Students explore concepts of heredity in beef cattle and identify dominant and recessive traits. Grades 3-5

allele: a variant of a gene

Angus: a Scottish breed of beef cattle known for their good meat quality

dominant: a trait that can be expressed only when two copies of the gene is present

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

genotype: the genetic makeup of an organism

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

Hereford: an English breed of beef cattle with a red body and white face and stomach

heterogeneous: trait produced by two different genes or a combination of genes

homogeneous: trait produced by two identical genes

inherited: derive a quality or characteristic genetically from one's parent or ancestors

inherited trait: a genetically determined characteristic or quality that distinguishes someone or something; inherited traits are passed in DNA from parents to their offspring

linked genes: genes that are inherited together or do not assort independently

phenotype: the set of observable characteristics of an organism resulting from the interaction of its genotype with the environment

recessive: a trait that can be expressed only when two copies of the gene is present

The study of genetics and heredity are incredibly important to agriculturalists. Heredity is the passing of physical or mental characteristics genetically from one generation to another. For centuries, farmers and ranchers have selected plant varieties and livestock for specific genetically determined characteristics called traits. Livestock producers select for animals with increased milk production, ample muscle mass, or structural correctness, among other things. Selecting for these traits allows farmers to produce a higher quality and more abundant food supply.

Most plants and animals have two of every kind of gene, a unit of heredity transferred from a parent to the offspring. One comes from their mother, and one comes from their father. Only one gene from each parent is passed to each offspring for a particular trait. Linked genes are inherited together or do not assort independently. There are different forms of a gene that are referred to as alleles. Alleles are forms of the same gene with small differences in their DNA sequence. These small differences contribute to each organism's unique physical features and are called phenotypes. A plant or animal's genotype refers to the genetic makeup inherited by the offspring's parent.

Alleles can be either dominant or recessive. Dominant alleles overpower recessive alleles and are always expressed in offspring. Recessive alleles are only expressed if a recessive allele is inherited from both parents, because they are overpowered by even one dominant allele. For example, the allele in cattle that causes horns to grow is recessive. The hornless, or polled, allele is dominant, so more cattle are polled than horned. Dominant alleles are denoted by an uppercase letter, and recessive alleles are denoted by a lower case letter. When the combination of both dominant and recessive genes are present (one parent contributed a dominant gene and one contributed a recessive gene), the condition is called heterozygous. When both genes are either dominant or recessive the condition is called homozygous. Heterozygous would look like "Aa," and the homozygous condition would be expressed as "aa" representing the recessive trait or "AA" representing the dominant trait.

Understanding genetics is crucial for farmers. Beef producers try to select and perpetuate characteristics in their cattle such as good marbling (intramuscular fat that contributes tenderness, juiciness and flavor), abundant muscle mass, and structural correctness. With an understanding of the science of genetic inheritance, beef producers can also select for other phenotypic characteristic such as the natural presence or absence of horns. Cattle who naturally do not have horns are called polled cattle. The polled gene (P) is dominant to the horned gene (p). Through selective breeding, cattle ranchers can select breeding stock that will produce calves without horns to eliminate the need to dehorn cattle for safety and management purposes.

There are numerous breeds of beef cattle in the United States and throughout the world. Each breed has distinguishing characteristics that can be passed to their offspring.  Angus cattle are polled (naturally without horns) and either all red or all black in color with black being the dominant color. They are used widely in crossbreeding programs to improve carcass (meat) quality, milking ability, and to eliminate horns using genetics. Hereford cattle are reddish brown with a white face and underbelly. They are larger framed with abundant muscle but can have less marbling than Angus cattle. Herefords can be either polled or horned. Angus and Hereford cattle are often used in crossbreeding programs in hopes of maximizing hybrid vigor. A Black Angus/Hereford cross can be identified by a white face and all black body, usually with no horns. They are typically known as a "Black Baldy." These crossbred calves are normally a product of an Angus cow bred with a Hereford bull or vice versa. Crossbred cattle have been shown to have up to 20% more lifetime productivity over purebreds, which leads to an economic advantage for farmers.

1. Begin a discussion with students by asking the following questions:
   • Does chocolate milk come from a brown cow? If it doesn't, why not? (Coat color doesn't reflect the color of milk. If we want chocolate milk, we have to add chocolate flavored powder or syrup to the milk.) Explain that most of the characteristics of cattle (including coat color) are inherited from their dam (mother) and sire (father). 
   • How are beef cattle different from dairy cattle?
   • What are some characteristics of humans that are inherited? Do all humans have identical inherited traits? How are they different or the same?
   • What are some characteristics in cattle that can be inherited? Do beef cattle and dairy cattle have the same or different inherited traits?
   • Why is inheritance important to a cattle rancher?

Activity 1: Beef Cattle K-W-L Chart

1. Begin by passing around a post-it note or small piece of paper to every student. Ask the students to close their eyes. Have them visualize their response to the following question: "What comes to mind when I say the words beef cattle?"
2. Have students jot down what came to their mind on the post-it note. Clarify to students that they can draw a picture or write down a word or phrase that came to their mind.
3. Next, have students place their post-it note into a bucket. Remove the post-it notes one by one and begin to add the student's responses to the K section of a KWL chart drawn on chart paper or the board. These responses reflect what the students Know about beef cattle. Discuss responses as they are revealed.
4. After the K section is completed, ask students what they would like to learn about beef cattle. Add their responses to the W section of the KWL chart. These responses will represent what the students want to learn about beef cattle.
5. Introduce the digital version of My Family's Beef Farm by Katie Olthoff to the class. Read the book aloud to the students, emphasizing the physical characteristics of the beef cattle.
6. Follow the same idea above and have students write on a second post-it note what they Learned about beef cattle from the book. Add these responses to the L section of the KWL chart.
7. Compare the W and L sections of the KWL chart to see if the students learned all they wanted to.
8. Next, determine any questions in the W section that were not answered by reading My Family's Beef Farm. Place students in small groups based on the number of sticky notes that still need to be researched.
9. Assign each group one sticky note from the W section that still needs to be researched and explored.
10. Provide students an opportunity to research more information about beef cattle by using the Ag Facts section of the lesson plan, searching on Google, and/or providing a copy of the Beef Ag Mag to the students.
11. Once each group has gathered the information needed to answer their question from the W section of the KWL chart, have them add it to a post-it note, share it with the class, and then place the post-it note in the L section of the KWL chart.

Activity 2: Build-a-Calf

1. Divide students into groups of four students or less. Give each student a Build-a-Calf activity sheet and each group a coin.
2. Instruct students to read the instructions and then play the game.
   • The students should flip the coin to determine if the dominant or recessive allele is being passed on from the dam (female) to the offspring. If the coin lands heads up, the dominant gene is passed on. If the coin lands heads down, the recessive gene is passed on. The students should record the gene on their activity sheet and then flip the coin again to see if the dominant or recessive allele is being passed on from the sire (male). Once they have determined the allele from each parent, they should select the correct homozygous or heterozygous pairing on the activity sheet which will tell them which phenotype will be inherited. 
   • Repeat this process for all of the traits represented.
   • Have the students color the calf on the back side of their activity sheet to reflect the genes passed on from the parents to the offspring.
   • Have the students compare their offspring to the Breed Pictures. Does their calf look more like an Angus or a Hereford? Does it look like a cross? What genes determined that?
   • In their groups, have the students calculate the percent of animals that look like Herefords, Angus, or crossbreds. Is there an even number of each? Why or why not?
3. As a group, have students discuss:
   • Are beef producers the only farmers that need to be concerned with genetics? Are there traits in crops or other livestock that are affected by heredity? What might some of those traits be?
   • If an animal lives in an arid desert, what traits might you select? What might help your animal be more successful in that environment?
   • Do the traits in the game directly affect the animal's use for consumers? What are some traits that might directly affect the animal's use for consumers? Is there a way to select for traits that would focus on nutrition or healthfulness?

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

• Beef cattle are raised on family farms that provide a balanced feed ration, fresh water, and pastures for grazing the herd.
• Genetics play an important role for beef farms in selecting cattle with specific traits to produce a higher quality product for consumers and to increase food production.
• Different breeds of cattle have distinguishing characteristics that can be transferred to their offspring. This is known as heredity.
• Crossbred cattle provide more desirable traits and lifetime productivity over purebred cattle.

1. http://pubs.ext.vt.edu/400/400-803/400-803.html
2. https://beef2live.com/story-ranking-states-beef-cows-0-108181
3. https://www.beefitswhatsfordinner.com/
4. http://www.selectsires.com/index.html?version=20170404

Adapted from Oklahoma Agriculture in the Classroom

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