Category: My Classroom Material

Ink Chromatography

Chromatography of Inks

Introduction:

One of the main jobs of biochemists is to unravel the complexities of chemical compounds and reduce them to their individual components.  The term chromatography comes from two Greek words, “chromat” meaning color and the word “graphon” meaning to write.  Separation of the components of chemical compounds can be done by using several methods. Liquids can be separate by High Performance liquid Chromatography (HPLC), while the components of gases are separated by Gas Chromatography.  Chromatography is a method for analyzing complex mixtures (such as ink) by separating them into the chemicals from which they are made. Chromatography is used to separate and identify all sorts of substances in police work. Drugs from narcotics to aspirin can be identified in urine and blood samples, often with the aid of chromatography.

Chromatography was first used to separate pigments (colors) in leaves, berries, and natural dyes. Paper chromatography is a technique used to separate, isolate, and identify chemical components of a compound. In paper chromatography, the solid surface is the cellulose fibers in the chromatography paper.  A solvent or developer (water, alcohol, or acetone) is placed in the bottom of the chromatography chamber. The paper acts as a wick to pull the solvent up the paper. The solvent front will “wick” up the chromatography paper by capillary action.  A minute drop of the ink or chemical mixture to be separated is placed near the bottom of the strip of chromatography paper, but slightly above the level of the solvent in the chamber.  As the solvent passes over the drop of ink, the components of the ink dissolve in the solvent. Because the components of the ink do not all dissolve at the same rate, as the components of the mixture move upward, they show up as colored streaks.  The separated substances on the chromatography paper form a color pattern called a chromatogram.

To determine the rate of migration for each pigment or component of the ink, the Rf value for each pigment must be calculated. The Rf value represents the ratio of the distance a pigment moved on the chromatogram relative to the  distance the solvent front moved. Each pigment or compound will have a unique Rf value that scientists can use to identify the substance. The Rf value is calculated using the following formula:

Rf = distance traveled by the compound / distance traveled by the solvent

Objective:

Use the process of paper chromatography to separate the pigments in various markers and then determine the Rf value for each color on your chromatogram.

Materials:

Plastic vials, paper clips, markers in assorted colors, chromatography paper, scissors, pencil

Procedure:

  1. Obtain chromatography vials and chromatography strips, and different color markers so that each person in the group will have two chromatograms.
  2. Cut one end of the chromatography strip to a point. The bottom of the point will mark the starting point for movement of the solvent (H2O).
  3. About 2.0 centimeters from the bottom of the strip, draw a faint horizontal line with pencil. This will mark the starting point for measuring the migration distance of each color.
  4. Using a different color marker for each strip, drop a dot of ink on the center of the horizontal pencil line.  Let this dry a moment & then add more ink to the dot.
  5. Add a small amount of water to the bottom of the chromatography chamber. (The ink dot should be ABOVE the surface of the water.)
  6. Straighten a paper clip and poke a hole through the top of your chromatography strip
  7. Use the paper clip to hang the strip in your chamber. (The straighten paper clip will lay across the top of the chamber.)
  8. MAKE SURE THE TIP OF THE STRIP BUT NOT THE INK IS IMMERSED IN THE WATER!
  9. Notice the separation of the ink as both the solvent and ink travel up the chromatography strip.
  10. Once the solvent front has neared the top of the strip, remove the strip from the chamber and lay it on a piece of paper towel.
  11. Immediately mark the solvent front with a faint pencil line.
  12. Immediately mark the leading edge of each color with an “x”.
  13. Measure, in millimeters, the distance the solvent migrated from the tip of the strip to your solvent front pencil line.
  14. Measure, in millimeters, the distance each color migrated from the point of origin (pencil line where the ink dot was placed) to the leading edge of the color (marked with an “x”.
  15. Record all data in Data table 1.
  16. Calculate and record the Rf value for each color using the formula below.

Rf = distance traveled by the compound / distance traveled by the solvent

Data Table 1

 

Color pen/marker used:

Separated colors
(list top of strip to bottom) 		Distance each color traveled

(mm)

Distance solvent (H2O)
(mm) 		Rf Value for each color

(Distance color traveled / Distance solvent traveled)

       
       
       
       
       
       
       
       

 

 

 

Color pen/marker used:

Separated colors
(list top of strip to bottom) 		Distance each color traveled

(mm)

Distance solvent (H2O)
(mm) 		Rf Value for each color

(Distance color traveled / Distance solvent traveled)

       
       
       
       
       
       
       
       

 

 

Questions:

1. Which color of marker did you use?

2. which color separated out first from your ink dot?

3. Why did the inks separate?

 

4. What was your solvent?

5. If you had used markers that weren’t water-soluble, how would you have had to change this lab?

 

6. Why did some inks move a greater distance than others?

 

7. How do scientists use paper chromatography in their investigations?

 

 

Insect Collection

Insect Collection
click here for Microsoft Word copy

Insects are invertebrates with three pairs of legs, usually  two pairs of wings, one pair of antenna, jointed appendages, and three distinct body regions — head, thorax, & abdomen. Insects belong to the largest phylum of animals known as arthropods.  Many small arthropods are mistaken for insects such as spiders, ticks, millipedes, & centipedes. Although some insects may sting or bite, insects play an important role in nature as a food source for other animals and  as plant pollinators.  

By doing an insect collection, you can, not only learn beneficial and harmful insects common to your area, but you will also learn structural modifications of various insects that have enabled them to survive & become such a successful and diverse group of animals..   You will also learn to use taxonomic keys to identify organisms.   

     In order to properly do an insect collection, several techniques must be learned including how to correctly collect, kill, pin, spread, label, and display your organisms.  The following instructions have been modified for a high school biology classroom.

Insect Orders PowerPoint

Materials needed for collecting:

  • insect net
  • several kill jars with killing agent (nail polish remover works)
  • notebook
  • pencil
  • tweezers
  • several clean baby food jars (these will be holding jars)
  • equipment bag

Good Web sites for identifying Insects:

Bug Guide 

Insect Identification 

Key to Ten Insect Orders

North American Insects

How to make an insect net:      

  1. Bend the triangular part of a wire coat hanger until it forms a circle.
  2. Carefully straighten the wire hook. (A)
  3. Untwist the “neck”. (B)
  4. Sew netting, cheesecloth, or sheer curtain material to form a bag with a tapering end.
  5. Sew a hem at the top end of the bag leaving an opening for the wire hanger.
  6. Thread the wire hanger through the hem of your bag & then twist the wires together.
  7. Use plenty of heavy gray tape to tape the twisted wire securely to the end of a broom handle or wooden dowel.

How to make a kill jar:
 (YOU NEED A SEPARATE JAR FOR BUTTERFLIES & MOTHS SO MAKE 2 JARS)

  1. Use a clean, glass or plastic jar with STRAIGHT SIDES.
  2. Write a poison label and tape this to the front of the jar with clear tape. (KEEP THIS JAR AWAY FROM SMALL CHILDRREN)
  3. Tape the bottom of glass jars with heavy gray tape to protect them from breaking if they are dropped.
  4. Place a 2″ – 3″ layer of cotton balls in the bottom of the jar.
  5. Cut a piece of corrugated cardboard the same diameter as the inside of the jar to fit over the cotton balls.
  6. Carefully punch several small holes in the cardboard with an ice pick.
  7. Charge the jar by adding polish remover to the cotton balls.
  8. Immediately place the cardboard circle on top of the cotton balls & PLACE THE LID ON THE JAR. (ONLY REMOVE THE LID TO ADD OR REMOVE INSECTS!)
  9. Keep the inside of the jar moisture free so insects won’t discolor & replace the cotton & cardboard as needed.
  10. DO NOT STORE DEAD INSECTS IN YOUR JAR AS THEY WILL DECAY & SMELL!!!!!
  11. READ PINNING INSTRUCTIONS & PIN INSECTS AS SOON AS THEY ARE DEAD!!!

https://biologyjunction.com/images/6892f011.gif     http://extension.entm.purdue.edu/401Book/images/collect/fig7.jpg

Remember to  RECHARGE THE JAR PERIODICALLY if insects do not seem to be dying as fast and NEVER LEAVE THE LID OFF OF YOUR JAR!.

Collecting: 

    Insects are found almost everywhere so look for them on plants, in water, in soil, under rocks, in rotten logs, around lights at night, etc.  Your collection will consist of 20 insects for Biology I and 30 insects for Pre-AP Biology.  Collect only adults in perfect condition to receive credit. As you collect insects, be sure to record the name of the insect or a good description, the date collected, and the place each insect was collected in your notebook. Use different kill jars for butterflies and beetles and never put too many insects in the same kill jar.   Once your insect is dead (not just knocked out), use tweezers to transfer them to a small  baby food jar until you arrive home to pin it.  Don’t leave the insects in these holding jars more than a few hours and never leave insects in kill jars more than 3 to 5 hours because of their brittle bodies.  most insects will die within 30 minutes to one hour in a charged newly charged kill jar.

    When collecting stinging insects, invert the net once the insect is captured and allow the insect to crawl to the tapered end of the net. Carefully grasp the net above this tapered end,  open the kill jar, and put the tapered end of the net with the insect inside the jar. Lay the lid back on top of the jar until the insect is “knocked out”.  Remove the lid and lift out the net with the unconscious insect. Turn the net back over, shake the insect  into the jar, & replace the lid until the insect finishes dying.  If you are allergic to certain insect stings, have another student collect this insect for you.  

Materials for mounting & labeling:

  • tweezers
  • Elmer’s glue
  • insects pins
  • card points
  • insect labels
  • spreading board
  • pinning block (optional)
  • straight pins
  • index cards
  • scissors
  • black ink pin
  • pencil
  • several small vials
  • shoebox with Styrofoam in the bottom
  • notebook
  • paper towels

Pinning insects: 

See your insect notebook for pictures of the proper placement of insect pins through the body of different orders of insects.

  1. Hold the insects by its sides using your thumb & forefinger and firmly push the insect pin through the dorsal or top surface of the insect. The pin should be at a right angle to the insect’s body.
  2. The insect should be LEVEL on the pin with just enough pin extending above the top of the insect so you can now handle the pin and not the insect
  • Beetles are pinned near the front margin of the right wing near the midline
  • Grasshoppers are pinned to the right of the prothorax
  • True bugs are pinned to the right of the scutellum
  • Butterflies, moths, dragonflies, & damselflies are pinned through the middle of the thorax
  • Most other insects are pinned through the thorax to the right of the midline

  1. Place insects on insect pins so their body is horizontal to the pinning surface or Styrofoam.
  2. Gently push the insect within at least 25mm from the top of the pin so that you can pick up the pin without touching the insect.  Make sure all pinned and card pointed insects in your collection are at the same height on the pin.  Two labels will be added below the insect’s body later.
  3. If the abdomen sags, place a small piece of index card below the body on the pin until the insect’s body dries and then remove the card.
  4. Insects with extremely long legs like crane flies or curved antenna & abdomens like ichneumon wasps should be placed on their left side and pinned through the right side of their body in the area of the thorax.

OOPS!  My insects got too dry to pin or How to relax insects: 

It is always wise to pin insects the same day that you collect them because if they dry completely, then they must be relaxed before pinning.

  1. Use a plastic container with a tight fitting lid, and add a layer of sand to the bottom of the container.
  2. Moisten the sand and small amount of bleach or carbolic acid to prevent molding.
  3. Place a paper towel on top of the sand and lay insects on the towel.
  4. Replace the lid and allow to re-hydrate for 1-3 days.
  5. Insects without hairy or scaly coverings such as beetles & grasshoppers, may be dropped into hot (just simmering) water for a few moments to relax them.  If specimens are left in the water too long they will ruin!

What do I do with insects too soft to pin? 

  1. All soft bodied insects such as mayflies, aphids, lice, & termites along with fleas must be kept permanently in preserving fluid in vials.
  2. Use clear, glass vials with tight fitting lids.
  3. Place only one type of insect in each vial and add enough alcohol to cover the insect and the identification labels which will be place inside the vial.
  4. Write vial labels in pencil, not ink!
  5. Place the blank sides of the 2 labels together before dropping them down into the vial so they can be read more easily.

What if the insect is too small to pin & not soft bodied? (card pointing):

  1. Insects too small to be pinned should be mounted on a card point.
  2. Card points are small triangular pieces of white cardboard through which a #3 insect pin is placed.
  3. Points are made using a point punch.  Obtain these points from your teacher.
  4. Lay specimens to be mounted on their left side on paper towel.  The insect’s right side should be up towards you!
  5. Place a # 3 pin through the broad end of a card point.  This is easier if you lay the point on a plastic lid so it doesn’t bend when you thrust the pin through the card point!
  6. Use tweezers to bend the very tip of the card point downwards.
  7. Place a small amount of Elmer’s glue on the paper towel and then touch the bent tip of the point to the glue.
  8. Touch and hold this bent tip with its glue to the right side of the thorax of your insect.  Hold the tip to the insect for at least one minute.
  9. Set the pin up into Styrofoam making sure the glue is dry & the insect’s body is parallel to the pinning surface.

Spreading butterfly & moth wings:  

To prevent butterflies & moths from drying out before wing spreading, place them in small plastic bowls in the freezer.  Be sure to tell your mom!

  1. Wings of butterflies and moths are spread to show venations & markings.
  2. Spreading boards can be bought or made out of Styrofoam or wood to spread wings. The top surface of the board is smooth with a slight upward slant and a central groove. The groove should provide a “snug” fit for the insect’s body & contain a strip of soft material into which insect pins can be placed.
  3. Pin the butterfly or moth as describe in the section on insect pinning.
  4. Cut 2 long, narrow strips of index card to hold down the wings when they are spread.
  5. Place the insect pin into the soft material in the central groove of the spreading board so that the insect’s wings are level with the pinning surface.
  6. Place a straight pin on either side of the insect’s body in the groove so it won’t turn when you start spreading.
  7. Place a strip of the index card over each wing and use 2 straight pins to secure each strip to the board.  Be sure to not pin through the wing!
  8. Never touch your fingers to the upper surface of the wing as scales will be removed.  Always hold or touch this index card strip when spreading the wing.
  9. Use another straight pin to help move the left front wing forward. Place the pin behind the large vein in the forewing up close to the body and gently pull this wing forward until its back edge is at a 90 degree angle with the body.  Still holding your fingers on the cardboard strip, place a second straight pin through the strip (not the wing) up close to the front edge of the wing.
  10. In the same manner move the hind wing forward until a small portion of the hind wing is overlapped by the fore wing.  Use 2 more straights pins to secure the back edge of the cardboard strip.  Again, be sure to not pin through the wings!
  11. Repeat steps 8 – 11 for the right wings of the insect.

Some insects such as the Carolina locust also have unusual markings on  their under wings, so only the right side of these insects should be spread!!!

  1. Allow the wings to dry for several days and then remove the strips, add your labels, and place the insect in your collection.

Writing insect labels:

  1. Each insect will have 2 labels on the pin below the insect’s body.  The top label will be the identification label and the bottom label is the location & collector label.
  2. Obtain labels from your teacher and use black ink only for writing the labels unless placing them in alcohol vials.
  3. The identification label is the top label on the pin below the insect’s body.  It should have the scientific name (genus & species) of the insect on the top line, then the common name of the insect, and the insect’s order on the bottom line.  Remember to capitalize the genus & order and to underline the scientific name!
Musca domestica
Housefly
Diptera

 

  1. The location label goes in the same direction on the bottom of the insect pin.  The location the insect was collected should be written on the top line, then the date the insect was collected, and the name of the collector on the bottom line.  If the collector has a long name, you may write their first initial and their last name.

 

Russellville, Ar.
V – 7 – 14
J. Smith

 

  1. Be sure there is enough room between labels so that both can be read.
  2. Labels should be placed on the pin parallel to the body of a pinned insect or parallel to the point if the insect is card pointed.  Be sure that all labels are readable from the right side when the insect’s head is pointing away from you!!!!

  

Collection Requirements:

Pre-AP Biology  is required to collect 30 insects with a minimum of 12 insect orders

Biology I is required to collect 20 insects with a minimum of 10 insect orders

THE FOLLOWING 8 ORDERS ARE REQUIRED OF ALL BIOLOGY STUDENTS: 

  • Lepidoptera (butterflies & moths)
  • Coleoptera (beetles)
  • Diptera (flies & mosquitoes)
  • Homoptera (cicadas & hoppers)
  • Orthoptera (grasshoppers, crickets,…)
  • Isoptera (termites)
  • Hymenoptera (bees, ants, wasps) 
    • IF YOU ARE ALLERGIC, COLLECT A DIFFERENT ORDER OR AN ANT!
  • Hemiptera (true bugs)

Click here for additional orders

Materials needed to display insects:

  • insect case with lid
  • index cards
  • ribbon, yarn, or string
  • scissors
  • black ink pen
  • straight pins
  • preserved insects (pinned, pointed, & in vials)

Displaying insects:

Remember that your insect collection will not be returned to you, so do not build an expensive case.  Sturdy cases can be made out of 2 cardboard bottoms for cola six packs!

  1. Cases should be no more than 35 by 55 cm in size.  All cases must be sturdy with a lid that can be easily opened for grading.  Remember that the cases will be stacked when you turn them in to me!
  2. If the collection has a clear lid, it must be made of plastic and not glass.
  3. Place a sheet of Styrofoam in the bottom of your case .
  4. Make a label from an unlined index card for the center of your case.  This label should contain your full name, subject, class period, date the collection was turned in to the teacher, number of orders, and number of insects in your collection.  Use straight pins to attach this center card to the Styrofoam. PUT THIS IN THE BOX FIRST!
  5. Cut several small pieces of index card for order labels, and use your black ink pen to write the name of each order  you have in your collection on these.
  6. Arrange insects in the case by order and in rows by descending size (largest to smallest).  Use straight pins to attach the correct order label to the Styrofoam at the top of each row.
  7. Spread out the orders and insects so there are no empty spots in your case.
  8. Cut pieces of yarn or ribbon to separate the orders from each other, and again use straight pins to attach  them to the Styrofoam.
  9. Make sure that all pinned insects are facing the front of your case!
  10. Make sure all identification and collector labels on pins are readable form the right side of the case!!

  

 

Insect

Insects   All Materials © Cmassengale  

Phylum Arthropoda        Subphylum Uniramia          Class Insecta

Characteristics

  • Largest arthropod group
  • Found in freshwater & terrestrial habitats, especially tropical areas
  • Legs, mouthparts, & antenna jointed
  • Body segmented into three sections — head, thorax, & abdomen
  • Six legs & up to two pairs of wings located on thorax
  • Have compound & simple eyes
  • One pair of antennae on head
  • Abdomen has 11 segments
  • Exoskeleton, covering & protecting body, is made of chitin & must be molted to grow
  • Elaborate mouthparts include:
         *  Mandibles – jaws
    *       Maxillae – paired sensory structures that move food to mouth
    *   Labium – lower lip
    *   Labrum – upper lip
    *   Palpi – used for tasting
  • Known as mandibulates
  • Spiracles on abdomen open into tracheal tubes for oxygen & carbon dioxide exchange
  • Tympanic membranes on 1st abdominal segment aid in hearing
  • Thorax divided into 3 sections — prothorax, mesothorax, & metathorax
  • One pair of legs on each thoracic segment
  • Wings located on mesothorax & metathorax
  • Ovipositor located on the end of the abdomen in female insects & used to dig hole & lay eggs

Common Insect Orders

  • Orthoptera – grasshoppers, crickets, & cockroaches 2 pairs of straight wings & chewing mouthparts)
  • Isoptera – termites (feed on wood)
  • Dermaptera – earwigs (pincers on end of abdomen)
  • Anoplura – sucking lice (wingless parasites)
  • Hemiptera – true bugs (have triangular-shaped scutellum & last 1/3 of wings membranous)
  • Homoptera – aphids & cicadas (membranous wings held roof-like over body
  • Ephemeroptera – mayflies (have 2 cerci on tail, membranous wings, & nonfunctional mouthparts in adults)
  • Odonata – dragonflies & damselflies (2 pairs of equal size, membranous wings, strong fliers, feed on other insects)
  • Neuroptera – Dobson flies &  lacewings (2 pairs of membranous wings)
  • Coleoptera – beetles (hard forewings or elytra, membranous hindwings)
  • Lepidoptera – butterflies & moths (powdery scales covered wings
  • Diptera – flies & mosquitoes (one pair of wings, 2nd pair modified into balancing structure called halteres)
  • Siphonaptera – fleas (parasites on birds & mammals, wingless as adults)
  • Hymenoptera – bees, ants, & wasps (stinger on abdomen for protection, may live together in groups, pollinators)

     Click Here for Pictures of Insect Orders

 

Success of Insects

  • Found everywhere except in deep part of ocean
  • Very short life span & rapidly adapt to new environments
  • Small size helps minimize competition in habitats
  • Flight helps escape predators & move into other environments

Environmental Impact

  • Pollinate almost 2/3’s of all plants
  • Serve as food for fish, birds, & mammals
  • Help recycle materials (termites recycle wood)
  • Make useful byproducts such as silk & honey
  • Some spread disease
  • Agricultural pests

Grasshoppers

External Structure

  • Head with antenna, compound eyes, & chewing mouthparts
  • Walking legs on prothorax & mesothorax; jumping legs on metathorax
  • Tarsus are lower leg segments with spines, hooks, & pads
  • Leathery, protective forewings on mesothorax & membranous hindwings for flight on metathorax
  • Covering over thorax called pronotum

Internal Structure
Digestive & Excretory Systems

  • Cutting & chewing mouthparts (labium, labrum, mandibles, & maxillae)
  • Saliva added to food in mouth
  • Esophagus carries food to crop for temporary storage
  • Gizzard has chitinous plates to grind food
  • Midgut (insect’s stomach) has gastric caeca (pouches) to secrete digestive enzymes to break down food
  • Food is absorbed into the body cavity or coelom in the hindgut (composed of the colon & rectum)
  • Malpighian tubules filter chemical wastes from the blood & deposit them in the rectum where they leave through the anus

Circulatory System

  • Open circulation of blood
  • Aorta is the largest blood vessel carrying blood to the body cells
  • Hearts are muscular regions of the aorta in the posterior end of the abdomen that pump blood toward head
  • Blood flows back toward abdomen carrying digested food & re-enters the aorta through openings called ostia

Respiratory System

  • Air enters through openings called spiracles along the sides of the abdomen & enters into tracheal tubes that branch into smaller tracheoles where gas exchange with body cells occurs 
  • Tracheal tubes carry oxygen to body cells & return carbon dioxide to leave the body though spiracles

Nervous System

  • Simple brain, nerve cords, & ganglia 
  • Three simple eyes or ocelli (detect light) & a pair of compound eyes (can detect movement but not images)
  • Tympanic membrane on 1st abdominal segment
  • Pair of antenna contains sense organs for touch, taste, & smell detects sound
  • Sensory hairs found on parts of the body
  • Palpi for taste

Reproductive System

  • Reproductive organs (ovaries & testes) located  in abdomen
  • Male deposits sperm into female’s seminal receptacle
  • Stored sperm fertilizes eggs as they  are released by female
  • Ovipositor on tip of female’s abdomen is used to lay eggs
  • Separate sexes
  • Lay large number of eggs to ensure survival

Development

  • Most insects go through changes in form & size called metamorphosis
  • Some insects such as silverfish don’t go through metamorphosis
  • Incomplete metamorphosis goes from egg to nymph (immature form that looks like adult but without fully developed wings) to adult (3 stages)
  • Instars are growth periods between molts of nymphs & larva
  • Grasshoppers, termites, & true bugs go through incomplete metamorphosis


HEMIPTERAN (TRUE BUG) NYMPH

  • Complete metamorphosis goes from egg to larva (segmented & wormlike) to pupa  to adult (4 stages)


BUTTERFLY LARVA (CATERPILLAR)

  • Butterflies, beetles, & flies go through complete metamorphosis
  • In pupal stage, larval tissues break down & cells called imaginal disk develops into tissues of the adult
  • Cocoon or chrysalis is a protective case formed around the pupa


BUTTERFLY COCOON

  • Metamorphosis controlled by hormones
    * Brain hormone stimulates the release of molting hormone (ecdysone)
    * When juvenile hormone level high, larva molts
    * When juvenile hormone level low, larva pupates
    * When juvenile hormone absent, adult emerges from pupal case
  • Different stages of metamorphosis eliminates competition between larva & adults for food & space
  • Multi-stage life cycle helps insects withstand harsh weather
  • Different stages have different functions (caterpillar/growth & adult/reproduction)

Defense Mechanisms

  • Bombardier beetle sprays noxious chemical


BOMBARDIER BEETLE

  • Wasps & bees can sting
  • Some insects use camouflage to blend into their environments
  • Some insects taste bad & have warning colorations 


PAPER WASP

  • Mullerian mimicry – poisonous or dangerous species have similar patterns of warning coloration so predators avoid all the species (black & yellow stripes on bees & wasps)
  • Batesian mimicry – species that are nonpoisonous or not bad tasting have colorations that mimic other poisonous or bad tasting species (Viceroy butterfly mimics bad tasting Monarch)

Insect Communication

  • Insects may communicate with each other using sound (cricket chirps), light (firefly), or “dances” (honeybee)
  • Pheromones are chemicals released by some insects to attract mates or mark trails

Insect Behavior

  • Insects may be solitary or social
  • Social insects (bees, ants, & some wasps) live together in groups & share work (division of labor)
  • Social insects have a caste system with different individuals doing different jobs
  • Honeybee caste system:
    * Workers
    – sterile females
    – care for queen & feed her honey and pollen
    – make beeswax for hive
    – fan wings to cool hive
    – eat honey
    – collect nectar, pollen, & royal jelly
    – live about 6 weeks
    – nurse bees care for larva
    – secrete royal jelly to feed new queen
    * Drones
    – males
    – mate with queen
    – feed by workers
    – driven out of hive to conserve food during winter
    * Queen
    – reproductive female
    – mate only once but store sperm for up to 5 years in seminal receptacles
    – feed by workers
    – secretes chemical called queen factor that prevents other females from sexually maturing
    – leaves hive with 1/2 the workers if there is overcrowding


HONEYBEE HIVE

BACK

 

Genetic Notes Bi

 

Mendelian Genetics 

 

 

Mendel 1862 Mendel 1868 Mendel 1880
1862 1868 1880

 

Genetic Terminology:

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

Blending Concept of Inheritance:

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

Gregor Mendel:

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

 

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

 

Why peas, Pisum sativum?

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

Picture of Pisum sativum
GARDEN PEA

Mendel’s Experiments:

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

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


  •  Mendel produced pure strains by allowing the plants to self-pollinate for several generations
  • These strains were called the Parental generation or P1 strain
  • Mendel cross-pollinated two strains and tracked each trait through two
    generations (e.g. TT  x  tt )

     

                  Trait – plant height

                  Alleles – T tall, t short

    P1 cross    TT  x  tt

    		 genotype      —    Tt
    t t phenotype    —    Tall
    T Tt Tt genotypic ratio –all alike
    T Tt Tt phenotypic ratio- all alike

     

 

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

 

              Trait – plant height

              Alleles – T tall, t short

F1 cross    Tt  x  Tt

 genotype      —    TT, Tt, tt
T t phenotype    —    Tall & short
T TT Tt genotypic ratio —1:2:1
t Tt tt phenotypic ratio- 3:1

 

 

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

 

Trait   –  Plant Height
Alleles – T  tall, t  short

F2 cross       TT  x Tt

F2 cross       tt  x Tt
T t T t
T TT Tt t Tt tt
T TT Tt t Tt tt
          genotype – TT, Tt           genotype – tt, Tt
          phenotype  –  Tall           phenotype  –  Tall & short
          genotypic ratio  – 1:1           genotypic ratio  – 1:1
          phenotypic ratio – all alike           phenotypic ratio – 1:1

 

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

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

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

 

Traits:      Seed Shape & Seed Color

Alleles:     R round                Y yellow
r wrinkled             y green

 P1 Cross:     RRYY          x     r r yy  

      

ry Genotype:      RrYy
RY RrYy
 Phenotype:      Round yellow seed
Genotypic ratio:      All alike
Phenotypic ratio:      All Alike

 

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

 

 

Traits:       Seed Shape & Seed Color

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

 

 

 

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

 

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

Results of Mendel’s Experiments:

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

 

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

 

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

 

Rr
R r

 

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

 

RrYy
RY Ry rY ry

 

 

Other Patterns of Inheritance:

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

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

 

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

 

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

 

Hardy-Weinberg Problems

 

POPULATION GENETICS AND THE HARDY-WEINBERG LAW

 

The Hardy-Weinberg formulas allow scientists to determine whether evolution has occurred. Any changes in the gene frequencies in the population over time can be detected. The law essentially states that if no evolution is occurring, then an equilibrium of allele frequencies will remain in effect in each succeeding generation of sexually reproducing individuals. In order for equilibrium to remain in effect (i.e. that no evolution is occurring) then the following five conditions must be met:

  1. No mutations must occur so that new alleles do not enter the population.
  2. No gene flow can occur (i.e. no migration of individuals into, or out of, the population).
  3. Random mating must occur (i.e. individuals must pair by chance)
  4. The population must be large so that no genetic drift (random chance) can cause the allele frequencies to change.
  5. No selection can occur so that certain alleles are not selected for, or against.

Obviously, the Hardy-Weinberg equilibrium cannot exist in real life. Some or all of these types of forces all act on living populations at various times and evolution at some level occurs in all living organisms. The Hardy-Weinberg formulas allow us to detect some allele frequencies that change from generation to generation, thus allowing a simplified method of determining that evolution is occurring. There are two formulas that must be memorized:

 

p2 + 2pq + q2 = 1 and p + q = 1

 

p = frequency of the dominant allele in the population
q = frequency of the recessive allele in the population
p2 = percentage of homozygous dominant individuals
q2 = percentage of homozygous recessive individuals
2pq = percentage of heterozygous individuals

Individuals that have aptitude for math find that working with the above formulas is ridiculously easy. However, for individuals who are unfamiliar with algebra, it takes some practice working problems before you get the hang of it. Below I have provided a series of practice problems that you may wish to try out. Note that I have rounded off some of the numbers in some problems to the second decimal place.

PROBLEM #1    You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate the following:

  1. The frequency of the “aa” genotype.
  2. The frequency of the “a” allele.
  3. The frequency of the “A” allele.
  4. The frequencies of the genotypes “AA” and “Aa.”
  5. The frequencies of the two possible phenotypes if “A” is completely dominant over “a.”

PROBLEM #2.    Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) have normal blood cells that are easily infected with the malarial parasite. Thus, many of these individuals become very ill from the parasite and many die. Individuals homozygous for the sickle-cell trait (ss) have red blood cells that readily collapse when deoxygenated. Although malaria cannot grow in these red blood cells, individuals often die because of the genetic defect. However, individuals with the heterozygous condition (Ss) have some sickling of red blood cells, but generally not enough to cause mortality. In addition, malaria cannot survive well within these “partially defective” red blood cells. Thus, heterozygotes tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?

PROBLEM #3.    There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. Sorry. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the four (4%) represent the frequency of the homozygous recessive condition, please calculate the following:

  1. The frequency of the recessive allele.
  2. The frequency of the dominant allele.
  3. The frequency of heterozygous individuals.

PROBLEM #4.    Within a population of butterflies, the color brown (B) is dominant over the color white (b). And, 40% of all butterflies are white. Given this simple information, which is something that is very likely to be on an exam, calculate the following:

  1. The percentage of butterflies in the population that are heterozygous.
  2. The frequency of homozygous dominant individuals.

PROBLEM #5.     A rather large population of Biology instructors have 396 red-sided individuals and 557 tan-sided individuals. Assume that red is totally recessive. Please calculate the following:

  1. The allele frequencies of each allele.
  2. The expected genotype frequencies.
  3. The number of heterozygous individuals that you would predict to be in this population.
  4. The expected phenotype frequencies.
  5. Conditions happen to be really good this year for breeding and next year there are 1,245 young “potential” Biology instructors. Assuming that all of the Hardy-Weinberg conditions are met, how many of these would you expect to be red-sided and how many tan-sided?

PROBLEM #6.    A very large population of randomly-mating laboratory mice contains 35% white mice. White coloring is caused by the double recessive genotype, “aa”. Calculate allelic and genotypic frequencies for this population.

PROBLEM #7.    After graduation, you and 19 of your closest friends (lets say 10 males and 10 females) charter a plane to go on a round-the-world tour. Unfortunately, you all crash land (safely) on a deserted island. No one finds you and you start a new population totally isolated from the rest of the world. Two of your friends carry (i.e. are heterozygous for) the recessive cystic fibrosis allele (c). Assuming that the frequency of this allele does not change as the population grows, what will be the incidence of cystic fibrosis on your island?

PROBLEM #8.    You sample 1,000 individuals from a large population for the MN blood group, which can easily be measured since co-dominance is involved (i.e., you can detect the heterozygotes). They are typed accordingly:

 

BLOOD TYPE GENOTYPE NUMBER OF INDIVIDUALS RESULTING FREQUENCY
M MM 490 0.49
MN MN 420 0.42
N NN 90 0.09

 

Using the data provide above, calculate the following:

  1. The frequency of each allele in the population.
  2. Supposing the matings are random, the frequencies of the matings.
  3. The probability of each genotype resulting from each potential cross.

PROBLEM #9.    Cystic fibrosis is a recessive condition that affects about 1 in 2,500 babies in the Caucasian population of the United States. Please calculate the following:

  1. The frequency of the recessive allele in the population.
  2. The frequency of the dominant allele in the population.
  3. The percentage of heterozygous individuals (carriers) in the population.

PROBLEM #10.    In a given population, only the “A” and “B” alleles are present in the ABO system; there are no individuals with type “O” blood or with O alleles in this particular population. If 200 people have type A blood, 75 have type AB blood, and 25 have type B blood, what are the allelic frequencies of this population (i.e., what are p and q)?

PROBLEM #11.    The ability to taste PTC is due to a single dominate allele “T”. You sampled 215 individuals in biology, and determined that 150 could detect the bitter taste of PTC and 65 could not. Calculate all of the potential frequencies.

ANSWERS