Build a Calf

Build a Calf

Target Grade Level / Age Range:

Grades 3-5

Time:

45 minutes

Purpose:

Students will explore genes and heredity in the context of beef cattle.

Materials:

 

Suggested Companion Resources

  • Little Joe by Sandra Neil Wallace

Vocabulary

  • Trait – a genetically determined characteristic
  • Gene – a unit of heredity that is transferred from a parent to offspring and is held to determine some characteristic of the offspring.
  • Inherit – derive a quality or characteristic genetically from one’s parent or ancestors
  • Heredity – the passing on of physical or mental characteristics genetically from one generation to another.
  • Dominant – A trait that can be expressed when just one copy of the gene is present
  • Recessive – A trait that can be expressed only when two copies of the gene is present
  • Hereford – an English breed of beef cattle with a red body and white face and stomach
  • Angus – A Scottish breed of beef cattle known for their good meat quality
  • Linked genes – genes that are inherited together or do not assort independently
  • Phenotype – physical features of an animal

Interest Approach or Motivator

Ask students: “Does chocolate milk come from a brown cow?” If it doesn’t, why not? Because genetically, coat color doesn’t reflect body color (or the color of milk). Most of the characteristics of cattle are inherited from their dam and sire, but if we want chocolate milk, we have to add chocolate. What are some characteristics of humans that are inherited? What do you think some characteristics of cattle that can be inherited might be? Why does that matter?

Background – Agricultural Connections

The study of genetics and heredity are incredibly important to agriculturalists. For centuries, farmers and ranchers have selected plant varieties and livestock for specific beneficial 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. 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. 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, which are called “phenotypes.”

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 both dominant and recessive genes are present (one parent contributed a dominant gene and one contributed a recessive gene), the condition is called “heterozygous.” This would look like an “Aa.” When both genes are either dominant or recessive, the condition is called “homozygous.” This would look like “aa” or “AA.”

Understanding genetics is crucial for farmers. Beef producers try to breed for good characteristics, such as good marbling (intramuscular fat that contributes tenderness, juiciness and flavor), abundant muscle mass, and structural correctness. Beef producers try not to breed cattle to have horns, because they can be dangerous, be small bodied, or have bad temperament. Breeders also have to pay attention to any genetic diseases that may be passed on from dams and sires to offspring.

There are several beef breeds that have distinguishing characteristics that are transferrable to their offspring. Angus cattle are generally smaller bodied, less muscular cattle with good marbling and poor disposition. They are polled and either all red or all black. Hereford cattle are reddish brown, with a white face and underbelly. They are larger framed with abundant muscle, but have less marbling than Angus cattle. Herefords can be either polled or horned, and have calm dispositions. Angus and Hereford cattle are often bred together to get the best of both worlds: a large bodied, heavily muscled animal with good meat characteristics. A Black Angus-Hereford cross can be identified by a white face and all black body, usually with no horns, which is usually called a Black Baldy. These are usually a product of an Angus cow bred with a Hereford bull. Crossbred cattle have been shown to have up to 20% more lifetime productivity over purebreds, which leads to an economic advantage for farmers.

Procedures

  1. Prepare materials: each group will need a game set, including a dice or coin, instructions sheet, breed pictures, and a copy of the genes worksheet and calf color page for each group member.
  2. Break students up into the desired groups. A group should not have more than four students. Pass out materials to students.
  3. Have the students read the instructions to themselves, and then work in groups to play the game.
    1. Students should roll the dice or flip the coin to determine if the dominant or recessive allele is being passed on from the dam. If the coin lands heads up, the dominant gene is passed on. If the coin lands heads down, the recessive gene is passed on. Students should record the gene that they rolled on their gene worksheet, and then roll again to see if the dominant or recessive allele is being passed on from the sire. Once they have determined the allele from each parent, they should select the correct homozygous or heterozygous pairing on the gene worksheet.
    2. Repeat this process for all of the traits represented.
    3. Then, color in the calf on the calf color page to reflect the genes passed on from the parents to the offspring.
    4. Have 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?
    5. In their groups, have students calculate the percent of animals that look like Herefords, Angus or crossbreds. Is there an even number of each? Why or why not?
  4. As a group, have students discuss:
    1. What are some objectives of ranchers selectively breeding cattle? What traits might they want to select for or against? How does this effect the consumer?
    2. How do genetics relate to the efficiency of the animal? How does that effect consumers?
    3. In an animal lives in an arid desert, what traits might you select for? What might help your animal be more successful in that environment?
    4. Do the traits we played the game for directly affect the animal’s use for consumers? What are some traits that might? Is there a way to select for traits that would focus on nutrition or healthfulness?
    5. Are beef producers the only farmers that need to worry about genetics? Are there traits in crops or other livestock that are affected by heredity? What might some of those be?

Essential Files (maps, charts, pictures, or documents)

Extension Activities

  • Have students brainstorm traits to add to the list. Some could include: muscle, bone, head color, hair length, hoof size, etc.  

Sources/Credits

Adapted from Oklahoma Agriculture in the Classroom

Author(s)

Kelsey Faivre, Will Fett

Organization Affiliation

Iowa Agriculture Literacy Foundation

Agriculture Literacy Outcomes

  • STEM Grade 3-5:
    • Identify examples of how the knowledge of inherited traits is applied to farmed plants and animals in order to meet specific objectives (i.e., increased yields, better nutrition, etc.)  
    • Provide examples of science being applied in farming for food, clothing and shelter products.

Education Content Standards

  • 3-LS3-1. Analyze and interpret data to provide evidence that plants and animals have traits inherited from parents and that variation of these traits exists in a group of similar organisms. [Clarification Statement: Patterns are the similarities and differences in traits shared between offspring and their parents, or among siblings. Emphasis is on organisms other than humans.] [Assessment Boundary: Assessment does not include genetic mechanisms of inheritance and prediction of traits. Assessment is limited to non-human examples.]
  • 3-LS3-2. Use evidence to support the explanation that traits can be influenced by the environment. [Clarification Statement: Examples of the environment affecting a trait could include normally tall plants grown with insufficient water are stunted; and, a pet dog that is given too much food and little exercise may become overweight.]
  • 3-LS4-2. Use evidence to construct an explanation for how the variations in characteristics among individuals of the same species may provide advantages in surviving, finding mates, and reproducing. [Clarification Statement: Examples of cause and effect relationships could be plants that have larger thorns than other plants may be less likely to be eaten by predators; and, animals that have better camouflage coloration than other animals may be more likely to survive and therefore more likely to leave offspring.]