Formal Dihybrid Cross Report

Instructions:

• One inch margins. Font: Times New Roman, size 12. Page Number at bottom.

 

General Guidelines:

• Please READ your lab manual carefully. Understand what you did BEFORE you start writing!
• Instructions on the general format of a lab report are found on pg. 7 in your lab manual.
• In lab reports, ALWAYS use the past tense.
• Use clear and concise language.
• Do not write your lab reports with your partners. Your report should be written only by you.
• Any figures or tables must be labeled and described clearly (see below). They are meant to clarify the text, and should be referred to in your results and discussion; do not just leave a figure hanging.
• Clearly define each section (Introduction, Materials and Methods, Results, Discussion).

 

For Figures and Tables:

            Directly Underneath each figure or table there must be the number, a title, and then an explanation.

For Example:

 

Figure 1. Branch diagram of predicted genotypes/phenotypes of the Corn Cross. The diagram predicts a phenotypic ratio of 9:3:3:1 (Green: Yellow-Green: Yellow-White: White)in accordance with Mendel’s laws for a dihybrid cross.

or:

Table 1. Scoring Results of Corn Seedling Cross. Plants were scored visually resulting in only three observed phenotypes: Green, Yellow-White, and White.

 

Title:

Do not use the one from the lab manual. The title should appropriately describe the experiments in a concise way. Under the title, include your name, the names of your group members, the date, lab section, and TA.Do NOT use a whole page for the title.

 

Introduction: (This section answers why you did the experiment.)

State briefly what the purpose of the lab was and describe the main theme of the experiments. DO NOT copy the lab manual.

Briefly state what the corn cross was,both genotypically and phenotypically. Write out the alleles for each gene and describe the phenotype. For example, w3 is recessive and is responsible for white color of seedlings. Descriptions for each gene are in the lab manual. Give also the location for each gene (also in themanual).What are Mendel’s laws? How do they apply to dihybrid crosses? How are they applicable to this lab? Name and describe 2 ways in which standard Mendelian ratios may be modified.What did you expect to find for this cross: a standard or a modified ratio? State your null hypothesis in precise terms.

 

Materials and Methods: (This section answers how you did the experiment and how you evaluated the data.)

State clearly what you did in a concise way.

Diagram the corn cross from the inbred parents through the F2 generation–Show branch diagram figures or punnett squares, giving phenotypic and genotypic result ratios. Describe how you came up with your null hypothesis. Then, describe how you scored the cross and how you pooled data. Explain how Chi-square is used to evaluate the null hypothesis, including the formula and how you determined the expected values. How did you choose the degrees of freedom? How did you get the χ² number? How is the χ² number used in conjunction with the degrees of freedom to determine the p-value? Whatdoes the p-value mean (i.e. what does it tell you about chance variation)? When should the null hypothesis be accepted or rejected? Once you have explained Chi-square, you should state in your own wordsthat Chi-square was used to determine the validity of your null hypothesis. Don’t tell me yet whether or not your null hypothesis was accepted or rejected–SAVE THAT FOR THE RESULTS! Do NOT show me your chi-square results yet,they belong in the results section.

 

Results: (This section answers what you found. Save interpretation for the discussion.)

Results must be described in words in paragraph form; tables and figures alone are not sufficient.

Generate a table for your Chi-square analysis used in the lab (pg. 26in the manual has an example). Describe in sentences how you tested your null hypothesis.Don’t forget to include your p-value and state whether you rejected the null hypothesis or not. The chi-squaremay be done in excel, but show me the steps. Save any lengthy explanation for the discussion. Be brief. State only what your data shows.

 

Discussion: (This section explains what it all means.)

There were several questions and important comments noted throughout the description of this lab. Many of these would be good points to incorporate into any discussion of your experiments. Review these as you begin the writing of your report, particularly the discussion.

 

Here you should analyze the cross, explaining what you think was going on to give you those results. To do this, first restate the result of your cross; then explain why you think your hypothesis was accepted or rejected.Describe any complications that may have affected the result.If you rejected your null hypothesis, propose a new experiment that would help clarify the cause of the rejection. Once you have finished analyzing the cross, describe what was demonstrated by these experiments, as well as your conclusions from the experiment. DO NOT make personal statements such as, “I thought this lab was hard because…” We are not asking for your critique of the lab (you can do that in the course evaluations at the end of the semester). We are asking that you discuss the biological processes, expectations and outcomes of these experiments.