and valleys

a myth

Flag question: Question 28

28. When the temperature and dewpoint temperature are not equal 

Group of answer choicesthe air is not saturated

it gets much cooler

the air is saturated

clouds and fog form

• List the forms of nitrogen in the nitrogen cycle in order of most oxidized to the most reduced form. [2]
• What are the two key enzymes involved in nitrogen fixation? How does molecular oxygen affect the reductase complex? How is this overcome? [3]
• Compare how glutamate is formed in plants and bacteria versus its formation in animals. [2]
• a) What two amino acids normally supply the nitrogen required for amino acid and nucleotide synthesis? b) What molecule i s a common intermediate in the synthesis of several amino acids AND in nucleotide synthesis? [2]
• a) How is glutamine used in nitrogen metabolism?
  b) Why is the activity of glutamine synthetase tightly regulated? [2]
• What is meant by the term “essential amino acid”? List the six primary precursors used to derive the 20 common amino acids. [2]
• Describe the role of PLP in the biosynthesis of serine, glycine and cysteine. [2]
• List the amino acids synthesized from oxaloacetate and pyruvate. Which amino acids are essential and which are non-essential? [3]
• In what way is the role of ATP in histidine biosynthesis unusual? Propose a possible fate for the inorganic phosphate released at step 8 in histadine biosynthesis. [2]
• Briefly describe the regulatory mechanisms involved in purine and pyrimidine nucleotide synthesis. What is the role of aspartate transcarbamoylase? [3]
• Describe the functions of phosphocreatine and glutathione. [2]
• What do all amino acid decarboxylases have in common? Which of the following is not a conversion reliant upon a decarboxylase? [2]
  • dopa to dopamine
  • glutamate to GABA
  • tryptophan to 5-hydroxytryptophan
• a) Which molecules contribute the nitrogen atoms for purine biosynthesis?
  b) Which reactions in the de novo synthesis of purine nucleotides require energy expenditure? [3]
• Describe the similarities and differences in the de novo synthetic schemes of purines and pyrimidines. [2]
• What happens to purine biosynthesis when excessive AMP accumulates? [2]
• How are nucleotide monophosphates are converted to nucleotide triphosphates? [2]
• How are deoxyribonucleotides are formed from ribonucleotides? [2]
• How do ATP and low and high concentrations of dATP affect the activity of ribonucleotide reductase? [2]
• Using your text and any available web resources, identify a genetic disease that results from an anomaly associated with the biosynthesis of amino acids, nucleotides or related molecules. Provide the name of the disease, its exact biochemical effect on the pathway(s), the resultant physiological and symptomatic aspects, and how it might be treated. [5]
• Locate and read the following article which has implications on the de novo synthesis of guanosine nucleotides . Answer the questions below. [5]

  Murali Dhar TG, Shen Z, Gu HH, Chen P, Norris D, et al. (2003) Bioorganic & Medicinal Chemistry Letters, 13 (20): 3557-3560.

• Specifically what reaction does inosine monophosphate dehydrogenase catalyze?
• With respect to the novel small molecule inhibitors of inosine monophosphate dehydrogenase, what general purpose is sought or served by the carbamate side chain?
• What metal is commonly used in the catalysis of the reactions described in this article?
• Why would the scientists be interested in identifying or developing novel small molecule inhibitors of inosine monophosphate dehydrogenase?
• If you were to take on a follow-up study to this research, what might you investigate?

1.Describe the difference between endocrine and paracrine hormones.

2. What are the possible fates of acetyl CoA produced by the liver?

3. What types of lipids are stored in adipocytes? What triggers mobilization of these lipids?

4. List the compounds used as energy sources by each of the following:

a) Skeletal muscle

b) Cardiac muscle

c) Brain

5. Describe how epinephrine coordinates enzyme activity in the gluconeogenic and glycogen breakdown pathways.

6. At the molecular level, what is the effect of glucagon on cell metabolism?

7. What are the effects of epinephrine on each of the following aspects of metabolism:

a) Glycogen breakdown

b) Glycolysis

c) Glucagon secretion

d) Insulin secretion

8. During conditions of fasting or starvation, what is the limiting factor in using citric acid cycle intermediates for gluconeogenesis?

9. Describe the feedback loop observed in insulin secretion.

10. During starvation what happens to the acetyl co-A made available from stored fats?

11. How are the cellular effects of insulin mediated? How does insulin regulate the activity of glycogen phosphorylase?

12. Adrenalin is stored in and released from membrane bound vesicles. Why are testosterone and estrogen not stored in this manner?

13. Describe the differences between Type 1 and Type 2 diabetes and the kinds of therapy used to control each.

14. Why are peptide hormones are initially synthesized as inactive precursors (prepro- or pro-hormones) and processed to the active hormone?

15. Compare and contrast the mechanisms and locations of the effects of peptide and amine hormones and steroid hormones. (Answer in table form if you wish.)

16. Why are the effects of steroid and thyroid hormones slower in action and lengthier in duration than other types of hormones?

17. What factors are released from the hypothalamus, and what cells do they target?

18. Why are the hormones of the anterior pituitary gland often described as tropic?

19. Cells of the islets of Langerhans are found in the _____________. Glucagon is produced by the ____ cells and insulin by the ____ cells.

20. Which hormones are catecholamines? When acting as hormones, from where are they secreted? Where else might these molecules be found?

21. Briefly describe the major actions of the catecholamines on carbohydrate and lipid metabolism.

22. Describe the general pathways and end products of carbohydrate and lipid metabolism in each of the following mammalian tissues:

a) Liver

b) Adipose

c) Muscle (skeletal and heart)

d) Brain tissues

e) Blood

23. Locate and read the following article. Answer the questions below.

Sandoval DA and Davis SN. (2003) Journal of Diabetes and its Complications, 17 (2): 108-113.

• What exactly is leptin, and how does it relate to the biochemistry of metabolism?
• How do researchers often experimentally induce hypoglycemia?
• Describe how exercise, a stressor, affects the secretion of leptin.
• How might activity of the sympathetic nervous system affect plasma leptin secretion on a molecular level?
• A major function of leptin may be to switch fuel utilization to fat from carbohydrates. T/F

Module 6 Lab: Human mate choice

In many human cultures there tends to be agreement over what constitutes attractiveness – with people from different societies often agreeing that a given woman or man is ‘attractive’.  It is less clear, however, what actual traits observers use to make this judgement.  In this week’s lab, we are going to test a number of hypotheses to determine if there is a good way to subjectively measure attractiveness.

Background

Sexual selection and good genes hypothesis:  Many species display the phenomenon of sexual selection – where males display costly ornaments or behaviors (although in some cases it is females that display these costly ornaments or behaviors).  According to parental investment theory, the gender that has lower intrinsic investment in reproduction is forced to compete for the attentions of the gender with the higher investment (Trivers, 1972).  There is still a fair amount of theoretical discussion concerning the costs and benefits of sexual selection.  One perspective, the ‘good genes’ concept, suggests that costly ornaments are essentially ‘honest signals’ that the bearer is carrying high quality genes.  An animal that is capable of maintaining a large feather display or complicated nest-building behavior must also be generally healthy and the carrier of desirable genetic qualities. 

Humans are not exempt from sexual selection theory.  Males and females are dimorphic in size and also in secondary sexual characteristics.  The human face contains secondary sexual traits that include facial features that may develop or increase in size at puberty.  Humans make judgements about the attractiveness of prospective partners based in part on these facial cues.  An attractive partner may elicit greater efforts at courtship or more costly displays to gain the attentions of the would-be mate.  But how do humans make these judgements about attractiveness?

Facial Symmetry Hypothesis:  One hypothesis regarding human attractiveness is facial symmetry.  Symmetry is often correlated with genetic heterozygosity in many animals, including humans (Thornhill and Gangestad, 1993).  Such heterozygosity may be linked to parasite resistance as well as other diverse positive traits and therefore symmetry may be an indicator of ‘good genes’.  There is evidence that facial symmetry is positively correlated with scores of attractiveness (Grammer & Thornhill, 1994; Fink et al. 2006), and it may also act as a cue to an individual’s personality characteristics (Fink et al., 2006). 

Averageness Hypothesis: Another hypothesis is the averageness hypothesis (Thornhill & Gangestad, 1993).  Based on this idea, researchers compiled photos of different people.  They found that the more people’s faces were averaged together, the higher the attractiveness score became. Thornhill and Gangestad (1993) suggest that facial averageness is attractive because of its association with heterozygosity.  It should be noted that the facial symmetry hypothesis and averageness hypothesis are not mutually exclusive.

Questions:  In order to investigate these questions, you will be utilizing an interactive website to rate human faces for attractiveness and also to create average faces (in which individual faces are blended together).

Instructions:

Access the website at: http://www.faceresearch.org/demos/average

To create averages, select faces you want to average and they will be show boxed in yellow.  To unselect an image, just click it again.

When you’ve selected the ones you want in your selection, click ‘average’.  Between trials, click the reset button to clear your previous selections.

Assignment instructions:

Assign attractiveness scores to the first 20 faces of each sex on a scale from 1 – 10.

Of the 20 faces, choose three women you assigned the lowest scores, and average their faces. Score the new composite face.

Of the 20 faces, choose three women with scores close to 5 and average their faces. Score the result

Of the 20 faces, choose three women with the highest scores and average their faces. Score the resulting face.

Average all 20 female faces. Score the resulting face.

Repeat steps 2-5, using male faces.

Here is a video example of me walking through the lab:

Report Instructions:  You will need to submit a formal lab report.  The report should be in a word document with the following sections:

Introduction

An introduction containing a description of the basic questions and the premise (ie, what are the researchers testing with their facial averaging software?). Be sure to write and include both a description of each hypothesis (symmetry and averageness) as well as your research questions (Links to an external site.) https://writingcenter.gmu.edu/guides/how-to-write-… related to these.

Materials and Methods

In paragraph format and in past tense, describe the materials you needed and the methods you used to complete this lab. Similar to past modules, we understand this is an online lab so this section is a little difficult, but remember, someone (who is not in this class) should be able to complete the lab based on what you write here so what should you include?

1. Results
2. You should summarize your findings in a series of data tables AND graphs.  
3. Submit a data table with your results summarized. Write a summary (in a word document) answering the following:
4. Compare scores between the original faces and the average faces you created. How do they differ?
5. Compare the scores for the composite faces across the low, medium, and high scoring categories.
6. Does the score the average face change with how many individual faces are used to create it?

Submit a graph or graphs illustrating your data

For example, you might include a bar graph (or series of bar graphs) comparing the average attractiveness of the sets of three faces you selected (less attractive, medium attractiveness, and very attractive) before and after averaging.  

Discussion

Finally, you should summarize your findings in your lab report.  

Was the ‘averageness’ hypothesis supported?

• Was the ‘facial symmetry’ hypothesis supported?

References

Fink, B, et. al, (2006).  Facial symmetry and judgements of attractiveness, health, and personality.  Personality and Individual Differences 41: 491-499

Grammer, K, Thornhill, R (1994).  Heritable true fitness and bright birds: A role for parasites?  Science 218: 384-387

• Thornhill, R, Gangestad, S (1993).  Human facial beauty: Averageness, symmetry and parasite resistance.  Human Nature 4: 237-269

Trivers, R. (1972).  Parental investment and sexual selection.  In B. Campbell (Ed.) Sexual selection and the descent of man, 1871-1971.  (pp 136-179).  Chicago. IL