How Do Traits Combine and Mix?

Sorting, recombination, chi-square, dihybrid crosses, pleiotropy, epistasis, polygenetic traits, and linkage groups

Decisions, Decisions!

A Genetics Role-playing Activity by Sharon Nelson


In this activity, you will use research/study skills to investigate a particular human genetic disorder and assume role(s) of doctor, genetic counselor, parents, sibling(s), affected individual (as the case requires). You will work cooperatively with other students and make informed decision(s) based on consideration of the bioethical issues involved. By the end, you will generate a written report summarizing the information gathered and give an oral presentation to the class, explaining your particular circumstance, the bioethical issues involved, and the decisions that were made by your group. You will defend your decisions and will answer questions posed by your peers.


Students will be assigned to work in groups of 2-5. Students will then choose a scenario for role playing. Your job is to research any and all information relevant to your situation. Students may divide the roles in any way they see fit (one may choose to assume the role of parent, another the role of doctor, etc.) Once you have the necessary information, you must make some decisions regarding your situation, based on the bioethical issues involved. In addition to a 5-10 minute oral presentation, students must, with your group members, turn in one written report.

  1. Research the genetic disease.
    1. What are the symptoms?
    2. What is the cause (or causes) of the disease?
    3. What are the treatments of the disease?
    4. What is the cure, if any, for the disease?
    5. List all resources used.
  2. Research the treatment.
    1. How much does the treatment cost?
    2. How long does the treatment take?
    3. Show, with calculations, if your patient would be able to afford the treatment.
    4. List all resources used.
  3. Prepare the genetic counselor’s report by putting yourself in the position of a professional who is counseling these parents.
    1. Why did this disease happen?
    2. What are the chances that this disease will happen again?
    3. What can be done now?
    4. List all resources used.
  4. Prepare the parent’s report by putting yourself in the position of the parent with these problems.
    1. What are the financial effects of the disease?
    2. What are the emotional effects of the disease?
    3. What are the social effects of the disease?
    4. List all resources used.
  5. Research resources available in the community.
    1. What resources are available in Northeast Ohio for education about this disease?
    2. What resources are available in Northeast Ohio for medical progress in treatment and cures for this disease?
    3. List all resources used.
  6. Conclusions.
    1. In this scenario, what decision would you make as the genetic counselor? Explain!
    2. What decision would you make as the parent? Explain!
    3. Summarize the scenario.
  7. Prepare your oral presentation.
    1. Who is going to say what?
    2. Prepare two to three pictures for display during your presentation.
    3. Practice and ensure that the presentation will last between five and ten minutes.
  8. Write your report using the rubric at the end.

Role Play Scenarios

  • Your 16-yr-old daughter is 6′ tall. After some discussion about her health and some probing by the family physician into your family’s history, you are referred to a genetic counselor. The physician suspects the possibility of Marfan’s Syndrome. Your daughter is currently on the varsity basketball team, and the season has just gotten underway.Your income: $55,000 Insurance: HMO, 80% coverage.
  • You and your wife have just lost a child to Tay-Sachs disease. You were referred to a genetic counselor before deciding to have more children.Your income: $75,000 Insurance: none
  • You and your husband are in your early forties and have decided you would like to have another child. Your physician refers you to a genetic counselor to discuss concerns regarding Down’s Syndrome.Your income: $150,000 Insurance: 80% coverage
  • You and your partner are both African American. You have two children: the second child, a girl, is an albino; the first child, also a girl, is visually impaired. You would like another child and seek the advice of a genetic counselor.Your income: $90,000 Insurance: full coverage.
  • You have one child, age 3, that has cystic fibrosis. You are three months pregnant with your second child; you and your husband separated a month ago. You have been referred to a genetic counselor.Your income: $35,000 Insurance: coverage through spouse’s employer.
  • You have just married. You and your spouse are healthy but your husband’s brother has two children with sickle cell anemia and your sister has the same disease. You are thinking of having children and have sought the advice of a genetic counselor.Your income: $51,000 Insurance: none
  • Your oldest child has PKU that was diagnosed at birth. You are unexpectedly pregnant with a second child and have been referred to a genetic counselor.Your income: $72,000 Insurance: through your employer jointly; your husband has just been laid off from his job.
  • You have hemophilia; you and your spouse would like to have children. You are referred to a genetic counselor.Income: You just lost your job due to missing so many days of work for hospital stays. Wife’s income as teacher’s aide: $18,000.Insurance: none
  • You and your wife both have achondroplasia. You have just built a house to suit your needs. You would like to have a family and have been referred to a genetic counselor.Income: $150,000. Insurance: HMO, 90% coverage
  • Gloria, 19, is married to Robert, 21, and they wish to start a family. Both of Gloria’s parents are healthy (Sonia, 39, and Todd, 40). However, Gloria’s grandfather died at the age of 43 after being diagnosed with Huntington’s Disease. Gloria and Robert have many questions and seek out a genetic counselor for information.Income: $52,000. Insurance: both, through employers
  • Jim,32, and Tammy, 28, have had two healthy children: Twila, age 3 and Terry, age 5. They have, however, recently discovered some background news about Tammy’s family that concerns them. They have just found out that a brother of Tammy’s, who was confined to a wheelchair by age 10, has Muscular Dystrophy. They would love to have a family of four children. Genetic counseling is available.Income: $80,000 Insurance: 50% coverage
  • As a result of information learned in his high school biology class, Jim thinks he may have Klinefelter’s Syndrome. His parents have never heard of this disorder and they seek out a genetic counselor.Family income: $92,000 Insurance: full major medical coverage.
  • You and your wife have two children. The first is healthy. The second has spina bifida, and is paralyzed from the waist down. You desire more children and seek the advice of a genetic counselor.Income: $200,000 Insurance: full coverage
  • Cindy, 38, is expecting her third child. She has two healthy children. Due to her age, her doctor suggests that amniocentesis be done at sixteen weeks post-conception. The karyotype reveals that the child has Turner’s Syndrome. Cindy and her husband Stan are referred to a genetic counselor with this information in hand.Income: $75,000 Insurance: self-insured

Oral Presentation:






Heard and understood by all


Everyone could hear and understand!


Some things were hard to understand


What was that again?


I have no idea

Creative approach


Truly unique


Not unique, but well put together


Haven’t I seen this before?


Did you plan at all?



No errors


A couple minor errors


Are you sure you did the research?


What research?

Participation of all members


Great!  You all were ready!


You were mostly ready


Don’t wait until the last second


Did you know you had to present?

Content covered thoroughly


Everything was there and now I know about the topic


Missing a concept or two but I’m now better informed


I’m not sure that I learned what I needed to


What content?



Total:  ___ / 15

Written report:

  1. Mechanics
    1. Grammar – 1 point
    2. Spelling – 1 point
    3. Neatness – 1 point
    4. Format: Verdana, Arial, or Times New Roman; 12 pt; Double-spaced; 1” margins – 1 point
    5. Length: One to two pages – 1 point
    6. Header: Student name(s); Title – 1 point
    7. Footer: Date; Page number; School name – 1 point
  2. Material
    1. Doctor’s report

i.      Symptoms – 1 point

ii.      Cause – 1 point

iii.      Treatment – 1 point

iv.      Cure – 1 point

  1. Genetic counselor’s report

i.      Why did this happen? – 2 points

ii.      Will it happen again? – 1 point

iii.      What can be done? – 1 point

  1. Parents’ report

i.      Financial effects – 2 points

ii.      Emotional effects – 1 point

iii.      Social effects – 1 point

  1. Community resources available

i.      For educational needs – 1 point

ii.      For medical progress – 1 point

  1. Conclusions – 2 points
  2. Resources utilized
    1. Quality of resources – 1 point
    2. Quantity of resources – 1 point
  3. Extra credit: Interviews with doctors, nurses, etc. Include:
    1. Name
    2. Time
    3. Date of interview
    4. Content of interview
Chocolate Flavored Cherries

From Dining on DNA: an Exploration of Food Biotechnology by Montana Sate University Extension Service

Modified by Kirstin Bittel and Rachel Hughes


During this lesson students are introduced to the process of recombinant DNA through the imaginary creation of chocolate flavored cherries. Students use a paper simulation to model using restriction enzymes to remove a gene from one plant and insert it into another. Students will be able to identify start and stop sequences in DNA and model using restriction enzyme and ligase to remove sections of DNA and reattach them.

In recombinant DNA, scientists use restriction enzymes to cut DNA into its parts. New genes can be added to sections or specific genes can be removed altogether.


A large candy company has hired your laboratory to conduct an important project. Consumer surveys indicate that people love the combined flavors of chocolate and cherry, so ACME Candy Company is attempting to develop a new product, chocolate flavored cherries. They want to be the first to put these delicious cherries on the market. You are the laboratory technician who has been hired to insert the gene for chocolate flavor into cherry DNA so that it bears a fruit with chocolate flavor. The “big shot” at your lab has already isolated a gene in chocolate that is responsible for its flavor. Your job is to follow the procedures provided in order to insert the gene responsible for chocolate flavor into vector DNA so that the gene can be carried into the cherry.

Background Information on Recombinant DNA

As you know, DNA is the material within a cell that determines what and organism looks like and how it functions. DNA does all of this with the proteins that it codes. Today, scientists are able to insert pieces of “foreign” DNA into an organism’s DNA so that the organism will show a desired characteristic, produce a certain substance, or even not express an undesirable characteristic. This moving of DNA pieces between unrelated organisms is called recombinant DNA technology.

There are many ways to insert a piece of DNA from one organism into the cells of another organism. In recombinant DNA technology, one of the most widely used mechanisms for DNA insertion is the plasmid from Agrobacterium tumefaciens. A plasmid is a circular ring of DNA which is found in some bacteria. The agrobacterium’s plasmid is unique because it has a DNA transforming region. When the bacterium bumps up against another cell, the DNA within the transfer region (T-DNA) “jumps out” of the plasmid and is inserted into the other cell’s chromosome.

As a biotechnologist, you could use your knowledge about this special capability of the T-DNA region of this plasmid in order to transfer desirable genes into plant cells of your choice. So how do you “recombine” DNA using this technology? Once you have found the DNA that contains the characteristics you want, you must isolate or remove this specific DNA section. Restriction enzymes are special molecules that cut the DNA in specific places so that the section you are looking for can be removed. Once the DNA fragment is cut, it needs to be inserted into the vector DNA (the agrobacterium’s plasmid). You must first isolate the plasmid from the Agrobacterium and then expose the plasmid to the restriction enzyme so that a gap in this circular DNA opens to combine with the new piece of DNA.

The restriction enzymes must be selected carefully so that 1) it cuts the DNA fragment (the new piece of DNA) that contains the specific characteristics you want, and 2) it splices the T-DNA out of the plasmid but leaves the genes responsible for the transfer intact! Now you must “recombine” the plasmid with the DNA fragment coding for the specific characteristic you want. Once the plasmid and the new DNA piece are mixed together they must be joined. Ligase is a molecule that helps to join the exposed ends of the plasmid with the new DNA piece. Ligase acts like tape, binding the pieces together. The new plasmid is put back into the agrobacterium and when the bacterium replicates, the new DNA will too.

    1. Define the terms in bold.
    2. Write down, in your own words, the three main steps of recombinant DNA technology.
    3. Discuss as a group and as a whole class the ways that you could remove a section of DNA from one gene and insert it into Plasmid DNA.
      • What would you need to consider before cutting the desired gene out?
      • What would you need to consider before inserting the new gene?
    4. What is your least favorite food? What specific quality about that food do you dislike? What other food could you use to help modify your food?
    5. Write up the laboratory procedures you would use, in detail, to modify your least favorite food. You should begin with extracting the desired trait from the first organism and end with how the “new” gene is recombined into the DNA of your least favorite food.
    6. Removing the desired gene from the linear cacao DNA:
      1. Pick up your restriction enzyme (scissors).
      2. Beginning on the top of your cacao DNA ladder at the end that indicates “start” (the 5’ end) read the bases of the strand until you have read an AGCT sequence all in a row in that order.
      3. Use your restriction enzyme (scissors) to make a cut after the A in the four base sequence.
      4. Continue to make cuts after the A in every four-base AGCT sequence.
      5. Now begin reading the DNA on the bottom strand of your cacao DNA ladder. Start reading from the end that indicates “start” and look for an AGCT sequence all in a row in that order.
      6. As before, make a cut after the A in every four-base AGCT sequence.
      7. One cut on the top cacao DNA strand should be two bases (rungs) away from one cut on the bottom cacao DNA strand. Cut through the hydrogen bonds right down the middle of the DNA ladder in order to connect the two closest cuts.
      8. Repeat this step on the opposite end of the DNA ladder. You should make a total of two cuts down the middle of the ladder, right through the hydrogen bonds.
      9. Remove the strip of DNA that comes out of the DNA ladder. This piece of DNA should have two exposed rungs and a central portion of the ladder intact. It contains the chocolate-flavor gene.
      10. Put this DNA aside for the moment and move on to the plasmid.
    7. Getting the plasmid ready for insertion of the gene
      1. Cut your circular plasmid out so that it looks like a large doughnut ring (make sure the middle of the doughnut ring is cut out).
      2. Each of the two strands of the circular plasmid is to be read in a certain direction as indicated by the arrows on the plasmid.
      3. Beginning on the outside at the arrow, start reading along the plasmid in the direction of the arrow until you come across an AGCT sequence all in a row.
      4. With your restriction enzyme (scissors), make a shallow cut (only to the middle of the ring) after the A in every AGCT sequence.
      5. Now going in the opposite direction read along the inside loop of the plasmid, reading until you come across the AGCT sequence on the inside DNA strand.
      6. With your restriction enzyme, make a shallow cut after the A in every AGCT sequence.
      7. Once again, each cut on the inside loop should be two rungs (bases G, C) away from a cut on the outside loop.
      8. Cut through the hydrogen bonds right down the middle of the plasmid loop in order to connect each of the two closest cuts.
      9. With the final cut, open the loop and look closely at the two exposed rungs.
    8. Insertion of the New Gene into the Plasmid (Recombination)
      1. Look at the strip of DNA that you removed from the cacao DNA.
      2. Compare this strip with the cut-open plasmid DNA.
      3. Can you see how they match together? The two pieces of DNA fit together like a puzzle.
      4. Match the shapes as well as the bases (A goes with T and C goes with G).
      5. Take out your ligase (tape) and insert the cacao DNA into the plasmid loop.
      6. You just inserted the cacao gene for chocolate flavor into the plasmid, and now the plasmid can be used to carry the cacao chocolate-flavor gene into the cherry plant!
    9. How can we use our knowledge of DNA to make specific foods taste better?
    10. How can this technology be applied to other areas?
Dihybrid Cross With Corn


A dihybrid cross is a cross between individuals that involves two pairs of contrasting traits. Predicting the results of a dihybrid cross is more complicated than predicting the results of a monohybrid cross. All possible combinations of the four alleles from each parent must be considered. We will examine a dihybrid cross involving both color and texture. Purple (P), is dominant to yellow (p), and smooth texture (S) is dominant to wrinkled (s). Both parent plants are heterozygous for both traits.


Appropriate ear of corn.


First let us use a Punnett square to examine the theoretical outcome of the Heterozygous X Heterozygous dihybrid cross.

  1. Fill in the Punnett square. Each box represents a genotype possibility for an offspring. Place the alleles donated by each parent in the corresponding box. One offspring has been done for you as an example. Now list the possible phenotypes in the spaces below the Punnett square. REMEMBER: a phenotype is how the offspring will look. If an individual’s genotype is heterozygous, the dominant trait will be expressed in the phenotype. There are four possible phenotypes for the offspring of this cross, and both traits are in each phenotype. One has been done for you as an example.
  2. Now show the ratio of the phenotypes. For this, it is simply the number of possible individuals with each phenotype.
  3. Actual cross: Now we will make a count of an actual cross and compare the calculations of it’s phenotype ratios to the theoretical.
  4. Obtain an ear of corn that is the result of a cross that was Heterozygous X Heterozygous for both traits. Copy the four phenotypes in the appropriate blanks, then count and record the number of kernels for each phenotype.
  5. Now calculate the ratio for the cross. The phenotype with the least number of individuals you will call 1. Place the 1 in the space below the appropriate phenotype. Now divide the other count numbers by the number of individuals from the phenotype you called 1, and round your answers to the nearest whole number. Put the answers under the appropriate phenotypes.
  6. Compare your results with the theoretical answers you obtained for the cross. Did you obtain a ratio in your experiment that was close to the theoretical?
Phenotype: _____________ _____________ _____________ _____________
Number: _______ _______ _______ _______
Ratio: ______ : ______ : ______ : ______

Polygenetic Traits Lab


This activity will demonstrate how polygenic traits work and why certain traits in a population can be graphically represented by a bell curve.

Materials:   6 pennies


  1. Each “couple” (lab partners)  will carefully flip all six coins.
  2. Record the number of heads and tails that result from the flip in Table 1.
  3. Continue to flip the coins and continue to record the number of heads and tails that result from the flip until the data Table 1 is completed.

Table 1.- Group Results

Flip (group) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
  1. Complete table 2 by adding up the number of times the following situations occurred.

Table 2.- Group and class results

Flip Situation 0 Tails
6 Heads
1 Tails
5 Heads
2 Tails
4 Heads
3 Tails
3 Heads
4 Tails
2 Heads
5 Tails
1 Heads
6 Tails
0 Heads
Group total
Class total
  1. Record your results from Table 2 in the computer with the class results.
  2. Graph your group’s results in the bar graph below:
0 tails
6 heads
1 tail
5 heads
2 tails
4 heads
3 tails
3 heads
4 tails
2 heads
5 tails
1 head
6 tails
0 heads
  1. Record the class results in Table 2.
  2. Construct a bar graph from the class data on the graph paper included with this packet.  The number of heads and tails will go on the X axis while the number of times that the situations occurred will go on the Y axis.
0 tails
6 heads
1 tail
5 heads
2 tails
4 heads
3 tails
3 heads
4 tails
2 heads
5 tails
1 head
6 tails
0 heads


Use the following height table to answer the questions on the next page

Penny Situation Height
0 Tails and 6 Heads ~ 6 feet 6 inches
1 Tails and 5 Heads ~ 6 feet 3 inches
2 Tails and 4 Heads ~ 6 feet 0 inches
3 Tails and 3 Heads ~ 5 feet 9 inches
4 Tails and 2 Heads ~ 5 feet 6 inches
5 Tails and 1 Heads ~ 5 feet 3 inches
6 Tails and 0 Heads ~ 5 feet 0 inches

Remember: Heads are dominant genes that have an effect of making one taller.  Tails are recessive and have a shortening effect.

  1. Parents give (All or Half) of their genetic material to their children.

Example for the rest of the questions:  A man is 5 feet 9 inches tall, has 3 heads (dominant genes) and 3 tails (recessive genes).  He will give 3 genes to his child.  These 3 genes will be given randomly.  The following are the possible genes for sperm:

  • He can give 3 dominant genes (heads) and 0 recessive genes (tails).
  • He can give 2 dominant genes (heads) and 1 recessive gene (tails).
  • He can give 1 dominant gene (heads) and 2 recessive genes (tails).
  • He can give 0 dominant genes (heads) and 3 recessive genes (tails).

These are all the possible combinations that he can give his child.  The height of the mother will dictate the genes that she will give to the child.  The combination of the mother’s genes and the father’s genes will decide the height of the child.

  1. If a male is 5 feet 6 inches tall, it means that he has 4 recessive genes and 2 dominant.  He will only give 3 genes to his child.  What are the possible combinations of genes that he can give?
  • He can give ______ dominant and _______ recessive.
  • He can give ______ dominant and _______ recessive.
  • He can give ______ dominant and _______ recessive.
  1. The male is 5 feet 9 inches and the female is 5 feet 6 inches.  Is it possible for them to give their child the necessary genes so the child can be 6 feet 6 inches tall? Explain your answer. What is the maximum height possible for their child? _____  Minimum height?______
  2. If 2 parents are 6 feet tall, is it possible to have a child that is 6 feet 6 inches tall? Explain. What is the maximum height for the children?______ Minimum height?_______
  3. If the parents are both 5 feet 6 inches tall, what are the maximum and minimum heights possible for the children? Maximum___________ Minimum___________
  4. If the male is 6 feet 3 inches tall and the female is 5 feet tall, what are the maximum and minimum height possible for the children? Maximum__________ Minimum_________
  5. List 3 other polygenic human traits:
  6. How are polygenic traits different in their expression (what you see) than traits that only require 2 genes?
Genetics of Pill Bugs


The pill bug (woodlice, rolly-polly, or potato bug; scientific name Armadillidium vulgare) is very common to find in the soil, underneath logs, and hidden under leaves. Since they are so common, it’s easy to overlook that they actually have many different colors: green, brown, grey, cream, orange and red. If you count the numbers of pill bugs that represent each color, it’s possible to determine which colors are genetically dominant and which colors are genetically recessive and how these might be related.
Birds, amphibians, and reptiles eat pill bugs. In fact, they are food for almost everything that finds it. Why would the pill bug have such a wide variety of colors?
Remember, dominant traits are traits that are always seen when the organism has it; you only see recessive traits when an organism has two copies of that trait in its DNA. Why would some traits be dominant and some be recessive?


  • Hand Lens
  • 50 pill bugs
  • Pencil
  • Paper
  • 6 containers


  1. Sort the pill bugs into the containers by color, maintaining a tally for each bug that you place into the correct container.
  2. Calculate the percentage of each color bug that you found (if you have 50 total bugs, it’s easy: multiply each number by 2).
  3. Create a data table with the following columns: Color, number, and percentage. Include your group’s data.
  4. Create a second data table with the same columns, but include the class data.
  5. Replace the pill bugs into the habitat!


  1. Answer the questions from the background.
  2. Which would you suppose is the dominant trait(s)?
  3. Which would you suppose is the recessive trait(s)?
  4. What would happen if you crossed pill bugs that both had recessive traits?
How Are Dimples Inherited?
  1. Write the last 4 digits of your telephone number.  These 4 random digits represent the alleles of a gene that determines whether a person will have dimples.  Odd digits represent the allele for the dominant trait of dimples.  Even digits stand for the allele for the recessive trait of no dimples.
  2. Use the first 2 digits to represent a certain father’s genotype.  Use the symbols “D” and “d” to write this genotype, as shown in the example.
  3. Use the last 2 digits the same way to find the mother’s genotype.  Write her genotype using “D” and “d”.
  4. Use the Punnett Square at the bottom of this lab as an example to construct a Punnett square for the cross of these parents.  Then, using the Punnett square, determine the probability that their child will have dimples.

Analyze and Conclude:

  1. What percentage of the children will be homozygous dominant (DD)?
  2. What percentage of the children will be heterozygous dominant (Dd)?
  3. What percentage of the children will be homozygous recessive (dd)?
  4. What percentage of the children will be expected to have dimples if one parent is homozygous for dimples if one parent is homozygous for dimples (DD) and the other is heterozygous (Dd)?

Punnett Square




TT  25%

Tt  25%


Tt  25%

Tt  25%