School Science Lessons
Biology experiments
Updated: 2008-08-02
Biology names

Table of contents
9.205 Levels of organization
9.1.0 Study animals
9.2.0 Study populations
9.3.0 Study communities and ecosystems
9.4.0 Chromosomes and DNA
9.6.0 Drosophila experiments, Mendel's laws

9.205 Levels of organization
9.0.1 Kingdom Protista (Protoctista) - heterotrophic protists
9.0.2 Chromista
9.0.3 Heterokontophyta

9.1.0 Study animals
9.1.1 Birds
9.1.2 Chickens and chicken hatching
9.1.3 Sea animals and fish
9.1.4 Insects
9.1.5 Earthworms and flatworms
9.1.6 Amphibians and reptiles
9.1.7 Mammals

9.1.1 Birds
2.1 Bird feathers (Primary)
2.2 Bird sounds (Primary)
2.3 Bird beaks and feet (Primary)
2.4 Different birds (Primary)
2.5 Protect our birds (Primary)
2.6 Care of birds (Primary)
Duck Project

9.1.2 Chickens and chicken hatching
9.11 Study an unfertilized chicken egg
9.12 Make a cardboard box incubator
9.13 Make a Styrofoam cool box incubator
9.14 Study the development of the chicken embryo
9.15 Measure the eggs
9.16 Make a warm brooder
9.17 Study the development of the hatched chickens
9.18 Find the sex of the chickens
6.3 Chicken life cycle (Primary)
Chicken Project

9.1.3 Sea animals and fish
5.1 Sea animals and plants (Primary)
5.2 Protect sea animals (Primary)
5.3 Corals and jellyfish - coelenterates (Primary)
5.4 Shellfish - molluscs (Primary)
5.5 Starfish, echinoderms (Primary)
5.6 Fish life cycle (Primary)
4.3 Parts of a fish (Primary)
5.7 Food chains in the sea (Primary)

9.1.4 Insects
9.19 Insect collecting net, air net
9.20 Insect collecting net, sweep net
9.21 Insect-killing container
9.22 Insect stretching board
9.23 Mounting boxes for insect collections
9.24 Make a mounting block guide
9.25 Make a simple insect cage
9.26 Make an insectarium
9.27 Keep a diary of insect behaviour
9.28 Collect night insects
9.29 Insect collector
9.7 Butterfly life cycle
9.8 Mosquito life cycle, Culex
9.9 Body of cockroach or grasshopper
9.34 Ant study
9.35 Cultures of fruit flies
9.1.7 Honeybee body structure, Apis mellifera

9.1.5 Earthworms and flatworms
9.33 Earthworm behaviour, Lumbricus
9.36 Flatworm behaviour, Dugesia, Planaria

9.1.6 Amphibians and reptiles
4.4 Frog life cycle (Primary)
4.5 Lizards and snakes (Primary)
6.2 Protect our turtles (Primary)

9.1.7 Mammals
9.30 Simple animal traps
9.31 Cages
9.32 Food and water
4.6 Care of dogs (Primary)
3.6 Care of cats (Primary)
6.4 Pig life cycle (Primary)
Cattle Project
Goat Project
Pig Project

9.2.0 Populations
9.204 Yeast population, bakers' yeast Saccharomyces cerevisiae, Phylum Ascomycota
9.205 Sampling yeast populations
9.206 Find wild yeasts in flowers
9.29 Human population growth

9.3.0 Communities and ecosystems
9.34 Establish an artificial community of aquatic organisms
9.35 Succession in a pond community, hay infusion cultures
9.36 Rotting log community
9.37 Desert community
9.38 Meadow community
9.39 Forest floor community
9.40 Pond ecosystem
6.1 Food chains in the forest (Primary)
3.32 Soil animals (Primary)
5.32 Protect our mangroves (Primary)
6.29 Protect our coral reefs (Primary)

9.4.0 Chromosomes and DNA
9.4.1 Root tip of onion cells showing mitosis
9.4.2 DNA and RNA
4.4.1 Isolate DNA

9.6.0 Drosophila experiments, Mendel's laws
9.6.1 Cultures of fruit fly (Drosophila melanogaster), for heredity experiments
9.6.2 Fruit fly strains
9.6.3 Mendel's experiments
9.6.4.1 Mendel's first law, law of uniformity (inheritance of one pair of characteristics)
9.6.4.2 Mendel's first law, law of uniformity (inheritance of two pairs of characteristics)
9.6.5 Mendel's second law, law of segregation
9.6.6 Mendel's third law, law of independent assortment
9.6.7 Sex-linked inheritance, introduction of recessive characteristic by female
9.6.8 Sex-linked inheritance, introduction of recessive characteristic by male
9.6.9 Genetics, lethal factors
9.6.10 Giant chromosomes

9.1.0 Levels of organization
Life can be understood as a natural order of living things, groups of living things, and parts of living things. Organisms are individual life forms, e.g. a dog, tree, fish, earthworm, mushroom, or yeast cell. At both the upper level of organization, the biosphere, and the lower level, the possibility of another level of organization is uncertain. Students will study life most frequently at the central levels of organization, near the level occupied by organisms.
Conceptual scheme:
Group of organisms:
1. Biosphere
2. Biome
9. Community
4. Population
5. Organism
6. Organelle
Parts of organisms
7. Macromolecule, e.g. chlorophyll
8. Molecule
9. Atom
10. Atomic particle
Higher levels of organization
1. Population: A group of organisms comprising all of a particular kind is called a population. A sub population refers to the space that it occupies. For example, one may refer to the snail population in a classroom aquarium, or the population of that kind of snail in a pond. If no space is mentioned, it is assumed that the population consists of all snails of that type in the world.
2. Community: Populations do not exist in isolation. They are commonly found in an environment that they share with other populations. All the populations within a defined space form a community. A lake community consists of all the plant and animal populations found in the lake. The populations found in school grounds would be a community.
9. Biome: Certain large areas of the earth contain communities that are similar. This collection of similar communities is called a biome. A biome may occupy a large portion of a continent. For example, a grassland biome is found in the central portion of North America or inland Australia. Climate and topography are uniform across a biome.
4. Biosphere: Life on the earth is normally found within a few metres of the surface. This hollow spherical space is the biosphere. It contains all life on the planet.
Lower levels of organization
5. Organ systems: Animal organisms contain systems of organs that do vital functions, e.g. the circulatory system.
6. Organ: Most plants and animals contain basic structures called organs that in turn are composed of tissues, e.g. heart, leaf, lung, root. Simple plants and animals may not have distinct organ systems.
7. Tissue: A tissue is a group of similar cells that do a single function, e.g. muscle tissues are composed of cells that can contract and produce the "pull" of the muscle. Some organisms are composed of tissues, but do not have organs.
8. Cell: Tissues consist of individual units called cells. The cell is the fundamental unit in most organisms. Cells vary considerably in size from the largest, an ostrich egg, to one of the smallest micro-organisms. Cells vary in their function and degree of specialization. Organisms composed of a single cell are called unicellular organisms.
9. Organelle: Cells contain parts called organelles that you can easily see with a light microscope, e.g. the nucleus. The electron microscope allows study of the structure of organelles.
10. Macromolecule: Organelles are composed of large molecules, macromolecules, e.g. proteins, lipids (fats and oils) and nucleic acids (DNA and RNA).
11. Molecule: Macromolecules are long chains of linked individual molecules. A molecule is the smallest possible piece of a substance that retains the properties of the substance. Molecules are composed of atoms joined or bonded together. An atom is the smallest part of an element.
12. Atomic particle: Atoms are composed of fundamental particles, e.g. protons, neutrons, and electrons. This is the present limit of understanding of organization at the lower level.

9.1.1 Kingdom Protista (Protoctista), heterotrophic protists, i.e. do not carry out photosynthesis
Protista includes eukaryotes (have a nucleus) that are not animals, fungi or plants. The group is not a "natural group" and the membership is constantly changing as more research is done. Other small phyla could be added to the list below.

9.1.2 Division Chromista - heterokonts, haptophytes, cryptomonad
9.1.3 Phylum Heterokontophyta
Class Bacillariophyceae, Diatomophyceae, diatoms, Arachnoidiscus ehrenbergi
Class Chrysophyceae, Chrysophyta golden algae golden-brown algae Ochromonas, Dinobryon, Chrysamoeba
Class Chytridiomycetes (Phylum Chytridiomycota), chytrids, Algae: Heterokontophyta zoosporic fungi, aquatic fungi
Class Dictyochophyceae, Actinochrysophyceae, Silicoflagellates, Dictyocha
Class Eustigmatophyceae, Nannochloropsis
Class Hyphochytridiomycetes (Phylum Hypochytridiomycota)
Class Phaeophyceae, phaeophyta, brown algae, rock weed, kelps Macrocystis, Sargassum
Class Raphidophyceae, red tides
Class Xanthophyceae yellow-green algae
Class Opalinea Opalina in frogs, Protoopalina
Class Oomycetes (Phylum Oomycota), water moulds, rusts, Phytophthora infestans causes potato blight, Phytophthora ramorum causes oak blight, downy mildews damage grapes, Pythium, Aaprolegnia, Achyla
9.1.4 Phylum Haptophyta, algal blooms
9.1.5 Phylum Cryptophyta, Class Cryptophyceae, Cryptomonas

9.1.6 Phylum Dinoflagellata, dinoflagellates, red tides
9.1.7 Phylum Apicomplexa, sporozoans, Babesia causes Babesiosis, Plasmodium causes Malaria, Cryptosporidium causes Cryptosporidiosis, Toxoplasma gondii causes Toxoplasmosis
9.1.8 Phylum Ciliophora, ciliates, Paramecium, Tetrahymena, Balantidium, Vorticella
9.1.9 Phylum Euglenozoa, (Phylum Sarcomastigophora), Euglenophyta, Euglenoidea, euglenoids, Euglena, Peranema, Phacus, Trachelomonas, Trypanosoma brucei causes African sleeping sickness, Trypanosoma cruzi causes Chagas disease in South America, Leishmania causes leishmaniasis, Giardia causes "traveller's diarrhoea"
9.1.10 Phylum Percolozoa Naegleria fowleri

9.1.11 Phylum Actinopoda, radiolarians, plankton, shells form geologic beds
9.1.12 Phylum Foraminifera, shell form limestone rocks, White cliffs of Dover, England
9.1.13 Phylum Cercozoa, amoeboids and flagellates, Euglypha, Trinema, cabbage club root fungus Plasmodiophora
9.1.14 Phylum Rhodophyta, red algae, used to make agar, dulse, nori, carrageenan, Gracilaria, Palmaria
9.1.15 Phylum Glaucophyta, Cyanophora, Glaucocystis
9.1.16 Phylum Amoebozoa Phylum Rhizopoda, Amoeba, Entamoeba histolytica causes amoebic dysentery (has no mitochondria)
9.1.17 Class Mycetozoa (Phylum Myxomycota), Myxomycetes (acellular or plasmodial or coenocytic slime moulds), unit is a plasmodium, Stemonitis, Physarum polycephalum
9.1.18 Phylum Choanozoa Proterospongia
9.1.19 Phylum Metamonada, have no mitochondria, Giardia lamblia causes "beaver fever", Trichomonas vaginalis causes trichomoniasis, Trimastix
9.1.20 Kingdom Discicristates, Phylum Acrasiomycota, Family Acrasiomycetes, (cellular slime moulds) cause powdery scab on potatoes

9.29 Human population growth
Compare the results obtained with yeast populations with a curve of human population growth. If a microscope is not available for yeast cell counting, compare daily counts of fruit flies or another available population that grows rapidly.
The birth rate, b - death rate, d = rate of natural increase, r. So if birth rate is 14 per 1000 per year and death rate is 8 per 1000 per year, the rate of natural increase is 6 per thousand, 0.6%. In February 2008, the total human population was estimated at almost 7 billion, 7,000,000,000. However, the rate of increase has declined since the 1963 peak of 2.2% per year.
In 1798, the Rev. T. R. Malthus (1766-1843) published a famous "Essay on population" which included the idea that population tends to outrun the means of subsistence. He advocated late marriage and sexual continence to control the increase of population. However, he may not have realized that the apparent increase in population was influenced by the decrease in death rate. Nowadays, an important factor in population growth is that people in developing countries are living longer.

9.34 Establish an artificial community of aquatic organisms
See diagram 9.37: Daphnia | See diagram 9.39.1d: Algae
1. Study communities. A grouping of populations in a particular location is called a community. Typically, communities consist of plants and animal populations that perform certain roles. Some populations are the producers. They are so called because they can trap energy from sunlight and producing food. Populations that feed on other living populations are called consumers. Those populations that feed on dead material are called reducers, since they disorganize organic matter to yield simpler chemical substances.
2. Establish natural communities. Use a closed plastic container or a fish tank with a glass lid so that only light can enter. Seal the lid with melted wax. Submerge the container in water to show that the system is not open to air. Try to create a balanced community so that the different kinds of organisms survive for a long time. Select a community to enclose, e.g. a square spade width of your garden or lawn, a forest floor community, ferns and liverworts, a dead animal, a rotting log, water from a pond.
3. Study living things both in the classroom or laboratory, especially aquatic plants and animals by making an aquarium for aquatic organisms. Make it ready in advance, so that you may put samples taken from a visit to a pond or stream in it upon our return.
4. Jam container aquarium: Use a large glass tank for a simple aquarium if it is well stocked with submerged water plants to aerate the water, e.g. Elodea or Myriophyllum. Use a jam container for keeping caddis larvae, pond snails, small crustaceans and plants. The pond life will remain balanced if carefully stocked. Feed Dytiscus beetles or other predacious larva on tadpoles and keep in a separate tank. Use 3 cm clean sand to provide hibernating quarters for the caddis flies at the bottom of the container, and attach a muslin cover to ensure that the caddis flies do not escape. Record egg laying, other changes, and habits. Use a strainer or net to collect aquatic specimens. Do not put an aquarium in direct sunlight because excessive light produces a heavy growth of algae on the glass walls that obscures the contents of the aquarium. Wipe off algae growths with an abrasive dish cloth.
5. Large aquarium: Find fine silt from the bottom of a clear stream or pond and wash it carefully in running water. Use it to cover the floor of the aquarium to a depth of 3 cm. Plant water plants and weigh down the roots with stones. Add coarse sand, gravel and stones for hiding places. To reduce cloudiness, fill with a slow stream of water falling on a sheet of cardboard and allow to stand for a day or two until clear. Then plant washed water plants. If many waterweeds are present aerating by pumps is not needed. Add live food, e.g. Daphnia, and snails to keep the glass clean. Very little feeding will be necessary. Fish will eat the snails' eggs and small water organisms introduced with the water plants. If worms are used as food, add them only once a week. Cut them in pieces small enough to eat. Remove food not consumed immediately or fungi will grow and infect the fish. Cover the aquarium with a glass plate to keep out dust. If frogs or newts are kept, put in a floating piece of cork to sit on.

9.35 Succession in a pond community, hay infusion cultures
See diagram 9.38: Amoeba, Paramecium, Euglena | Closed community
1. Put dry grass in boiled water in two sealed containers. Keep one container in the light and the other in the dark. Examine the container daily with the eye, with a magnifying glass and examine a water sample with a microscope. At first see bacteria, later ciliated protozoa and later rotifers, nematodes and crustaceans. Note the disappearance of populations and the appearance of new populations. Compare gross changes seen with the eye to the changes seen with the microscope.
2. Use the hanging drop technique. Dip the open end of a test-tube in petroleum jelly to make a ring on the centre of a microscope slide, slightly smaller than the size of a coverslip. Put the sample drop of water on the centre of the coverslip. Pick up the coverslip and invert it so that the drop hangs down. Lower the coverslip over the microscope slide so that the petroleum jelly supports the coverslip. Examine the contents of the hanging drop with low power.
3. To culture pond organisms, dissolve 1/2 teaspoon of bakers' yeast in 1 litre of boiling water and add some vegetable, e.g. peas. Inoculate the solution at room temperature and keep in indirect sunlight.
4. Combine or average the data derived from a ten day population growth study and graph the results for the entire class. (Remember that the two-day-old culture was started on the eighth day!). Compare the results obtained with yeast populations with a curve of human population growth. If a microscope is not available for yeast cell counting, compare daily counts of fruit flies or some other available population that grows rapidly.

9.36 Rotting log community
See diagram 9.36.2: Rotting log community
Break open a rotting log with a trowel, put two or three chunks into a plastic bag, and take them back to put in the terrarium. Construct a terrarium from an aquarium with a cloth cover. No soil is needed. If the log was in a damp place, add water to the terrarium from time to time. Many creatures may live in the log including ants, termites, spiders and horned beetles. If the log contains ants, provide a few crumbs and sugar water on a piece of sponge for them. To keep the ants from crawling out of the terrarium, spread a layer of Vaseline along the upper edge. Water to see what kinds of insects and other animals come from the log. Some may be eggs when you collect the log and may develop into adults while in the terrarium.

9.37 Desert community
See diagram 9.36.3: Desert community
Get sand from a beach or garden supply store. Some kinds of desert animals, including horned lizards, can be found in pet shops. The lizards will eat small insects, e.g. ants and meal worms, available from pet shops. Get small cacti and other succulents, which are plants that hold water in their fleshy leaves. Put rocks in the terrarium, making cliffs or overhangs near the edges. Put a small dish of water in one corner. Leave an open area of sand in the centre, especially if you have a horned lizard. Keep the temperature of the desert terrarium between 20oC and 27oC.
9.38 Meadow community
See diagram 9.36.4: Meadow community
Use only few of the grasses, weeds, seedling trees, and other plants that grow in meadows. Choose from the many animals. Orb spiders need lots of room to make their webs, e.g. a 50 litre aquarium tank. Find plants with insect eggs or cocoons on them and watch them to see what hatches. A small snake will eat earthworms and large insects but keep the terrarium dry because snakes often get skin diseases if kept in damp surroundings
9.39 Forest floor community
See diagram 9.36.5: Forest floor community
This is the kind of habitat most often modelled in a terrarium. For plants, obtain small ferns, tree seedlings, wildflowers, and especially evergreen plants, e.g. partridge berry or wintergreen. Put a few of these plants into the soil and cover the rest of the surface with mosses, attractive stones, and perhaps a small limb. For animals, look for small toads, frogs, e.g. cricket frogs or tree frogs, and red newts, small salamanders. These animals and the plants of the forest floor all need moisture, so keep the terrarium watered and make a small woodland pool in one corner.
9.40 Pond ecosystem
See diagram 9.36.0: Pond ecosystem
An ecosystem is the living community plus the non-living surroundings. An ecosystem is studied by observing and measuring relationships between its various subsystems. For example a pond community contains a great variety of plants (producers), animals (consumers), and decomposing micro-organisms (reducers). Observe the feeding habits and dissect organisms' stomach contents to understand the food chain in the ecosystem without destroying the ecosystem being studied. Beware of using inference instead of direct observations. The presence of a frog and a bee in the pond ecosystem may to the conclusion that a link on the food chain is bee to frog. However, the bee may not be eaten by frogs and would never appear in the frog stomach contents.

9.4.1 Root tip of onion cells showing mitosis
See diagram 9.107.1: Mitosis in onion root tip cells | See diagram 9.107.2: Cell division
1. The fundamental reproductive process called cell division may be studied by selecting an appropriate tissue that is growing rapidly. A good source of such cells is the root tip region of onions or other related plants. Onion bulbs, garlic cloves or onion sets placed in an aerated water bath provide large quantities of material. Cut off the white root tips of healthy specimens. Cut a 3 mm cylinder from the end of a root. Put it in a drop of aceto-carmine stain on a microscope slide. Cut up the onion tip with a razor blade until the pieces are extremely small. Cover the preparation with a cover glass. With a piece of folded paper towelling over your thumb for protection, gently squash the pieces of root tip by pressing on the coverslip with a rolling motion. Do not allow the cover glass to slide. Then examine the preparation with the low power of a microscope. Look for dark stained threadlike bodies. These are chromosomes or mitotic figures. Find the find various types or stages and count the number of various stages. From this information estimate the relative lengths of time that the various stages are present in a reproducing cell.
2. Plant an onion or shallot in moist absorbent paper in a warm place to obtain roots. Cut off 1 cm lengths from the ends of roots and fix them in a solution of 1 part glacial acetic acid to 3 parts 95% alcohol. Leave for 24 hours. Put a piece of root in a drop of aceto-carmine on a slide. Cut off 3 mm of the tip and discard the rest. Gently warm over a spirit lamp. Place a coverslip over the drop of stain and apply gentle pressure to separate the cells. These cells will show stages in mitosis.
9. Put onion root tips in 1 mL orcein in a watch glass. Heat over a spirit lamp for 1 minute or until the tips are soft. Scrape the tips over a microscope slide to make an even smear. Add drops of glycerine and a coverslip.
4. Examine a prepared slide showing cells in various stages of mitotic division, e.g. a stained longitudinal section through the root tip of the onion.

9.4.2 DNA and RNA
DNA is the master molecule that carries all of the inherited characteristics (genes) of an individual in the form of chromosomes. Each individual (such as a human) receives one haploid set of 23 chromosomes from their father's sperm and one haploid set of 23 chromosomes from their mother's egg. The two sets come together at conception when the diploid zygote (fertilized egg) is formed. Each eukaryotic chromosome (the chromosomes of algae, fungi, plants and animals) carries thousands of genes, about 100,000 functional genes per cell. A chromosome is analogous to a high capacity storage disk (DVD disk), while genes are analogous to files on this storage disk. If a chromosome could be completely unravelled, it would reveal a long, ladder-shaped DNA molecule that is coiled into helical spirals. At intervals along this double helix, the DNA ladder is wrapped around small beads of protein called nucleosomes. There are also extra chromosomal genes in the form of bacteria-like (prokaryotic) plasmids within cytoplasmic organelles called mitochondria and chloroplasts. The uprights of the DNA ladder are alternating 5-carbon sugars (deoxyribose) and phosphates. The rungs of the ladder are nitrogenous base pairs, purine bases adenine and guanine and pyrimidine bases cytosine and thymine with adenine always pairing with thymine and guanine always pairing with cytosine. DNA and RNA have nucleotide sub units consisting of a phosphate, a sugar and a base. Every base pair has four different arrangements: A-T, T-A, C-G and G-C that allows millions of different possible arrangements in a DNA molecule. Tiny amounts of DNA can be cloned into millions of copies with the PCR technique (Polymerase Chain Reaction) to give enough DNA to sequence gels into banding patterns to represent different base pair sequences and determine genetic "fingerprints" for crime identification or show relationships among plant and animal species. The results can be compared with gene sequences in gene bank databases.

9.6.1 Cultures of fruit fly (Drosophila melanogaster) for heredity experiments
See diagram 15.5.1: Drosophila experiments
1. Attract fruit flies by putting overripe fruit in an open container, e.g. a glass jar. After trapping the fruit flies, transfer them to small containers containing fruit chunks, e.g. banana. Put a slice of ripe fruit in the bottom of the container and make a paper funnel with a hole in the end to fit the mouth of the container. Put the container in the open air. When six or eight fruit flies have entered (including both males and females), remove the funnel and plug it loosely with cotton wool.  The females are larger, with a broader abdomen. The males are smaller and have a black-tipped abdomen. Soon eggs will be deposited, and in 2 or 3 days the larvae will hatch. Put a piece of paper in the container for the larvae to crawl on when they are ready to pupate. The adult insects will come from the pupae. Put newly-hatched fruit flies in another container to start a new generation. To study fruit fly cultures, cut a piece of graph paper and stand it upright in the container so that you can sample a large population in the bottle by counting the number of pupae on the grid. Make daily counts of the eggs, larvae, pupae and young adults of the population in a bottle. Draw a graph to show the increase in population with time. Maintain the culture for as long as the flies continue to survive.
2. Use conical flasks for breeding. Prepare the artificial diet the day before. Add 2 tablespoons beet juice syrup to 1 litre water. Heat the mixture and stir constantly. Add semolina until a thick paste forms. Prevent moulds forming by stirring in 1 spatula tip of nipagine per litre. Pour the mixture into clean breeding flasks to a depth of 2 cm. After cooling, add 5 drops of a viscous suspension of bakers' yeast in tap water. Close the breeding flasks with cotton wool plugs. Before the flies are inserted, absorb any liquid collected on the surface of the feeding mixture with strips of filter paper to prevent the flies sticking to the surface. Transfer the flies by tapping the breeding flask on the palm of the hand so that the flies fall to the bottom. Quickly remove the cotton wool plug and place a collecting tube with the same size neck as the breeding glass on top of it. By lightly tapping and shaking the flask, you can get the flies to enter the collecting tube. Separate the two flasks and seal with cotton wool plugs. Apply diethyl ether to the plug of the collecting tube so that the flies are anaesthetized within 20 seconds. Shake the flies out on a sheet of filter paper and separate the sexes. Use 8 females and 15 males for each fresh breeding batch. The males are smaller than the females and the shapes of the abdomens differ. The abdomen of the female is larger, more pointed and has 4 or 5 black transverse rings. The abdomen of the male is smaller, more rounded with a black tip and has only two transverse rings. The male has a row of bristles on the first foot section of each front leg. To prevent the fruit flies sticking to the feeding mixture, transfer them to the breeding flask in small cones made from filter paper. Make the cone by twisting a piece of filter paper about 5 cm square around the end of a pencil. If unfertilized females are required, remove all the fruit flies from a breeding container containing a lot of pupae on the point of hatching and after 6 hours collect the fruit flies which have hatched. Since the males are unable to copulate until 8 hours after hatching, the females among them cannot be fertilized. Larvae obtained in the following manner are most suitable for preparing giant chromosomes. Breeding colonies should not be overpopulated so remove adults from the breeding glass after they have deposited their eggs. When the larvae are half grown, add more drops of viscous yeast suspension to the container and remove the cultures to a cool place, 15o9. Take the fully grown larvae which have crept up the glass wall just before pupation for use as specimens.
3. Drosophila medium is an artificial diet consisting of 20 g of agar, 135 g of sugar, 38 g of yeast, 0.12 g of nipagine (10 g L- 1 nipagine in 70% ethanol) made up in 1 L of water and incubated at 20°C.
9.6.2 Fruit fly strains
Different varieties are called mutants because they have developed by mutation of genes. Describe the following strains: Normal wild, vestigial vg, ebony e, white w, and Curly Cy. Anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them with a 6 X magnifying glass or stereoscopic magnifier. Differentiate between the strains by means of their physical characteristics, e.g. colour of body and eyes. Compile a table of observations:
Strain characteristic Normal - wild type
+
vestigial
vg
ebony
e
white
w
Curly
Cy
Colour of body - - - - -
Colour of eyes - - - - -

9.6.3 Mendel's experiments
Gregor Mendel (1822-1884) used garden peas (Pisum sativum) for most of his experiments because they have constant different characters, flowers of hybrids can be protected from all other pollen and hybrids and offspring can produce viable seeds. The seven different characteristics of peas he selected were round or wrinkled ripe seeds, yellow or green endosperm, grey-brown or white seed coats, smooth or wrinkled seed pods, green or yellow unripe pods, axial flowers along the stems or terminal flowers at the end of stems, long stems (tall)  or short stems (short).  He always started the experiments with true breeding plants so that their offspring  would be identical to the parents and so any changes in the progeny must be due to cross breeding. In 1865 Mendel published his study of inheritance that includes three principles concerning the inheritance of traits when cross-breeding.
The principle of uniformity is that if two plants that differ in one trait are crossed the will be uniform in the chosen trait which will be either one of the parents' traits. So when parent 1 is crossed with parent 2,  all the individuals of the hybrid, the first filial generation (F1) will have the same characteristic for any pair of characteristics. A unit of heredity is now called a gene and the list of different genes is called the genotype. Pairs of genes occupying the same place on different chromosomes are called alleles, e.g. the genes for round or wrinkled ripe seeds are alleles. The expression of genes in an organism is called the phenotype.
If true breeding tall plants are crossed with true breeding short plants and tall is dominant and short is recessive, the offspring, the F1 generation, will all be tall. In the following chequerboard, the two possible gametes of the tall plants are shown horizontally and the two possible gametes of the tall plants are shown vertically.

gametes
 T
 T
 t
 Tt (tall)
Tt (tall)
 t
 Tt (tall)
Tt (tall)

When an individual of the F1 generation is crossed with another individual of the same F1 generation,  the resulting hybrids are members of the F2 generation. The principle of segregation is that the individuals of the F2 generation are not uniform. Hereditary traits occur in pairs, one of each pair being inherited from each parent. During meiosis when gametes are formed, each pair of alleles, e.g. tall seeds / short seeds in the parent cells segregate (separate) into different gametes. So any gamete carries either the tall seeds or short seeds gene but not both and not neither.
In the following chequerboard,  the gametes produced by the two parents, shown horizontally and vertically, are either tall or short. If tall is dominant and short is recessive, let T = tall and t = short. The genotype of the offspring can be  TT (tall), or  tT (tall), or Tt (tall), or tt (short), so the ratio of phenotypes is 3 tall plants to 1 short plant. This study of one allele is called a monohybrid cross

gametes
 T
 t
 T
 T T (tall)
t T (tall)
 t
 T t (tall)
t  t (short)
Similarly the allele round or wrinkled seeds, round is dominant and wrinkled is recessive. Let R = round and r - wrinkled. The result of the monohybrid cross would be a ratio of 3 (round) to 1 (wrinkled) seeds. The genotypes TT and tt are said to be homozygous. The genotype Tt (or tT) is said to be heterozygous.
The principle of independent assortment is that each trait is inherited independently of the other traits so  new combinations of traits can occur which were not existing before. The segregation of one pair of alleles is independent of of the segregation of any other pair of alleles. This principle is valid only for genes on different chromosomes.
For a dihybrid cross the offspring have 16 possible different genotypes and the ratio of phenotypes is 9 (tall round), 3 (tall wrinkled), 3 (short round), 1 (short wrinkled).
gametes
TR
Tr
tR
tr
TR
TRTR (tall round)
TrTR (tall round) tRTR (tall round) trTR (tall
 round)
Tr
TRTr (tall round) TrTr (tall wrinkled)
tRTr (tall round) trTr (tall wrinkled)
tR
TRtR (tall round) TrtR (tall
 round)
tRtR (short round)
trtR (short round)
tr
TRtr (tall round) Trtr (tall wrinkled) tRtr (short round) trtr (short wrinkled)
Later, geneticists interpreted Mendel's principles as "Mendel's three laws" while others referred to principle 2 and 3 as Mendel's first and second law. 
9.6.4.1 Mendel's first law, law of uniformity (inheritance of one pair of characteristics)
According to Mendel's first law when homozygous strains are crossed which differ by one or more characteristics, the offspring in the first filial generation (F1) will all have the same characteristics. This is called the law of uniformity. To investigate the validity of Mendel's first law, put 8 unfertilized female fruit flies, normal wild strain (+), and 15 males, ebony strain (e), in each of two breeding flasks containing Drosophila medium. Then do a reciprocal hybridization with 8 unfertilized females, ebony strain (e), and 5 males, normal wild strain (+), in each of two breeding flasks containing the Drosophila medium. Leave the four breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the body colour of the first filial generation (F1) offspring in the four breeding flasks. Count the numbers of each sex after anaesthetizing them with diethyl ether. Use a magnifying glass to distinguish between males and females. Compare the body colour of the first filial generation (F1) fruit flies with the body colour of the parents. Note the sex ratio. The parent fruit flies are homozygous for the characteristics under investigation. The genotypes are +/+ for fruit flies with normal body colour and e/e for fruit flies with dark body colour. So the germ cells are + or + and e or e. Insert all possible combinations of the genes in the chequerboard diagram below. Note whether the theoretical result agrees with the practical result of this experiment.
. (+) male (+) male
(e) female - -
(e) female - -
. (e) male (e) male
(+) female - -
(+) female - -

9.6.4.2 Mendel's first law, law of uniformity (inheritance of two pairs of characteristics)
Put 8 unfertilized female fruit flies, ebony strain (e), and 15 male fruit flies, vestigial strain (vg), in each of two breeding flasks containing the Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the body colour and wing shape of the first filial generation (F1) offspring in both breeding flasks. Anaesthetize the fruit flies with diethyl ether. Place them on a sheet of filter paper and examine them under a magnifying glass. Compare their appearance with the parents The parent fruit flies, which were crossbreeds, possessed the following observable characteristics:
- Body colour Wing shape
Male Normal wild (+) Stump-winged, vestigial (vg)
Female Dark, ebony (e) Normal -wild (+)
The genotypes are the following: male vg / vg // + / +, female, + / + // e / e. To find what types of germ cells can be formed, insert all possible combinations of the genes in the chequerboard. Note whether the theoretical results agree with the experimental results. Draw a chequerboard and predict whether the result of the experiment would have been the same if both recessive characteristics were introduced by one parent in the hybridization.
- male (+) male (vg)
female (e) (+) (e) (vg) (e)
female (+) (+) (+) (vg) (+)

9.6.5 Mendel's second law, law of segregation
According to Mendel's second law, the characteristics of the parent generation recur in the second filial generation (F2) in a quite specific numerical ratio. Investigate the segregation of the dominant recessive characteristic pair normal wild/ebony (+/e) of the fly in the second filial generation. Put 8 female and 5 male fruit flies from one of the first filial generations (F1) from the previous experiment in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the body colour of the second filial generation (F2) offspring. Anaesthetize the fruit flies with diethyl ether and place them on a sheet of filter paper. Note the numerical ratio of the body colours of the parent fruit flies, Normal wild (+) and ebony (e). The genotype of the fruit flies of the first filial generation (F1) crossed in this experiment is +/e. The germ cells they can form are (+) or (e). Insert all possible combinations of the genes in a checker-board. Does the theoretical result obtained with the checker-board agree with the practical result from the hybridization experiment? Make a comparative table using both sets of results. Calculated numerical values from the checker-board and the numbers obtained by counting in the experiment. Note the deviations. Note whether all fruit flies having the same appearance have the same genetic constitution, i.e. do fruit flies with the same phenotype always have the same genotype.
. male male
female - -
female - -

9.6.6 Mendel's third law, law of independent assortment
According to Mendel's second Law the characteristics of the parent generation recur in an exact numerical ratio (subdivision ratio) In the second filial generation (F2), following the Law of Segregation. If different pairs of characteristics (alleles) are not contained on the same chromosome, they are distributed (assorted) independently during the formation of the germ cells and freely recombine. This process is called Mendel's third Law - the Law of Independent Assortment. Investigate the free recombination of genes, Mendel's third Law, in the fruit fly. Place 8 female and 15 male fruit flies from the first filial (F1) generation of the previous experiment in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. About 10 days after the first fruit flies have hatched, examine the offspring in both breeding flasks, the second filial generation (F2), for their body colour and wing shape. For this purpose, anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them under a magnifying glass. Note the number of different characteristic types, phenotypes. Count each of the different types. Note what phenotype has occurred for the first time. In the previous experiment, you crossed stump winged (vestigial, vg) and dark bodied (ebony, e) fruit flies of the parent generation. Their genotypes were vg/vs and +/+ respectively. +/+ e/e The offspring, in accordance with their genotypes +/vg, are normal coloured and have normal shaped wings. e/+. These fruit flies were crossed in the present experiment. Note what type of germ cells they can they. Insert all possible combinations of the genes in a checker-board. Determine the external characteristics of the fruit flies according to their respective genes. Note which characteristic types (phenotypes) must occur and how often. Note whether this theoretical result agrees with the practical result of the experiment.
. male male male male
female - - - -
female - - - -
female - - - -
female - - - -

9.6.7 Sex-linked inheritance, introduction of a recessive characteristic by female
The female has the pair of chromosomes (X/X) but he male has the genotype (X/Y) so the genes on the X chromosome are distributed differently in hybridization from those on the other chromosomes.
Investigate the inheritance of the sex-linked recessive characteristic white (white-eyed, w) in the fly introduced by the female in hybridization. Put 8 unfertilized female fruit flies, white strain (w), and 15 male, Normal-wild strain (+) in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the eye colour and sex of the first filial generation (F1) offspring in both breeding flasks. Anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them under a magnifying glass. Record the results in a table as follows:
- male female
White eyes - -
Normal-coloured
(red) eyes
- -
Note whether the result in accordance with Mendel's first Law. The gene for eye colour is on the X chromosome. The females have two X chromosomes. In this experiment they are white-eyed and their genotype is w/w. The males possess only one X chromosome. In this experiment they have normal coloured (red) eyes and their genotype is +/y. Note what type of germ cells can be formed and insert all possible combinations of the genes in a checker-board that follows. Determine the external characteristics and sex of the files according to their respective genes. Note whether this theoretical result agrees with the result of the experiment.
- male male
female - -
female - -
2. Put 8 females and 5 males of the first filial generation (F1) from the above experiment in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the eye colour and sex of the second filial generation (F2) offspring in both breeding vessels. Anaesthetize the fruit flies with diethyl ether, place them on a sheet of filter paper and examine them under a magnifying glass. Count the files and record the results in the following table:.
. male female
white eyes - -
normal coloured (red) eyes - -
Note the genotype of both the males and females of the first filial generation. Note the types of germ cells they can be formed. Insert all possible combinations of genes in the checker-board that follows.
Determine the external characteristics, phenotypes and sex of the fruit flies according to their respective genes. Note whether the theoretical results agree with the practical result of the experiment.
. male male
female - -
female - -

9.6.8 Sex-linked inheritance, introduction of a recessive characteristic by a male
1. In the preceding experiments you investigated the heredity process when a sex-linked recessive characteristic is introduced by the female during hybridization. Investigate the heredity mechanism when this characteristic is introduced by the male when the sex-linked recessive characteristic white (white eyes, w) in the fly is introduced by the male. Put 8 unfertilized female fruit flies, Normal-wild strain (+) and 15 males, white strain (w) in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the colour of the eyes of the first filial generation (F1) offspring in both breeding flasks. Anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them under a magnifying glass. Note whether the result is in accordance with Mendel's first Law. Note the genotypes of the parent fruit flies and the germ cells can they form. Insert all possible combinations of the genes in the following chequerboard.
Determine the external characteristics, phenotypes, of the fruit flies according to their respective genes. Note whether the theoretical result obtained with the chequerboard agrees with the practical result of the experiment.
. male male
female - -
female - -
2. Put 8 females and 15 males of the first filial generation (F1) from the above experiment in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the eye colour and sex of the second filial generation (F2) offspring in both breeding flasks. Anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them under a magnifying glass. Count the fruit flies and record the results in the following table.
. male female
white eyes - -
normal coloured (red) eyes - -
Note the ratio of red-eyed to white-eyed fruit flies. Note how the eye colour is distributed between the sexes and the genotype of the fruit flies of the first filial generation. Note what types of germ cells these fruit flies can form. Insert all possible combinations of the genes in the following chequerboard. Determine the external characteristics (phenotypes) and sex of the fruit flies according to their respective genes. Note whether this theoretical result agrees with the practical result of the hybridization experiment.
. male male
female - -
female - -

9.6.9 Genetics, lethal factors
After many mutations, the genotype may become altered to such an extent that the offspring are no longer viable. Genes that mutate in this way are called lethal factors, e.g. (CY) mutant of the fruit fly. These fruit flies have upwards curving wings. The characteristic is dominant. Fertilized egg cells in which (CY) it is homozygous do not develop. Put 8 unfertilized female and 15 male fruit flies, curly strain (Cy), in each of two breeding flasks containing Drosophila medium. Leave the breeding flasks to stand at room temperature. Ten days after the first fruit flies have hatched, note the shape of the wings of the offspring in each breeding container. Anaesthetize the fruit flies with diethyl ether. Put them on a sheet of filter paper and examine them under a magnifying glass. Count the fruit flies with upwards curving wings and normal wings. The dominant characteristic Curly homozygous fruit flies, genotype (CYCY), cannot exist so the hybrid fruit flies must have the genotype Cy/+. Insert all possible combinations of the genes in the chequerboard. Determine from the checker-board what ratio there ought to be of fruit flies with upwards curving to normal wings in the first filial generation (F1). Note whether this theoretical value corresponds to the practical result of the experiment. Note the apparent deviation from Mendel's Laws and why it occurs.
. male male
female - -
female - -

9.6.10 Giant chromosomes
Investigate the form and structure of the giant chromosomes in the salivary gland cells of the larva of the fruit fly. Press carefully on the coverslip with the handle stem of a dissecting needle until the salivary glands disintegrate into individual cells. Apply slightly more pressure to squash the cells so that the chromosomes are pressed out. Use filter paper to draw off the acetic acid which has spread under the coverslip and examine the preparation under a microscope with preferably an oil immersion lens, magnification not less than 40 x. Put a larva of the fly in a large drop of carmine acetic acid on a microscope slide. Hold down the larva by pressing the side of a dissecting needle horizontally across it, about one third of the way along from the end of the abdomen. Pierce the exoskeleton by pressing the point of another dissecting needle at a slight angle from the horizontal into the larva between the second and third segment, i.e. directly behind the fauces. Pull the head section of the larva forwards until it becomes detached from the rest of the body, pulling the organs attached to it out of the body. Identify the salivary glands from by their club-like shape and glazed appearance. Remove the attached fatty tissue. Transfer the salivary glands to a fresh drop of carmine acetic acid on a second slide and place a coverslip over them. After 2 minutes place a drop of 45% acetic acid on the edge of the coverslip and draw it across under the coverslip by placing the edge of a filter paper strip at the opposite edge of the glass. The chromosomes in the salivary gland cells of the larvae of fruit flies are so large they are called giant chromosomes. These chromosomes form by repeated longitudinal division of the chromatic thread without subsequent splitting of the products of the division. Note their shape and structure.