Hands-on Activity Heredity Mix 'n Match

Learning Objectives

After this activity, students should be able to:

• Distinguish between genotypes and phenotypes.
• Determine the genotypes and phenotypes of offspring that could result from a given pair of parental genotypes.
• Describe why children are neither genetically nor phenotypically identical to their parents.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

For a class of 30 students, you need:

• 38 brown paper lunch bags
• 100 sturdy toothpicks (plastic cocktail-type ones work especially well)
• about 80 red jelly beans and 70 pink jelly beans to represent tongue rolling alleles (other types of candy, such as gum drops and/or miniature marshmallows may be substituted, and other color combinations may be used for this and the next three items)
• about 100 purple jelly beans and 50 white jelly beans to represent eyelash length alleles
• about 90 black jelly beans and 60 blue jelly beans to represent eye color alleles
• about 80 orange jelly beans and 70 yellow jelly beans to represent ear lobe attachment alleles
• 15 sheets of construction paper
• transparent tape
• (optional) photocopied pictures of George W. Bush or Michael Jordan, and Tom Cruise or Matt Damon, that clearly demonstrate attached earlobes (Cruise and Damon) and detached earlobes (Bush and Jordan); these can be obtained by conducting a Internet search using the Google image option

Worksheets and Attachments

Pre-Req Knowledge

From the associated lesson, students should have an understanding:

• of dominant and recessive alleles
• of chromosomes
• that genes come in pairs, one set contributed by the mother, and a corresponding set contributed by the father

Students should also be able to determine the probabilities for outcomes of simple events, such as the results of two coin tosses

Introduction/Motivation

Tell students that they will attempt to answer the question, "Why don't we look just like our same-sex parents?" Explain that to do this, they will investigate the inheritance of four human physical characteristics, called traits, for short. One is already familiar to them. It is the tongue rolling trait, and they know that it comes in both dominant and recessive alleles. The second trait they will use in their experiment is the eyelash length trait. It also comes in dominant and recessive forms, with the long lash allele being dominant and the short lash length being recessive. The third trait is the eye color trait, with brown eye color being dominant over blue eye color.

The last trait is the earlobe attachment trait. If the lower ear lobe hangs free of the side of the face and can be flicked back and forth, the earlobe is detached. The detached earlobe allelle is a dominant allele. George W. Bush and basketball player Michael Jordan both have detached earlobes. Attached earlobes, however, do not hang free. Instead, the bottom of the earlobe curves right into the side of the face. Actors Tom Cruise and Matt Damon have attached earlobes. If possible, show the class pictures of these well-known people as examples

Then, briefly explain the differences between genotype and phenotype. Explain that genotype is a shorthand way to describe the pair of alleles a person has for a particular trait. We choose a letter of the alphabet to represent the dominant trait, and we write it in uppercase to show that it is the dominant form. The lowercase letter represents the recessive form. For example, the genotype of a person who inherited the dominant alleles for tongue rolling from both parents would be written as "RR." The genotype of a person who inherited the recessive alleles for tongue rolling from both parents would be "rr." The genotype of a person who inherited a dominant allele from one parent and a recessive allele from the other parent would be "Rr." Point out that in cases like this last one, the capitalized letter is always written first.

In contrast, a phenotype is a description of the physical trait that results from the combination of alleles in the genotype. Thus, anyone with the RR or Rr genotype has the tongue rolling phenotype. Anyone with the rr genotype, however, has the non-tongue rolling phenotype.

Give each student a copy of the Genotypes and Phenotypes Worksheet. This will provide a little practice in using these terms and writing genotypes for the traits that will be used in the activity.

Procedure

1. Sort the students in pairs.
2. Have Partner 1 choose jelly beans that represent a pair of alleles for each of the four traits. Have Partner 2 do the same.
3. Student pairs record their genotypes and phenotypes.
4. One at a time for each of the traits, Partner 1s place their jelly beans in a lunch bag and without looking, choose one to "give" to their baby. Partner 2s should do the same. These are made into toothpick chromosomes for their baby.
5. The "parents" then obtain additional jelly beans and construct their own chromosomes, based on the genotypes recorded in step 3.
6. Students make observations of similarities and differences in genotypes and phenotypes parents and offspring.
7. Students determine theoretical probabilities for phenotypes of offspring, given parental genotypes.

Body of Activity

Tell students that they are going to do an experiment to see how babies inherit different traits. Before they can make a baby, however, they must form pairs. Realistically, one partner would be male and the other would be female but to avoid any gender issues occurring, the gender of pairs is not essential.

Give each student a toothpick. Explain that these will be used to create chromosomes for their babies. Each parent will contribute one chromosome to his or her baby, which is similar to what happens in real life. These chromosomes, however, will contain only four genes, instead of the hundreds that would be on a real chromosome. The four genes on the toothpick chromosomes be alleles for each of the four traits mentioned earlier. The alleles are represented by candies of different colors.

Next, explain the color code the class will use, and either write the color code on the board, or have it written on a cards for each pair of students to use as they work. For example, for the colors suggested in the Materials List, write:

Then explain that each student must determine his or her own genotype and phenotype for these four traits. They do this by choosing, without looking, two jelly beans from a paper bag containing a mixture of red and pink jelly beans, two from a different bag containing a mixture of purple and white jelly beans, etc. Prepare these bags in advance by mixing all the red and pink jelly beans together and then dividing the mixture among two bags. Having two bags available, one for boys to choose from and one for girls, will make the selection process a little easier than if all the red and pink jelly beans were in one bag for the whole class. Do the same for the other three color combinations, and be sure to label the bags as: tongues, lashes, eyes and earlobes.

Once all students have returned to their work spaces with eight jelly beans each, provide each student with a paper bag and the Heredity Mix 'n Match Procedure Handout.

When all of the student pairs have completed the exercise in the handout, ask them to complete the follow-up questions in the Any Matches? Questions Handout.

End the activity by discussing their responses to these questions, and also using the Investigating Questions for further discussion.

Vocabulary/Definitions

allele: One form of a gene that can occur in two or more forms; for example, three different alleles code for a protein found on the surface of red blood cells, giving rise to the A, B, and O blood types.

dominant: A visible or otherwise observable gene for a trait that can mask a recessive form of the same gene.

hemoglobin: The iron-containing protein found in red blood cells that carries oxygen.

meiosis: A type of cell division in which one cell undergoes two divisions, resulting in four new cells, each containing half the amount of genetic material that was in the original cell. Meiosis is an example of sexual reproduction.

mitosis: A type of cell division in which one cell divides into two new cells, each genetically identical to the original cell. Mitosis is a form of asexual reproduction.

recessive: A gene for a trait that can be masked or hidden by a dominant form of the same gene.

Assessment

In a quiz or writing assignment, ask students to:

• Explain the difference between a genotype and a phenotype, and give an example.
• Determine the different genotypes and phenotypes of offspring that could result from a given pair of parental genotypes.
• Describe why children are neither genetically nor phenotypically identical to their parents.

Investigating Questions

• What type of reproduction did we model with this activity? (sexual or asexual)
• Sexual reproduction results in a new offspring with a combination of genes from both parents. When might an organism need to regenerate cells asexually, yielding new cells identical to existing cells?
• How would the jellybean model be different if you were simulating asexual reproduction?
• How do you think your answers to questions 1-6 of the Any Matches? Questions Handout would change, if you had done the exercise using six traits instead of four? Why do you think that?
• How do you think your answers to questions 1-6 would change if you had used 10 traits? Or 100?
• No one yet knows exactly how many genes are carried on human chromosomes, but estimates range from 100,000 to 200,000. How likely do you think it is that a baby would be genetically identical to either of its parents?
• Why might it be a good idea for children to not be genetically identical to either of their parents?

Safety Issues

• Watch that students do not poke each other with the toothpicks.
• Advise students to take care when using force to push the candy onto the toothpicks. If the toothpicks are bent during this process, they could snap and cut skin.
• If you are going to allow students to eat the candy when they are done, make sure all work surfaces are clean and students have washed their hands thoroughly before beginning the activity.

Activity Extensions

Explain what the sex chromosomes are and let the "fathers" in the class toss a coin to determine the sex of their babies. (Some pairs may need to rename their babies after doing this!)

Assign small student groups to research other topics in genetics and inheritance. One group could find out what the difference is between identical and fraternal twins, and what causes them. Other groups could find out what some genetic disorders or diseases are, and what causes them. Down's syndrome, cystic fibrosis and Huntington's disease are all easy to understand. A little more challenging are red-green color blindness (the trait is carried only on the X chromosomes), and sickle cell disease (neither allele is dominant, so individuals that are heterozygous have both normal and sickled red blood cells).

Copyright

Contributors

Supporting Program

Acknowledgements

This content was developed by the MUSIC (Math Understanding through Science Integrated with Curriculum) Program in the Pratt School of Engineering at Duke University under National Science Foundation GK-12 grant no. DGE 0338262. However, these contents do not necessarily represent the policies of the NSF, and you should not assume endorsement by the federal government.