BC2003: LAB 5
REPRODUCTIVE STRATEGY IN EUKARYOTES
OCTOBER 11-15, 2004
Questions to think about:

What microscopic or macroscopic characters unite the Kingdoms Animalia, Planta, Fungi and
Protista? How does this relate to the name of the Domain Eukarya?

What are the pros and cons of sexual reproduction? Do they depend on the environment?
What evidence can you use to support your arguments?

What are the pros and cons of producing two types of gametes? Or two types of individuals,
each specialized to produce just one type of gamete? What types of organisms have these
forms of specializations? Have such specializations have evolved just a single time, or
multiple times in different branches of the overall family tree of life?

Can you think of any advantage to the production of dikaryotic cells in fungi? Did this type
of life cycle evolved just once, or independently in the different divisions within Kingdom
Fungi?

What is the biological definition of sex?
Learning objectives:
1.
Understand how and why biologists recognize and describe the Domain Eukarya.
2.
Compare and contrast asexual and sexual reproduction, including the advantages and
disadvantages of both.
3.
Understand that eukaryotic life cycles alternate between haploid and diploid phases.
4.
Understand the meaning of the terms zygote and gamete.
5.
Describe examples of hermaphroditism, as well as separate male and female sexes.
6.
Understand the terms isogamy and oogamy and recognize examples of each from the algae (in the
Kingdom Protista)
7.
Using members of the Division Ascomycota in the Kingdom Fungi as an example, describe
karyogamy, plasmogamy, and the dikaryotic condition.
Reading in Campbell Biology textbook:
Ch. 13: Figures 13.4 and 13.5abc.
Ch. 28: Read chapter, study pp. 565-567 and Figure 28.24.
Ch. 31: Read chapter, study Figures 31.3, 31.7, 31.10.
fall 2004, Lab 5-1
LAB OVERVIEW
Well-educated biologists are familiar with the enormous diversity in how sexual reproduction occurs. You
probably started the course quite familiar with the human life cycle, which is fairly typical of vertebrates.
Today we will briefly re-visit sex in animals, but we will emphasize organisms found in the Kingdoms
Protista and Fungi. Next week, you will study plants and their life cycles.
 Prepare for today’s quiz by reading this handout.
 Attend recitation lecture and review your notes before lab.
BEFORE CLASS
 In your textbook:
 Study the generalized life cycle diagrams in Figures
13.4 and 13.5. Review differences between mitosis
and meiosis as detailed in Figure 31.5.
 Read about green algae on pp. 565-567, especially
the life cycle diagram in Figure 28.24.
 Also study the diagrams of fungal life cycles in Ch.
31, Figures 31.3, 31.7, 31.10)
 Examine all fresh specimens and prepared slides.
DURING CLASS, IN PAIRS
 When making observations, relate the organisms and the
structures with the corresponding phases in a life cycle.
ASSIGNMENT
Complete the worksheets and turn them in at the beginning of
lab next week.
PREPARE FOR
LAB PRACTICAL EXAM
The lab practical exam will take place in the first hour of next
week’s lab. Be prepared to identify structures, describe
functions, and answer questions based on recitation material,
your labs and their analyses, lab handouts, and textbook reading.
fall 2004, Lab 5-2
INTRODUCTION
The Domain of Sex
For most of this semester, we emphasize the Domain Eukarya, one of the three domains used to classify
all living organisms. The other two domains, Domain Bacteria and Domain Archaea, are prokaryotic.
Eukaryotic cells differ from prokaryote cells in having a nucleus bound by a nuclear membrane and other
membrane-bound organelles such as mitochondria, endoplasmic reticulum, and the Golgi body.
Today in lab, we will emphasize eukaryotic organisms found in the Fungi and Protista Kingdoms.
Kingdom Protista is a paraphyletic or polyphyletic group that some believe should be divided into several
monoplyletic kingdoms, each reflecting a single evolutionary lineage. Historically, the term “Protist”
referred to all single-celled organisms; some scientists use the term “Protoctista” to refer to the Protista
kingdom in order to avoid confusion. In this course, we will treat all protists/protoctists — the protozoans
and the algae — as a single kingdom called “Protista” or “Protoctista.”
Although eukaryotic organisms in various kingdoms are capable of asexual reproduction, sexual
reproduction is also an important characteristic in most eukaryotic organisms. It is important for you to
understand how sexual reproduction relates to the ability of eukaryotic cells to undergo meiosis.
Today we will examine how meiosis and fertilization – the essences of sex – occur in the life cycles of
several algal and fungal examples. Next week we will study plant life cycles and further examine how
sexual reproduction involves meiosis and fertilization.
The Essence of Sex
In eukaryotes, the genetic material is arranged in sets of chromosomes surrounded by a nuclear
envelope or nuclear membrane. Cells that contain a one copy of each chromosome (one set) in their
nuclei are said to be haploid, as in gametes (e.g. egg and sperm) and plant spores and gametophytes.
Cells that contain two copies of each chromosome (two sets) in their nuclei are said to be diploid, as is
true of the non-reproductive tissues of animals and higher plant sporophytes. Note that there are many
polyploid organisms whose nuclei contain more than two sets of chromosomes; polyploidy is particularly
common within the plant kingdom. Through mitosis and cytokinesis, the cells of haploid, diploid, or
polyploid organisms can divide, permitting asexual reproduction or various forms of multicellularity.
Remember that mitosis is a form of karyokinsis (nuclear division) that results in the production of two
nuclei that are genetically identical to each other and to the mother nucleus. It is often accompanied by
division of the cell itself, cytokinesis.
Meiosis, a process that complements fertilization in sexual reproduction, reduces the number of copies of
each chromosome in half. As such, haploid cells are unable to divide by meiosis, because they only
contain one copy of each chromosome. When a diploid nucleus divides by mitosis, two genetically
identical diploid nuclei are formed. When this same diploid nucleus divides by meiosis, four genetically
distinct haploid nuclei are formed. The meiotic daughter cells do not receive an intact copy of any of the
chromosomes present in the mother cells; during the beginning stages of meiosis, crossing-over (or
recombination) occurs, mixing the genetic information among the copies of the same chromosome. In
fertilization, haploid nuclei of specialized single-celled gametes fuse. The resulting diploid cell is known
as a zygote. Note that meiosis can occur in polyploid organisms having an even number of copies of each
chromosome; a plant cell with 8 copies of each chromosome can divide by meiosis to form 4 cells that
each contains 4 copies of each chromosome. Meiosis cannot occur in a polyploid organism with an
uneven number of chromosome copies; such organisms are sterile and must reproduce by asexual means.
fall 2004, Lab 5-3
“Triploidy may be rare in wild plants; however, it is a favored condition in many economically important plants.
Plant breeders have learned that triploidy can produce economically valuable traits in crops and ornamental plants.
The only drawback is that the plants cannot be perpetuated by the seeds of the triploid plant. Triploidy prevents
normal homologous chromosome separation, leaving the plants with abnormal seeds that rarely develop. Thus, the
plants must be propagated regularly by cross-breeding or vegetative means such as cuttings.
Seedless plants are the major benefit of triploid plants. Watermelons are commonly raised triploid to avoid
undesirable seeds that affect the fruit's edibility. Each season, fresh triploid seeds are sold to farmers because these
watermelons cannot be propagated naturally. Seeds that produce seedless watermelons are difficult to germinate
and require more exacting conditions to grow than standard diploid watermelon varieties. Currently, the seeds cost
six to 60 times more than seeded watermelons, thereby making them too expensive for many small farmers and
developing nations.
Grapes, mustards, oranges, radishes and many ornamental plants are sold as triploids. The crops are valued for
their seedless properties, and their triploid condition can also result in extra pulp production. Ornamental flowers
sometimes take on a larger size and brighter colors when bred triploid. In addition, the seeds cannot be taken from
the cut flowers and grown illegally.” (from: http://wps.prenhall.com/esm_graham_plantbio_1/0%2C6615%2C395706-%2C00.html)
The double set of chromosomes in a diploid cell represents the combined contribution of a single set of
chromosomes from each parent. The chromosome number is often expressed in shorthand notation, n or
1n for the haploid number and 2n for the diploid number (for a polyploid organism, notations such as 6n,
12n, or 3n would be used). These notations are used extensively on diagrams of life cycles.
Three basic types of life cycles occur in eukaryotes, based on the timing of meiosis:
1. In a life cycle with gametic meiosis the only haploid cells are the gametes, and the organism you
are most likely to observe is diploid because that phase is longer in duration and larger in size.
This is the pattern in most animals. (see Fig. 13.5a, page 238 in Campbell 6th edition) Meiosis
typically occurs in specialized tissues that produce gametes, and when the gametes fuse in
fertilization the diploid condition is immediately restored.
2. In a life cycle with zygotic meiosis the only stage that is diploid is the zygote, and meiosis occurs
in that single-celled stage of the organism. As a result, most of the life cycle, and the stage of
organism you are most likely to see, is haploid. Gametes, the cells that will participate in
fertilization, may be produced in specialized structures, but this involves mitosis, not meiosis,
since the entire organism is already haploid. This life cycle is typical of many members of the
Kingdoms Protista and Fungi (see Fig. 13.5b, page 238 in Campbell 6th edition). However, there
is a distinctive twist — the formation of dikaryotic cells — that occurs in some fungal life cycles
you will examine carefully today.
3. In plants and in many macroscopic, photosynthetic protists (algae commonly referred to as
“seaweeds”) there is alternation between the haploid and the diploid condition, and both stages
are multicellular (see Fig 13.5c, page 238 in Campbell 6th edition). These organisms have a life
cycle with sporic meiosis since the diploid stage produces haploid spores by meiosis, often in
specialized structures. However, these haploid cells are not gametes and do not participate in
fertilization. Rather, they germinate and form a completely haploid multicellular, independent
organism. This haploid stage in turn produces the gametes that fuse to form a zygote. The zygote
develops into the diploid stage once again. The diploid stage, because it produces haploid spores,
is called the sporophyte. The haploid stage of the life cycle, because it produces gametes, is
called the gametophyte. The cycling between the two stages is referred to as alternation of
generations. Alternation of generations is also found in the plant kingdom, which we will
examine in greater detail next week.
fall 2004, Lab 5-4
Variations on gametic meiosis
Many animals have this form of sexual reproduction. In humans, as in almost all vertebrates, males
produce only sperm and females produce only eggs. The situation in the fetal pig is extremely similar,
and you may want to review the photographs of the various sexual organs in your photographic atlas of
the fetal pig. Crayfish also have separate sexes, and you should remember how it is possible to tell male
from female in the crayfish.
In such animals, copulation behaviors aid in the transfer of sperm to eggs. Fertilized eggs — zygotes —
have various fates depending upon the organism. In hermaphroditic species, every individual can
function as both an egg-producing female and a sperm-producing male. Typically, however, crossfertilization between different individuals is the rule. Earthworms, in the Phylum Annelida, are a good
example of this condition.
A. The simple life cycle of Chlamydomonas (Kingdom
Protista/Protoctista)
A variation on zygotic meiosis:
The unicellular photosynthetic alga protist
Chlamydomonas has a basic, zygotic type of life cycle.
Only the zygote is diploid (2n), and all other cells are
haploid (1n). As indicated in the diagram, an individual
cell can itself act as a gamete and fuse with another cell
of the opposite mating strain.
To a certain extent, this organism seems to ‘lack sex.’
There is no visible distinction between the two gametes,
i.e. one is not an egg and the other a sperm. This is a
condition known as isogamy (from the Greek meaning
‘similar mates’). Be sure that you can describe the
difference between isogamy and hermaproditism.
Fusion by the haploid cells forms a zygote, which
develops a thick wall that allows it to survive adverse
conditions. When conditions are suitable for growth, the
zygote undergoes meiosis and releases new haploid,
photosynthetic cells.
DO ONLY THIS CHLAMY MATING STUDY IN GROUPS OF TWO; do the rest of the lab
individually. (Italicized print means in the lab handout indicates something you need to do.)
Start
this
early in
lab
You should watch the first stages of sexual reproduction in Chlamydomonas, mating and
fusion, as they happen. Chlamydomonas has two different matting strains (+ and -). Cells
can only participate in sexual reproduction if they are of different mating strains (+ cells
cannot mate with other + cells, nor can – cells mate with – cells).
We have three culture flasks of Chlamydomonas, labeled A, B, and C. Your task is to
determine which of the two cultures contain the same mating strain and which
contains the different mating strain.
fall 2004, Lab 5-5
Take a small drop from each of two culture flasks, and put the drops next to each other on a slide. You’ll
want to test A+B, B+C, and A+C (each pair on a different microscope slide). ****Be careful not to
cross-contaminate the flasks; sample each one only with its designated pipette.*** Mix the drops with a
clean toothpick, add a cover slip (being careful not to get air bubbles underneath), and observe under the
high power (40X objective)of your compound scope.
Mating and fusion are a gradual process, requiring about an hour, so you should check your slides
periodically as you work through the rest of the lab procedures. The slides will start to dry out over time,
so be sure to add a little water to the edge of the cover slips occasionally. Turn the microscope light off
between viewings to slow evaporation.
Make several sketches of the isogamous gametes of Chlamydomonas on Worksheet One, record your
observations of mating, and compare the isogamous gametes to the oogamous gametes in Oedogonium.
In addition, draw conclusions about which of the three cultures contains a mating strain different from
the other two.
B. Oogamy in Oedogonium (Kingdom Protista/Protoctista)
A variation on zygotic meiosis:
Not all green algae are isogamous. Oedogonium is a simple unbranched filamentous alga with a division
of labor between vegetative and reproductive cells. It is an example of oogamy, which differs from
isogamy in having distinct female and male gametes. A small flagellated sperm fertilizes a large
nonmotile egg. There is thus a distinct division of labor, or specialization, between vegetative and
reproductive cells.
Make a wet mount of living Oedogonium filaments and observe under the microscope. You may also
wish to look at the preserved demonstration slides of the reproductive structures. On Worksheet One,
draw some representative strands of Oedogonium, including reproductive structures.
Sexual reproduction occurs after the development of specialized reproductive cells, antheridia and
oogonia. The antheridia are short disc-shaped cells that give rise to two male gametes. Does this
process involve mitosis or meiosis? The sperm produced by the antheridia have a ring of flagella at one
end and are released into the water in which the algae are living. The oogonia are large spherical cells
formed by differentiation of a single cell; they are not motile.
As the egg matures, a small opening develops in its wall through which the male gamete can enter. A
diploid zygote is formed by the fusion of the two different types of gametes, the egg and sperm. The
zygote develops a thick wall and is dormant. When environmental conditions are favorable, the zygote
will undergo meiosis and the four cells formed will develop into new haploid filaments.
fall 2004, Lab 5-6
You can pick up this figure in lab.
fall 2004, Lab 5-7
C. Sexual reproduction in the Division Zygomycota (Kingdom Fungi)
A variation on zygotic meiosis:
Many fungal organisms have a form of zygotic meiosis in which there is also a ‘lack of sex’ or, more
correctly, a lack of specialization for sex. As in Chlamydomonas, the gametes are alike morphologically,
but have genetic factors require a complementary mating strain in order for fertilization to occur. A major
difference is that free-living gametes are not formed; the cells that are specialized for sex remain attached
to the rest of the fungal organism (specifically, part of the mycelium; see definitions below).
A good example of this form of sexual reproduction occurs in the black bread mold, Rhizopus (you may
be familiar with this mold that is often found growing on strawberries and raspberries). This organism is
classified in the Division Zygomycota (Kingdom Fungi). It can reproduce sexually if two compatible
strains, “+” and “–” come in contact with one another. To understand how this works, it is necessary to
understand a bit about fungi in general, including the following specialized vocabulary:
Thallus: The entire body (mass) of an individual fungus, including the vegetative part, the
mycelium, and the reproductive parts.
Hypha: (plural, hyphae) A branching, threadlike tubule usually microscopic in size. When
clustering in huge masses, hyphae comprise the mycelium (see below).
Mycelium: (plural, mycelia) Vegetative, or food-assimilating, part of the thallus. Composed of
a mass of countless intermingled tubules called hyphae (see above). The mycelium typically
lives for several years and often isn’t seen because it grows under the soil surface or inside the
host material. Its general appearance is that of a white crumbly thready material.
Examine live specimens of Rhizopus in order to understand how these terms are applied. Please do not
open the dishes containing Rhizopus!!! Examine them through the transparent Petri dish cover
(we do not want every organism we study for the rest of the semester to be contaminated with
Rhizopus spores).
In Rhizopus, when two compatible mating strains come in contact, gametangia form at the tips of the
hyphae. Free, single-celled gametes are not produced. (See diagram on Worksheet Two.) Instead, as the
hyphae grow, the two gametangia touch and the cell walls join and the cell contents mix—through the
process of plasmogamy. Initially, the multiple haploid nuclei do not fuse; nor do they divide. This
single cell is, for a time, heterokaryotic (containing multiple unfused, genetically distinct nuclei).
(Compare this single-celled dikaryotic stage with the multi-cellular dikaryotic mycelium in the Division
Ascomycota; see below).
Eventually, the two nuclei do fuse to form a zygote and the entire structure develops a thick wall to
become the zygosporangium. When the zygosporangium germinates the zygote undergoes meiosis and
produces the haploid spores that give rise to new haploid hyphae.
Using a dissecting microscope and live specimens of Rhizopus, you should be able to make sketches in
the appropriate box of the life cycle diagram on Worksheet Two. Again, please do not open the dishes
containing Rhizopus. You can also examine prepared slides of Rhizopus, particularly to see the details of
the zygosporangia and sporangia.
Members of the Division Zygomycota, including Rhizopus, can also reproduce asexually. This occurs by
means of haploid spores produced in a bulbous or elongated sporangium borne on a stalk, the
sporangiophore.
fall 2004, Lab 5-8
Identify these structures in a colony of Rhizopus under your dissecting microscope. What gives the colony
the color noted in the common name?
Sketch and label a bit of hyphae with sporangiophores and sporangia in the appropriate box in the lifecycle diagram on Worksheet Two.
Both the zygosporangia and sporangia produce haploid spores, but how do they differ in function, i.e.,
what different purposes do they serve in the life cycle?
D. Division Ascomycota (Kingdom Fungi)
Zygotic meiosis and the dikaryotic condition:
The ascomycetes are a diverse division with a number of ecologically and economically important
species, including common blue and green molds, yeasts (found in beer, wine, and bread), and the
gastronomically prized morels and truffles.
Members of this division are characterized by their sac-like sexual reproductive structure called an ascus
(plural asci). An immature ascus contains the only truly diploid cell in the life cycle, the zygote. These
immediately undergo meiosis to produce haploid ascospores that are discharged when the asci mature.
(See diagram on Worksheet Two.) What kind of life cycle does this represent?
In most ascomycetes, the asci are borne on or within a dense mass of hyphae known as an ascocarp. This
structure corresponds to the visible part of a morel or cup fungus, although not all ascocarps are so large
and showy, or as tasty, as morels!
For an ascocarp to form, two different mating strains (+ and –) must intertwine. As they intertwine, some
of the mycelia remain haploid and sterile, growing only by mitosis. However, these haploid mycelia can
also form gametangia known as an antheridium and ascogonium, connected by a cytoplasmic bridge.
This bridge allows the antheridium to act as a ‘male’ that donates a nucleus and the ascogonium to act as
a ‘female’ that receives that donation.
At this point, plasmogamy occurs. This is fusion of two cells without fusion of the two nuclei.
Plasmogamy creates cells containing two unfused nuclei, known as a dikaryotic cells. This dikaryotic
condition is one of the distinctive, odd features of fungi and the feature is shared with the other fungal
divisions. In the Division Zygomycota (represented by Rhizopus in our lab), the dikaryotic stage is just a
single cell. The other fungal division, Division Basidiomycota, is much like the Division Ascomycota.
The dikaryotic stage forms a large, morphologically complex mycelium, which eventually forms the
fruiting bodies commonly called mushrooms. Karyogamy and meiosis occur in specialized cells within
the fruiting body.
In Division Ascomycota, this specialized structure is sac-like cell known as the ascus. Within this ascus,
the nuclei from the two mating types finally fuse (in the process of karyogamy) to form a diploid
nucleus, or zygote (2n). This zygote immediately undergoes meiosis. Each of the four haploid products
of meiosis divides once by mitosis. In a mature ascus, it should be possible to count eight haploid
ascospores 1(n). These are the cells that can be released and dispersed, eventually forming new haploid
mycelia that can start the process over again.
fall 2004, Lab 5-9
Under your dissecting microscope examine a preserved specimen of a typical woodland cup fungus,
Peziza. Where are the asci produced? Now examine a prepared slide showing a cross-section through
the ascocarp and identify the sterile hyphae, asci, and ascospores. How many spores does a mature
ascus of Peziza contain? Sketch what you see in the appropriate boxes on the life-cycle diagram on
Worksheet Two.
In many species the ascospores are dispersed by being shot out of the ascus. In open ascocarps like those
of Peziza they may be further dispersed out of the cup by wind or rain. However, the ascocarps of
truffles grow hidden underground. How do you think their ascospores are dispersed? If you need a hint,
ask your TA or lab instructor how truffles are found.
Many ascomycetes reproduce asexually and produce spores called conidia borne on the tips of modified
hyphae. These structures are well illustrated by Penicillium, the genus that is the natural source of the
antibiotic penicillin. Penicillium is also notable because the organic acids from some species provide the
flavor in Roquefort and Camembert cheese.
Examine a prepared slide of Penicillium conidia under the microscope. Observe the chunk of blue
cheese. Although theoretically it is possible to see the conidia from the cheese under the microscope, in
practice the cheese makes it a bit too mushy to see clearly. Imagine the presence of the conidia in the
cheese and next time a friend puts blue cheese crumbles or dressing on her salad, be sure to point out the
presence of living fungi.
Division Ascomycota continued: Yeasts
Not all fungi are multicellular and form hyphae. One very important unicellular group is the yeasts.
Most yeast species are Ascomycetes, as indicated by their production of asci and ascospores. With their
ability to break down carbohydrates into carbon dioxide and alcohol they are exceptionally valuable
economically, and several species have been domesticated for use in baking and the production of beer
and wine. Recently yeasts have taken added significance as model organisms for studying the molecular
biology of eukaryotes, thereby extending the work on simpler, bacterial models like E. coli to organisms
more like us.
Make a wet mount of a VERY small bit of an active culture of Saccharomyces cerevisiae, the common
bread yeast, and examine it under your microscope. Draw some of the cells, and note the asexual
reproduction by budding, the formation of small daughter cells growing out from the parent cell.
fall 2004, Lab 5-10
E. Division Basidiomycota (Kingdom Fungi)
The basidiomycetes include most of the organisms commonly called mushrooms. This division also
includes puffballs, shelf fungi, and two important groups of plant pathogens that cause extensive damage
to many crops and ornamental plants, rusts and smuts.
The distinguishing feature of the division is the club-like reproductive structures, the basidium (plural
basidia), which produce the haploid basidiospores. The spores can be seen in mass with the naked eye in
a spore print. Remove the cap from the common grocery store mushroom Agaricus campestris (or
another species if available), and place it on a piece of paper. Leave it undisturbed for students in
tomorrow's lab. Carefully lift the caps that have been left for you by the previous lab section (or by your
instructor if you are in a Monday lab section), and note the color and pattern of spores shed from the cap.
Spores are characteristic of each species and are commonly used in mushroom identification.
The structure producing the basidia is called basidiocarp and is composed of a secondary mycelium.
This mycelium is produced by the fusion of compatible strains of haploid primary mycelium, and hence
it is dikaryotic. In the secondary mycelium the haploid nuclei (one from each strain) remain separate,
dividing simultaneously as the hyphae grow and expand to form the mat of strands you might see in a
rotting log. Recall that this dikaryotic condition also occurred in the ascomycetes, but it is much more
extensive and lasts longer in the basidiomycetes. Only when the secondary mycelium aggregates to from
a basidiocarp (which may be months or years after the primary mycelia fused) do haploid nuclei in the
immature basidia finally merge, then immediately undergo meiosis to form the basidiospores.
Look at the underside of the basidiocarp of Agaricus, and note the gills commonly associated with
mushrooms. Where are the basidia located in this type of basidiocarp?
To see the basidia and individual basidiospores, examine a prepared slide of a section through a
basidiocarp of Coprinus, a common dung mushroom. (Look again at the live specimens to orient yourself
and figure out the plane in which the basidiocarp was sectioned.) Sketch some mature basidia with
spores in the appropriate square in the life cycle diagram on the your worksheet.
Like the ascomycetes, basidiomycetes have a zygotic life cycle, and only the zygotes in the immature
basidia are diploid.
fall 2004, Lab 5-11
Name ___________________________________Day/Time/Instructor ___________________________________
BC Bio 2003
Fall 2004
LAB 5, WORKSHEET 1: ISOGAMY, OOGAMY, AND COMPARATIVE BIOLOGY OF ALGAE,
PLANTS, AND PHOTOSYNTHETIC CYANOBACTERIA and
WORKSHEET 2: KARYOGAMY AND DIKARYOTIC CELLS IN FUNGAL LIFE CYCLES
A. Mating in Chlamydomonas
1. Draw what you see on each of your slides. Be sure to draw neatly using a sharpened pencil and to
record the total magnification for each.
before fusion (all strains
should look the same)
strain A + strain B
total
magnification
strain B + strain C
strain A + strain C
2. Based on your observations, which two strains are the same and which one is different?
fall 2004, Lab 5-12
B. Oogamy in Oedogonium
1. Sketch representative strands of this filamentous green alga. Be sure to identify, illustrate, and label
the structures involved in sexual reproduction (the sperm-containing antheridia and the egg-containing
oogonium). Record the total magnification.
total
magnification
2. Does the process by which the oogonium makes eggs involve mitosis or meiosis?_______________
3. Does the process by which the antheridia makes sperm involve mitosis or meiosis?______________
4. Compare the Oedogonium gametes to those you saw for Chlamydomonas. How do they differ?
fall 2004, Lab 5-13
C. Zygomycota sexual reproduction in Rhizopus
1. Clearly label a “thallus,” “hypha,” and “mycelium” on the diagram below.
2. Make a sketch of the heterokaryotic Zygosporangia you see under the microscope in the appropriate
place on the diagram below.
3. Sketch a Sporgangium you see under the microscope in the appropriate place on the diagram below.
4. Label the two parts of the life cycle (A and B) as “sexual reproduction” or “asexual reproduction.”
A
total
magnification
total
magnification
B
Figure 31.7. The life cycle of the zygomycete Rhizopus (black bread mold). 1) Neighboring mycelia of
opposite mating types (designated + and -); 2) form hyphal extensions called gametangia, each walled
off around several haploid nuclei by a septum; 3) The gametangia undergo plasmogamy (fusion of
cytoplasm), forming a heterokaryotic zygosporangium containing multiple haploid nuclei from the two
parents; 4) This cell develops a rough, thick-walled coating (upper right LM) that can resist dry conditions and other harsh environments for
months; 5) When conditions are favorable again, karyogamy occurs. Paired nuclei fuse, followed by meiosis; 6) The zygosporangium then
breaks dormancy, germinating into a short sporangium that ; 7) disperses genetically diverse, haploid spores; 8) These spores germinate and
grown into new mycelia; 9) Mycelia of Rhizopus can also reproduce asexually by forming sporangia (lower left LM) that produce
genetically identical haploid spores. [From Campbell, 6th edition, p. 621.]
5. What structure within the Rhizopus colony gives the fungus its common name “black bread mold”?
6. Both the zygosporangia and sporangia produce haploid spores, but how do they differ in function, i.e., what
different purposes do they serve in the life cycle?
fall 2004, Lab 5-14
D. Zygotic meiosis and dikaryota in the Ascomycote Peziza (Please observe the whole organism on display
even though you don’t need to draw it whole.)
1. An immature ascus contains the only truly diploid cell in the life cycle, the zygote. These immediately
undergo meiosis to produce haploid ascospores that are discharged when the asci mature. What kind of
life cycle does this represent?
2. Define plasmogamy and dikaryotic.
3. In Peziza, in what structure are the asci produced?
4. Identify and clearly label a mycelium, sterile hyphae, asci, and ascospores on the diagram below.
5. How many spores does a mature ascus of Peziza contain? (one, few, or many) ________________
6. Sketch a group of asci, their ascospores, and their associated hyphae in the appropriate place on the
diagram below.
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from Campbell, 6th edition, p. 623
fall 2004, Lab 5-15
7. The ascocarps of truffles grow hidden underground. How do you think their ascospores are dispersed?
Penicillium conidia
1. Sketch a Penicillium conidium from the
prepared slide that you saw under the
microscope.
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3. From your observations of conidia, and the asexual spores of Rhizopus, why do you think these molds
are so successful at contaminating food stuff?
Asexual reproduction in yeast
1. Note that yeast cells are very small. It will be difficult to see any internal cellular structure. The cells
tend to clump together, but this is not related to reproduction. Sketch several yeast cells in the space
below. Be sure to draw and label at least one cell undergoing asexual reproduction by budding, the
formation of small daughter cells growing out from the parent cell.
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fall 2004, Lab 5-16
E. Division Basidiomycota
1. Where are the basidia located in the Agaricus basidiocarp?
2. a. From your observation of prepared Coprinus slides, sketch some mature basidia containing spores
in the appropriate square in the life cycle diagram.
b. Sketch a basidocarp (from your observation of a live one) in the appropriate square.
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from Campbell, 6th edition, p. 625)
3. How many spores does a mature basidium of Coprinus produce? (one, few, or many) __________
4. Are the spores enclosed by the basidium? circle one: yes or no
5. a. When you eat mushrooms on your pizza, what kind of fungal tissue are you eating [is it haploid,
diploid, dikaryotic, or a combination of these (if it’s a combination, what kind of combination)]?
b. What is the MAJORITY of the tissue of a mushroom on your pizza?
6. Do mushrooms have a life cycle with gametic meiosis, zygotic meiosis, or sporic meiosis?
fall 2004, Lab 5-17