TITLE - EXAMPLE LABORATORY REPORT
TITLE - EXAMPLE LABORATORY REPORT
Biology #181 Sections #...
Laboratory Report #
Name
Partners
TA Angie Huxley
ABSTRACT:
This experiment demonstrates both cell division and genetics. Various
stages of mitosis, prophase, metaphase, anaphase
and telophase are easily identified from fish eggs and onion tip cells.
Stages of meiosis including synapsis, metaphase, and
telophase, are located and identified in grasshopper testis. Corn plants
are used to demonstrate the genetics of corn breeding for a monohybrid
and dihybrid cross. The results of the monohybrid crosses for color are
significantly different than the expected ratios, suggesting counting error,
sampling error, or insertions of genetic information from transposons.
The kernels from the dihybrid cross also vary significantly from the expected
ratio. The observed ratio is 14.5:2:6.5:1 and the expected ratio is 9:3:3:1.
Some of the same sources of error discussed above may also be operating
in the dihybrid cross as well. Finally, wild-type and dpy-20 nematodes
demonstrate that a single mutation can affect the phenotype of the organism.
This experiment is relevant since it shows that observational data may
not correspond exactly with theoretical calculations in monohybrid and
dihybrid crosses.
Limit words in the abstract to one hundred if possible, but say what must be said about the experiment including introduction, purpose, results, and implications. This must be done in present tense.
INTRODUCTION:
Cells must be capable of replication. Both mitosis, cell division
for replacement of tissues, and meiosis, cell division for germ cell production,
are essential for the continuation of life. These cells, if unicellular,
must interact directly with the environment, and in doing so, are limited
by the environment. These cells, if multicellular, must interact
to maintain the internal needs of each individual cell as well as the group
of cells to maintain the internal environment of the organism. All
cells go through similar processes to accomplish these goals -- a division
process that involves replication of the genetic material, division of
the cytoplasm and intracellular organelles, as well as a method by which
to recombine genetic material.
The purpose of this particular laboratory experiment is to identify the phases of mitosis -- prophase, metaphase, anaphase and telophase -- from histological samples of onion tip and fish blastula through the use of a microscope; to attempt to distinguish histological features of meiosis from grasshopper testis through the use of a microscope; and to analyze the results of monohybrid and dihybrid crosses of corn through counting kernels of corn.
Please note that the purpose and the method of examination are listed in this section. This section requires two paragraphs, a general introduction to the topic and a brief description (purpose) of what will be discussed in the paper.
EXPERIMENTAL PROCEDURES:
Refer to the laboratory manual pages .....
Only itemize the procedures if there is a change from the laboratory manual.
RESULTS:
In the section on cell genetics, mitotic stages from the fish blastula
are not easily observable under 10 and 40 power;
however, at 100 power, they are identified as prophase, metaphase,
and telophase. The onion tip was easily identifiable under all powers (except
oil immersion) and all stages of mitosis are viewed. The grasshopper testis
is most readily seen under 40 and 100 power. Cells in synapsis, metaphase,
and telophase are noted.
Fish Blastula- drawings, with label, scale and preparation technique
The drawings represent each of the stages of mitosis with the exception
of anaphase, since it cannot be located.
Onion Tip Drawings - drawings, with label, scale and preparation technique
The drawings represent each of the stages of mitosis.
Grasshopper Testis - drawings, with label, scale and preparation technique
The drawings represent synapsis, metaphase and telophase of meiosis
from grasshopper testis.
Corn Genetics
In the section on corn genetics, the experiment begins with two homozygous
parents, one parent was purple and
homozygous dominant for the alleles (PP). The other parent is yellow
and homozygous recessive (pp) for the alleles. These
parents are crossed and a heterozygous offspring (Pp), purple in color,
is produced. A test cross is then conducted to
determine the genetic constitution or genotype of the F1 generation
as determined from the phenotype by mating
back to the parent with the recessive alleles. The heterozygote F1
(Pp), purple in color is crossed with the homozygous
recessive (pp) parent, yellow in color.
Punnett's Square Here
This monohybrid cross produces two colors of offspring, purple and yellow
in an expected ratio of 1:1. Yet, while counting
kernels from the monohybrid cross, the ratios are not the same.
Kernel Color Tally Total Genotype Calculations
Purple 105 155 Pp 105/50 = 2.1
Yellow
50 155
pp 50/50 = 1
The observed ratio is 2.1:1. There are several reasons why these ratios
are not the same. For instance, some kernels
appear very small and shrunken indicating early selection against certain
phenotypes, miscounting of kernels may
occur, and sample sizes are relatively small, suggesting sampling error.
Next, two heterozygote F1 offspring are crossed to each other. Each
F1 heterozygote is genetically (Pp) and purple in
color. A Punnet's square is developed to find expected genotypic and
phenotypic ratios for the offspring. The genotypic ratio is 1:2:1, while
the phenotypic ratio is 3:1. This suggests that 75% of the F2 kernels will
be purple in color, while 25% will be yellow in color.
Punnett's Square Here
Observations do not reveal a 3:1 phenotypic ration, but rather a 4.5:1 phenotypic ratio.
Kernel Color Tally Total Genotype Calculations
Purple 198 242 PP, Pp 198/44 = 4.5
Yellow 44 242 pp 44/44 = 1
This ratio may be due to the events listed above, or possibly due to
transposons, which move genetic information from one
gene to another.
The dihybrid cross is carried out for two traits, plump (S-) vs. shriveled
(ss), and purple (P-) vs. yellow (pp). The
expected ratio is developed from the following Punnet's square.
Punnett's Square Here
The expected phenotypic ratio is 9:3:3:1. This reflect 9 plump and purple, 3 plump and yellow, 3 shriveled and purple, and 1 shriveled and yellow.
Kernel Shape and Color Total Calculation Proportion
Plump and Purple 406 406/28 14.5
Shriveled and Purple 56 56/28 2
Plump and Yellow 182 182/28 6.5
Shriveled and Yellow 28 28/28 1
The progeny is then counted to reveal that the expected ratio of 9:3:3:1
does not match the observed ratio of
14.5:2:6.5:1. These counts do not support the expected ratio, indicating
observer error in counting,
misclassification of shape and color due to transposon interference,
zygotic and developmental selection against
certain phenotypes, and statistical error due to a small sample size.
Moreover, incidence of transposable element
expression is approximately 55% in the ear of corn for the monohybrid
cross. Expression is either large spots of
opposite color, splotches of color interspersed in a second color,
or stripes through the kernel.
Finally, two nematodes are studied microscopically for variation in
phenotype due to a mutation called dpy-20. The first
nematode in normal, wild type. This organism is long, thin and moves
in a gliding fashion. Dpy-20 is fat, short and
moves in a more linear motion. This demonstration reflects the fact
that a single mutation in a gene can result in
alterations of the phenotype of the organism. This section should include
all of your results. All data must be
reported. Inferences can be made later. Notice that I highlighted information
called for in the laboratory manual, so
that this information is distinct from background information.
DISCUSSION:
The cell division section demonstrates the differences between mitosis,
used for the replacement of soma, or general body
cells, as distinct and separate from the process of mitosis for the
production of gametes. The stages are essentially the same, while the processes
and ends are different. While mitosis results in the production of two
identical daughter cells, meiosis results in the production of four non-identical
daughter cells that have quite a bit of variation. The slides demonstrate
key stages for each of these processes.
The monohybrid cross illustrates the inheritance of alleles culminating
in the genotype, and expressing itself in the phenotype
for a single variable, color. Next, a dihybrid cross is performed for
two traits, physical characteristics and color. While
expected and observed ratios are not the same, several sources of discrepancy
are possible. Observer error is noted in at
least one instance. Sample sizes are very small. With an increase in
sample size, the phenotypic proportions will be more
closely matched. Phenotypic selection may occur, as some kernels are
very small and shriveled.
Next, transposons may insert genetic information into kernels of opposite
color, thereby influencing protein synthesis and
affecting classification of phenotype. All of these factors may be
responsible for the variation between expected and observed ratios.
Finally, a wild-type and mutated dpy-20 nematode, are studied in a nematode to demonstrate that a single mutation can lead to alterations in the phenotype of an organism.
In the discussion section, you want to place this laboratory into a larger theoretical framework. What is this lab intended to do? Did this lab accomplish those ends? Did your experiment come out as planned? Or, did something go wrong? How do you explain discrepancies?
REFERENCES CITED:
Fishel BR, Grimes WJ, Hallick RB, Holstein TE, Baker RO (1999) Biology 181 Laboratory Manual Fall 1999m Hayden McNeil Publ., Plymouth, Michigan, pp.....