Students explore how genes affect important traits such as growth, reproduction, disease resistance, and behavior and discover the responsibilities of an animal geneticist. Grades 3-5

gene: a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring

heredity: the passing of traits from a parent to its offspring

offspring: the child or young of two parents

trait: observable, physical characteristic obtained through genetic inheritance

This lesson is one in a series of five related lessons to promote the development of STEM abilities and critical thinking skills, while fostering an appreciation for the people involved in livestock production. For more information about what STEM is, why it's important, and how it can be implemented in your classroom, watch the video, What is STEM? The curriculum includes real-life challenges for students to investigate, inquiry-based labs, and opportunities to plan and construct models. Featured careers include:

• Animal Physiologist: Significant Surroundings
• Agricultural Engineer: Build it Better
• Animal Geneticist: Roll of the Genes
• Animal Nutritionist: Got Guts?
• Range Manager: Homes on the Range

Heredity is the passing on of traits from parents to offspring. Most plants and animals have two of every kind of gene, one from their mother and one from their father. Only one gene from each parent is passed to each offspring for a particular trait. For example, a gene will determine eye color. Alleles are forms of the same gene with small differences in their DNA sequence. For example, one allele will determine brown eye color and another allele will determine blue eye color. These small differences contribute to each organism’s unique physical features. These physical features are called “phenotypes.”

Some alleles are dominant while others are recessive. Dominant alleles overpower recessive alleles and are always expressed in offspring. Recessive alleles can only be expressed in offspring if both parents contribute a recessive allele. One of the easiest ways to calculate the mathematical probability of inheriting a specific trait was invented by an early 20th century English geneticist named Reginald Punnett. His technique employs what we now call a Punnett square. This is a simple graphical way of discovering all of the potential combinations of two gene sets and the resulting genetic traits. It also illustrates the probability, or chances, of each combination occurring.

Understanding and being able to use a Punnett square is a basic skill for an animal geneticist. They use the Punnett square to predict the outcome of breeding two animals. By understanding how genes are passed on to offspring, scientists can help improve a wide range of economically important traits. They can also decrease the likelihood of an animal receiving an undesirable trait which may affect the health and well-being of the animal.

In this lesson, students will use a simple Punnett square to predict the outcome of fictional and fantastical livestock breeding experiments. They will practice determining the probability of each possible outcome and create a drawing of the offspring they create.

Refer to the Answers to Commonly Asked Questions for more background information.

1. Brainstorm physical features, such as eye color and hair, which make students look different from each other.
2. Explain that these characteristics are called traits. A trait is a physical characteristic or feature, obvious and observable, which is inherited from one or more parent.
3. Ask the students if animals also possess traits. Brainstorm physical characteristics found in animals. Examples could include coat color or pattern, size of the animal, the presence or absence of horns, etc. 
4. Explain that like people, animals also have specific traits that distinguish them. These traits are a result of their genetic makeup. At the completion of this lesson, students will:
   • consider how genes affect traits; and
   • discover the role of an animal geneticist.

1. Review the concept of probability and related terms such as chance, likely, unlikely, possible, and impossible with the students.
2. Instruct the students to raise their hand if they’ve ever been told they look like a family member. Allow a few students to share about their personal experience. Explain that traits are passed from parents to their children through DNA. The piece of DNA that carries the trait is called a gene. Clarify that traits may be dominant or recessive. A dominant trait is displayed if one or both parents carry the trait. A recessive trait is displayed only when both parents carry the trait.
3. Tell the students that traits are also passed on in the animal world. For example, livestock geneticists have been able to improve a breed’s traits through selective breeding programs. For example, breeders were able to cross Brahman beef cattle (show students the Brahman Beef Cattle photograph) and Angus beef cattle (show students Angus Beef Cattle photograph). Have students describe some of the obvious physical traits of each breed. Explain that the breed created from the two breeds is called a “Brangus” (show students the Brangus Beef Cattle photograph). Encourage students to identify the physical traits inherited from the Brahman and the Angus breeds. Explain that geneticists purposefully developed the breed to create a superior animal. Brahman cattle are tolerant to hot climates, and outstanding mothers. Angus cattle have excellent meat quality. The Brangus has the characteristics of both breeds.
4. Distribute the Have You Any Wool? handout to students and project a copy onto a large screen. Read the sheep’s genetic background aloud and define any unknown scientific terms. Explain that the Punnett square is a diagram that helps geneticists predict the outcome of breeding two animals.
5. Explain that the class is going to use the Punnett square to determine what color wool the sheep’s offspring will have. Dominant traits are expressed with a capital letter and recessive traits are expressed with a lowercase letter. If dominant and recessive traits are combined, the dominant trait will always overpower the recessive trait. Complete the Punnett square in front of the class while explaining the process.
6. Remind the students that probability is the likelihood that a particular event, or outcome, will occur. It is expressed as a fraction with the numerator being the total number of favorable outcomes and the denominator being the total number of possible outcomes. In this scenario, two quadrants have dominant genes for white wool and two quadrants have recessive genes for black wool; thus the lamb has a 2 out of 4 chance of inheriting white wool and a 2 out of 4 chance of inheriting black wool. Have every student roll a die to determine the breeding outcome. Instruct students to sketch a portrait of the lamb in the box provided at the bottom of the handout.
7. Tell the students that now that they know how to use the Punnett square to predict what animals will look like, they will practice being an animal geneticist by creating their own breed of cattle. Distribute the Cattle Call handout to students. Students will use the information provided about the bull and cow to determine the physical attributes of their offspring. Explain that the traits used as examples are not necessarily real cattle traits, but the traits will help students understand the main concepts of heredity. Instruct students to complete the Cattle Call handout. Review the handout and allow students to share their artwork.

Variations

• Introduce genetics through an educational video on heredity. Check out the video “Heredity” on BrainPOP or search YouTube using the term “Punnett Square.”
• Students work on the project individually, with a partner, in small groups, or as a class.
• Students research actual phenotypes expressed in breeds of cattle. They create new variations of cattle by crossing actual breeds with the imaginary cattle featured in the Cattle Call handout.

ELL Adaptations

• While leading students through the Have You Any Wool? handout, allow students time to think and respond to questions.
• Throughout the lesson ELL students can be partnered with students that are proficient or advanced English speakers.
• Students can define new terms like genes and alleles in their science journal or on a classroom word wall for future reference.

After conducting these activities, review and summarize the following key concepts:

• An animal geneticist studies the genetic makeup of animals. They can help farmers and ranchers select and promote desirable traits in their animals. As animals improve, they are better able to provide meat, milk, and eggs to our diet.
• The Punnett square is a tool used to predict the likelihood of an animal inheriting a specific trait.
• The work of an animal geneticist benefits both producers (farmers and ranchers) and consumers.

1. http://www.sciencekids.co.nz/sciencefacts/careers/geneticist.html
2. http://learn.org/directory/category/Biological_Sciences/Genetic_Sciences/Animal_Genetics.html

This lesson was funded in 2012 by the United States Department of Agriculture’s National Institute of Food and Agriculture through the Secondary Education, Two-Year Postsecondary Education, and Agriculture in the K-12 Classroom Challenge Grants Program (SPECA). Graphics submitted by California Foundation for Agriculture in the Classroom.

Executive Director: Judy Culbertson
Illustrator: Erik Davison
Layout and Design: Nina Danner

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