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.