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Inherited Traits in Humans and Fruit Flies

Author(s): Terion Grifiths M.A., and Erin S. Kelleher, Ph.D.
Inherited Traits in Humans and Fruit Flies
  • Grades:
  • Length: Variable


Students will perform crosses between fruit fly strain with different physical characteristics and observe 1) the transmission of traits from parents to offspring and 2) that offspring produced by sexual reproduction exhibit diverse combinations of parental traits. This updated version streamlines and simplifies the experiments to make them more accessible to 7th grade students.

Teacher Background

Students will work in groups to explore different traits in fruit flies using microscopes, taking advantage of stations you set up before class. The students should work together to identify and record traits that differ among the flies. They should observe that the flies can have either red or white eyes, and that the flies can have either straight or curly wings. After about 5 minutes of observation, you lead them in a discussion of their observations. PowerPoint slides 6 and 7 include photographs of red vs white eyes, and curly vs straight wings. Some students may notice other traits that vary, in particular the darker abdominal pigmentation of male flies.


Objectives and Standards

Conceptual Learning

  • Heredity is the passage of genetic instructions from one generation to the next, through chromosomes contained in gametes.
  • Sexual reproduction results in more diverse offspring and involves the fertilization of an egg cell from one parent with the sperm cell of the other.
  • Sexual reproduction can produce diverse offspring because each sperm and egg cell contains a unique combination of parental genes.

Science, Math and Health Skills

  • Observation
  • Data Collection
  • Hypothesis Testing



7.14A: Define heredity as the passage of genetic instructions from one generation to the next generation.

7.14B: Compare the results of uniform or diverse offspring from sexual reproduction or asexual reproduction.


MS-LS3-2: Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation.


2 class periods (15 minutes setup, 45 minutes for activity); allow 2 weeks between Class Periods 2

and 3. See SETUP for options.


Materials and Setup

Items which can be purchased at Carolina Biological Supply Company (CBS) are marked with their specific product names and stock numbers, beginning with “CBS#” (

  • Drosophila media, university research labs may be able to provide a small amount of media in prepared vials with enclosures at no cost. However, you can also purchase this from Carolina Biological Supply (CBS# 173210).
  • Drosophila vials with enclosures. If you are unable to obtain from a university research lab you may purchase them from Carolina Biological Supply (CBS# 173076, 2 per group).
  • Vials containing living Drosophila melanogaster (fruit flies) are often available from university research labs at no cost. Wild-type flies, white eyed mutants and curly winged mutants are required for this activity. If you cannot locate a local lab, wild type flies with red eyes and straight wings (CBS# 172100), white-eyed mutants (CBS #172220), and curly-winged mutants (Item # 172750) are available in vials of 25–30 adults from Carolina Biological. Each adult fly is capable of producing 1-2 offspring over a span of 2 weeks, given proper care and environmental conditions. (CBS# 172100, standard red). Note that the curly-winged mutants also carry other mutations that your students may notice.
  • FlyNap® Anesthetic Kit (CBS# 173010). Each kit contains a 10 mL vial of FlyNap® (100 doses) and 12 anesthetic wands. Flies remain “napping” for 50 minutes to several hours without being killed or sterilized.
  • Vials Popsicle sticks or small scraps of paper, 2 per student.
  • Microscopes.
  • Paint brushes.
  • Photocopies of each student page, 1 set per student or student team or group.



These quick videos might provide helpful review before you teach this material. “Flynap” (; “Observing Phenotypes and Crossing Drosophila melanogaster” (; “TEDEd genetics video”


  1. 1-2 months in advance: Order fruit flies, media and appropriate supplies from a local university research lab or from Carolina Biological Supply.  If you have a lot of students and few flies, you can rear the flies yourself for 1 generation (~2 weeks) to ensure you have lots of flies to spread across multiple classes.

  2. 5 Days in Advance: You need to separate wild-type straight winged females from the adult male flies. This will ensure they do not contain sperm from any previous matings, so that your students can control the “fathers” of their baby flies. To separate the females from the males, anesthetize the fruit flies using FlyNap®. Dip the provided wand into the bottle of FlyNap®. Turn the culture vial of flies upside down, then slide wand in between the cotton and side of the vial. Continue to hold the vial upside down while the flies fall asleep and drop onto the cotton. The flies will remain asleep for 50 minutes. Diagnostic differences in abdominal coloration and genitalia between male and female flies can be found on slides 3 and 6 of the slide show. Once you have separated the females based on their sexual characteristics, place them in a separate female only vial.

  3. Class period 1: Load and open the activity’s classroom PowerPoint® slide set. You will be using Slides 1–7; Anesthetize the fruit flies using FlyNap® all the adults you need for a given class period. The critical flies for your students are the wild-type females, and their white eyed and curly winged male mates. For each group we recommend 10-20 females and 5-10 of each type of male; Divide the wild-type flies among the available microscope stations, placing a mixture of wild-type, white-eyed, and curly-winged flies at each station; Set the magnification on all microscopes to 20X. Allow students to focus the microscopes to their personal preference: Photocopy or print student sheets for (1 set per student or student group or team). Students will complete it in sections; Throw away the parents from your students' crosses. This will ensure there are not too many fruit fly larvae in the vial. Overcrowding the developing flies can lead to poor health as well as soupy fly food that is difficult to work with.

  4. Class Period 2: Anesthetize the offspring from both vials of each group in the class. Keep the offspring from each vial separate so that students may observe the independent groups of offspring produced from both sets of parents. Separate index cards or pieces of paper are good
    for maintaining the separate groups of offspring; Load and open the activity’s classroom PowerPoint® slide set. You will be using Slides 8–12.


Procedure and Extensions

Class period 1. Trait Inventory in Humans and Fruit Flies

  1. Working with a partner the students will observe 5 physical traits they exhibit, which are determined by genes they inherited from their parents. The pictures on this website might help
    you and your students determine which traits they have ( When they are done tell them the traits are genetic: transmitted from parent to offspring. In this lesson, they will be developing and testing hypotheses about how traits are transmitted from parents to offspring. Ask the students the following question: What do they
    know about the transmission of traits from parents to offspring?

  2. Project Slide 1: Tell students they will be learning about the transmission of traits from parents to offspring in humans (the Smith family) and fruit flies.

  3. Project slide 2: Remind the students about the difference between attached and detached earlobes.

  4. Project slide 3. Ask the students to consider whether the transmission of attached vs detached earlobes from parent (Will and Jada Pinkett Smith) to offspring (Jayden and Willow). Ask the students the following questions: How can Jayden have attached earlobes if both parents have attached earlobes? Why do Jayden and Willow inherit different traits (attached vs detached earlobes) if they have the same parents?

  5. Project Slide 4: Ask your students to define a hypothesis as best they can. Discuss the given definition of a hypothesis and ask your students to develop a hypothesis about how traits are transmitted from parent to offspring, which accounts for their observations of the Smith’s
    earlobes. They should write their hypothesis down on their worksheet.

Project Slide 5: Introduce fruit flies as an experimental tool used by many scientists to study the transmission of traits from parents to offspring. Ask your students the following question: What traits do they observe that differ among the fruit flies on the slide? They should observe many differences including in eye color, eye shape, wing color, wing shape, body shape and bristle appearance (body hair).


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This activity was funded by NSF Grant 1457800 to Erin S. Kelleher © University of Houston. Dissemination provided by Baylor College of Medicine via its BioEd Online Website.