DrosophilaThree-Point TestCross Lab Write-Up Instructions(65points)
Abstract (5 points)
In a short paragraph describe the experiment that was done as well as the major findings. Clarity is essential. Theabstract is usually written last and is limited to 200 words.
Introduction(14points)
Provide ALL background information a reader would need to understand thepurpose results and analysis of theexperiment. Must include:
1.Why itisimportant to know the locationsof genesin the genome.
2.A description a crossing-over during meiosis linkage recombination frequency (RF)and howRFrelatesto map units?How does RF change forcloselylinkedversusdistantly linked and unlinkedgenes?
3.Why is it advantageousto mapthree (or more)genes at once instead of mapping each pair of genes separately
4.The benefitsofDrosophilafor genetic analyses
5.Thehypotheses for this experiment
RF measured in lab will be similar to the expected RF based on known map distances.
Reciprocal classes will occur and survive in equal numbers.
Interference will be a positive value.
Methods(14points)
This section should provide enough information so that the reader could carry out the experiment independently.
1.Explain the experimental strategy: P F1and F2. Describe all genotypes and expected phenotypes.
2.Describe the different traits that werescored.
3.Why was it unnecessary to determine the sex of the F2?
4.Describe calculations for RF map units and Interference.
5.Describe the Chi-Square tests that were done and the highest acceptable Chi-Square value for acorrespondingp value of 0.05or lowerfor relevant degrees of freedom used in your differentChi-Square tests. (Measured vs. published map distances; reciprocal classes)
Results(14points)
In this section the data are shown in tablesANDexplained in coherent paragraphs.
1.Producea tablewith thecountsof eachF2phenotype for:your groups data your lab sections data data provided by the fly experts.(Note to TAs:This lab has a long history of terrible dataso each lab instructor will invent a dataset for eachof her/his lab sections.These data sets MUST change each semester!)
2.ProduceTHREEgenetic maps each based oneach ofthe data sets in the Table. Calculate Interference for each data set.Show the equation for calculation of interference.
3.Compare expected and observed data for pairwise map distances among the three genes and for reciprocal crosses usingChi-Square values.Report p-values for all comparisons and state whether differences between expected and observed data can be attributed to chance.Do this for all data sets. (There will be 18 Chi-square calculations 6 per data set.)
4.A narrative must describe the table mapping calculations and Chi-Square calculations. You must interpret your Chi-Square results. Can deviations from expected values be attributed to chance? Explain your reasoning.
Discussion(14points)
The results are summarized in this section and the reasons WHY data were significantly different than expected are considered.
1.How do map units calculated from the three data sets(one small and two large)compare to published distances?
a.What happened for the shorter y-cv distance?
b.What happened for the longer cv-f distance?
c.What happened with the 4 reciprocal classes? In the case of reciprocal classes were any trends observed (certainreciprocalstend to be near equal while others were quite different)?How do mutations affect viability?
d.Did these results match the hypotheses stated earlier?
2.Why is it difficult to accurately measure long map distances by RF?
a.What can be done for more accurate measurements of long map distances?
3.What difficulties arose when assigning phenotypes when scoring the F2?
a.What could be done to reduce these difficulties?
Overall Conclusions(4points)
Keep this section short one paragraph at the most. Do not repeat yourself over and over when writing this paragraph!
What do the data demonstrate?
Why is a statistical analysis important?
Summarize ways to improve the outcome of the three point testcross mapping experiment; describe tricks for evaluating phenotypes.
PLAGIARISM:Rememberyou must use your own words even if you work with others to discuss what the content of your paper will be. Do not use quotations; read material figure out what it means andthen explain in your own words. If you do use material not found in the lab manual or the textbook be sure to cite it. Instructions for citations are found in the oral presentation section of the Genetics Lab Manual. All papers must be .doc or .docxfiles and will be submitted to your labs BeachBoard Dropbox and will be subject to plagiarism detection usingTurnitin. A strict ZERO policy (on the entire write-up) will apply to allplagiarism that goes beyond a shared common phrase.If two students papers are found to be highly similar BOTH students will receive a ZERO. Do not give your word file to a friend to help them out at the last minute; they will likely take both of you down.Papers must be uploaded to the labBeachBoardDropbox BEFORE your lab starts on the designated due date.Please seehttp://philosophy.tamu.edu/~gary/intro/plagiarism.index.htmlfor some examples of plagiarism.
Citations
To respond to question 1 of the Introduction you will need to look up papers. Cite these as described in the group oral presentation instructions in the Genetics Lab Manual.
Writing Tips
Many students feel that if they write something in complicated language they sound more intelligent. This results inawfulsentences such as A significant frequency of DNA is made of gene. Genes are made of DNA. makes a lot more sense!Also the term significant is only used with an accompanying statistical test. See below for more helpful writing tips:
1) The phrasingso… is conversational English and not appropriate for written English.
2) The word very has little meaning. Use a stronger adjective. Four letter V-WORD.
3) Use the passive voice not We definerecombination frequencyas… Instead use: Recombination frequency isdefined as…
4) Separate different sections into paragraphs so the overall organization is clear to the reader.
5) If you want to use it or they in a sentence be certain that the subject referred to is clear.
6) Omit needless words. Go through each sentence to reduce wordiness.
7) its = it is; its is the possessive.
8) Do not keep using the word it in your complex sentences. Re-word the sentence so the subject is clear.
9) Avoid meaningless sentences such as Chromosomes areinteresting moleculesthatarefound inDrosophila. Think of a real point you want to make and use meaningful language.
10) Avoid contractions; dont use them! I cannot emphasize this enough; theyre too informal.
11) Semicolons separate two independent clauses; independent clauses can serve as their own sentence.
12) A colon separates one independent and one dependent clause: as in this sentence.
13) The possessive is rarely used in scientific writing and comes off as awkward and unprofessional. Do not write Thegeneslocation is not known. Instead write Thelocation of the gene is not known.