17.3: Pre-lab Questions - Biology

17.3: Pre-lab Questions - Biology

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17.3: Pre-lab Questions

Lab 7 Sample 3 Fruitflies

Drosophila Melanogaster, the fruit fly, is a great organism for genetic use because it has simple food requirements, occupies little space, is hardy, completes its life cycle in 12 days, makes a large number of offspring, can be knocked out easily, and it has many types of hereditary variations that can be seen with low power microscopes. Drosophila has a small number of chromosomes, four pairs. They are easily located in the large salivary glands. The Drosophila can be obtained from many places. Research of Drosophilae has led to a lot of knowledge about many of its genes.

Many factors combine to affect the length of the Drosophila life cycle. Temperature affects the life cycle the most. At room temperature the average life cycle of the Drosophila is about 12 days. Eggs of the Drosophila are small, oval shaped, and have two filaments at one end. They are usually laid on the surface of the culture medium, and with practice, can be seen with the naked eye. After one day the eggs hatch into the larva.

The larval stage of the Drosophila eats all the time. Larvae tunnel into the culture medium when they eat. The larva will shed its skin as it increases in size. In the last of the three larval stages, the cells of the salivary glands contain giant chromosomes that can be seen under low power in a microscope.

The pupal stage. Before a larva becomes a pupa it climbs the side of the container. The last larval covering then becomes harder and darker, forming the pupal case. Through this case the later stages of metamorphosis to an adult fly can be seen. In particular, the eyes, the wings, and the legs become visible.

The adult stage. When metamorphosis is over, the adult fly emerges form the pupal case. They are fragile and light in color and their wings are not fully expanded. They get darker in about an hour. They live about a month and then die. A female refrains from mating for about 12 days after she emerges from the pupal case. After she mates her receptacles contain large amounts of sperm and she lays her eggs. Make sure that the first flies you use are virgins.

The experiment will take several weeks. You will be assigned Drosophila with well-defined mutant traits by your teacher. You will keep a close record of what happens as each of these flies mate and pass there traits off to their offspring over a few generations.

There are three types of crosses that are studied in this lab. In monohybrid crosses the mode of inheritance is determined when a single contrasting pair of characteristics is involved. In a dihybrid cross the mode of inheritance is determined when the two pairs of contrasting of characteristics are considered simultaneously. In a sex-linked cross the mode of inheritance is determined when the mutant characteristic is associated with the X chromosome.

In the sex linked cross of Drosophila Melanogaster, a phenotypic ratio of 1:1 will be obtained.

The materials used in this lab are as follows: a vile of Drosophilia with c designated trait, vials containing a medium, a refrigerator, ice packs, Petri dishes, a light microscope, a vial of wild type flies, an incubator, a pencil and paper.

Begin by obtaining a vial of wild type flies. Practice immobilizing and sexing these flies. Make sure to examine the flies and determine the characteristics of their eyes, wings, bristles, and antennae. Next, these are the steps for immobilizing the flies. Hold the vial containing the flies at an angle and place it in a refrigerator for several minutes. When the flies are immobilized, place them into a small plastic Petri dish. Then place the Petri dish on top of the icepack in order to maintain the cool temperature necessary to keep flies immobilized. Use the dissecting microscope to view the flies. Make sure to top the petri dish on when viewing the flies.

You can easily distinguish male flies from females by looking for the following characteristics: males are usually smaller than the females, males have dark blunt abdomens and females have lighter pointed abdomens. The males have sex combs, which are black bristles on the uppermost joint of the forelegs. Next, get a vial containing experimental flies. Make sure to write down the number of the vial that you have. The flies you now have are the P1 generation. The females should have laid eggs. The eggs and larvae are the F1 generation. Then after there are eggs present knock out remove the adult flies from the vial. Sex the adult flies and write down any mutations. Place the flies in the morgue that contains alcohol. Make sure to label the vial with the symbols for the mating.

After about another week has passed knock out and record characteristics of the remaining F1 flies and record the results in table 7.1. Then place the six pairs of these flies in a new vial and place the remaining flies in the morgue. Label the new vial F1, and tell the cross, date and your name.

After another week has passed, remove the F1 flies and put them in the morgue. The F2 generation are the eggs and larvae in the vial. Place the vial back into the incubator. Once again, after another week has passed remove the F2 flies and record their sex and characteristics and place the results in Table 7.2. Recording a greater number of F2 flies will make your results more accurate. Try to collect at least 200 flies. In order to analyze your data you will first have to be able to be able to complete Chi-Square Analysis.

17.3: Pre-lab Questions - Biology

Key Dates
Release Date: May 31, 2017

Issued by
National Institutes of Health (NIH)
Agency for Healthcare Research and Quality (AHRQ)

This Notice provides reminders for research grant applicants and mentored career development award applicants that propose the use of key biological and/or chemical resources. As described in NOT-OD-16-011 and NOT-OD-16-012, applicants proposing the use of established key biological and/or chemical resources are expected to include a plan to authenticate these resources in the "Authentication of Key Biological and/or Chemical Resources" attachment.

"Key biological and/or chemical resources" refers to established reagents or resources that will be used in the proposed research. This includes but is not limited to cell lines, specialty chemicals, antibodies or other biologics. Key biological and/or chemical resources are integral to the proposed research and may or may not have been generated with NIH funds.

Key resources that require validation are likely to:

  • Differ from laboratory to laboratory, or over time
  • Vary in qualities or qualifications that could influence the research data

Applicants proposing to use established key biological and/or chemical resources are expected to include an authentication plan in the "Authentication of Key Biological and/or Chemical Resources" attachment, even if the key resources were purchased or obtained from an outside source that provided data on prior authentication. The authentication plan must include only a description of the methods proposed to authenticate key resources prior to use and at regular intervals, if appropriate. The plan should be no more than one page.

  • Applicants proposing to use cell lines could describe the method they plan to use to verify the identity and purity of the lines, which might include short tandem repeat (STR) profiling and mycoplasma testing.
  • Applicants proposing to use chemicals that are key to the research could describe the method used to validate the chemical, which might include liquid or gas chromatography, or mass spectrometry.
  • Applicants proposing to use genetically modified animals or cells could describe the method used to confirm the genome modification, which might include PCR amplification or Southern blot.

When published consensus standards exist, these may be cited in this section as the procedures that will be used for validation.

The "Authentication of Key Biological and/or Chemical Resources" attachment is only for established key biological and/or chemical resources.

  • Do not include plans for authentication of data sets, databases, machinery, or electronics in the "Authentication of Key Biological and/or Chemical Resources" attachment.
  • Do not include plans for the development and authentication of new key biological and/or chemical resources (such as a new human cancer cell line or a new antibody). Applicants proposing to generate a new key biological and/or chemical resource must describe the development and authentication of the resource in the Approach section of the Research Strategy.
  • Do not include plans for authentication of standard laboratory reagents that are not expected to vary. Examples are buffers and other common biologicals or chemicals.
  • Do not include authentication or other data in the "Authentication of Key Biological and/or Chemical Resources" attachment. Include only a description of the methods proposed to authenticate key resources.

Reviewers will discuss the information provided in this section after the application has been scored. Any reviewer questions associated with key biological and/or chemical resource authentication will need to be addressed prior to award.

Information in this section must focus only on authentication and/or validation of key resources to be used in the study as described above. All other methods and any data must be included within the page limits of the research strategy. Applications identified as non-compliant with this limitation will be withdrawn from the review process (see NOT-OD-15-095).

17.3: Pre-lab Questions - Biology

Name ______________________________________ Section _____

Pre-lab Questions - Microscopy

1. List 3 contributions of Antony von Leeuwenhoek and 3 contributions of Robert Hooke to the
science of biology?

2. Briefly describe in your own words, how a phase contrast microscope works? What is its use?

3. Briefly describe in your own words, how a transmission electron microscope works?

4. Briefly describe in your own words, how a scanning electron microscope works?

5. List the function of the following parts of the microscope.

Body "tube" _________________________________________________________

Mechanical stage ____________________________________________________

Mechanical stage knobs _______________________________________________

Stage clip(s) ________________________________________________________

Rotating nose piece __________________________________________________

Iris diaphragm _______________________________________________________

Illuminator (light source) ______________________________________________

Objective lenses _____________________________________________________

Coarse adjustment knob _______________________________________________

Fine adjustment knob _________________________________________________

6. What is meant by total magnification?

7. What is meant by parfocal?

8. Using resources available to you, find and attach a representative photomicrograph of a
biological specimen taken by Compound Light Microscope, a TEM (transmission electron
microscope) and an SEM (scanning electron microscope). This does not mean a picture of the

10. List at least three different types of microscopes that are used by biologists to study cells.

The United States Medical Licencing Examination materials for Step I are already available at the USMLE website.

The materials can be downloaded in pdf format in:

The content outlines for this exam has been updated by a subcommittee of the step I committee.

The updated content can be found in this link:

USMLE committee recommends to students considering to exam Step I after May 2011 to be familiarized with the previous (2010) and the updated content outlines.

In future posts we will discuss the topics associated to the sample questions related to Biochemistry that are included in these materials.

Watch the video: 3 Secrets of Ovulation Bleeding (July 2022).


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