The Science of Maryland Agriculture

Transcription

1 Edition 3 (2016) GOAL STATEMENT: Students will learn how to predict plant and animal offspring traits or characteristics using genetics. Note: Students will need to have previous knowledge of basic genetics, particularly the principles of inheritance and dominant/recessive traits, before participating in this lesson. OBJECTIVES: Students will apply the concepts of genotype and phenotype to scenarios involving agricultural animals. Students will utilize Punnett squares to make predictions about the genotype and phenotype of offspring resulting from parent animals and will make breeding decisions based on these findings. REQUIRED MATERIALS: Check Out Your Genetic Traits worksheet (1 per student) Agricultural Animal Genetics worksheet (1 per student) AMOUNT OF TIME TO ALLOW: minutes. Extension activities will take additional time. University of Maryland Extension programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, or gender identity or expression.

2 Take a few seconds to look at everyone in the room. Chances are that no two people look exactly the same. In fact, it s very likely that most people look very different from one another. This is because almost every person in the world has their own unique set of genes that make them look the way they do. Identical twins are the only people who share the same exact genes with another person everyone else is completely unique! Just like humans have genes, animals have genes, too. An animal s genes determine many different things including coat color, height, whether or not they have horns, and so much more! Animal breeders have to pay careful attention to genetics to make sure the animals they breed will create offspring with desired traits. Some genes are dominant, meaning they mask the expression of other genes. Other genes are recessive and are only sometimes expressed in the offspring. Animal breeders need to have a solid understanding of genetics in order to make good decisions about which individuals to breed. Following are some important vocabulary terms to understand when discussing parents and offspring in terms of animal breeding. Sire male parent (father) Dam female parent (mother) Cow a female bovine Bull an intact male bovine Calf a young bovine Mare a female horse Stallion an intact male horse Foal a young horse Sow a female pig Boar an intact male pig Piglet a young pig University of Maryland Extension programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, or gender identity or expression.

3 10 minutes Use the Check Out Your Genetic Traits worksheet as a warm-up activity. Have students complete independently and then compare answers with a partner. After reviewing their responses, ask students to raise their hands if they have the same color hair as one of their parents. Use this to lead into a review conversation about inheritance of traits. Then have students brainstorm genetic traits that can be inherited in agricultural animals. In Maryland, there are many plants and animals that are part of the agriculture industry. For example, did you know that there are over 87,000 horses in the state of Maryland? Horses come in a variety of sizes and coat colors. Coat colors include: black; chestnut (red); bay (brown with black mane, tail, muzzle, ear tips, and legs); gray; palomino (yellow with blond mane and tail); and sorrel (light brown) just to name a few. Maryland is home to approximately 200,000 cows, and they too come in a variety of colors. In addition, some cows have horns and some do not have horns (polled). Some cows have genes to produce large quantities of milk while others have been genetically selected to produce meat. All of these traits coat color, polledness, and milk and meat production are controlled by genes that can be passed from parent to offspring. This lesson will explore how animal breeders use genetics to guide breeding decisions in order to produce animals with desired traits. 35 minutes 1. Have students complete the vocabulary and Punnett square reviews on the Agricultural Animal Genetics worksheet independently, then review the answers as a class. 2. Next, assign students into small groups, and assign a breeding scenario to each group. If the class is large, you may wish to assign the same scenario to more than one group. 3. Allow groups several minutes to discuss their scenarios and to prepare a short explanation that they will present to the class. 4. Have groups present and discuss each scenario as a class. 15 minutes Have student groups share their breeding scenarios with the class and explain how they came to their conclusions. Reference the teacher s guide for answers and explanations to each breeding scenario. University of Maryland Extension programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, or gender identity or expression.

4 Horse breeders often want to produce offspring with specific coat colors, such as with the tobiano horse example in the lesson. There are many colors and variations possible in terms of horse coats. Breeders must have an understanding of the genetics governing color traits in order to produce foals with their desired coat color or pattern. Have students research different coat colors and patterns and the genes that govern them and present their findings to the class. You may have students develop word problems like in the lesson and have other students complete the problems. Consult the following resources to learn more about the genetics of horse coat colors. Basic Horse Genetics (ANR-1420) from the Alabama Cooperative Extension System. Visit <store.aces.edu> and search for Basic Horse Genetics. Introduction to Coat Color Genetics from the University of California-Davis Veterinary Genetics Laboratory. Visit <vgl.ucdavis.edu> and search for Introduction to Coat Color Genetics. American Paint Horse Association s Guide to Coat Color Genetics from the American Paint Horse Association. Available at <press.apha.com/pdfs/guidebooks/colorgenguide.pdf> Coat Color Calculator, an interactive tool from Animal Genetics, Inc. Visit <animalgenetics.us,> choose the equine link, and open the Coat Color Calculator. Geneticist This person conducts research to help scientists gain a better understanding of genetics such as how and why cells mutate or which traits can be passed from parent to offspring. Some geneticists work in the medical field to help people who have special genetic conditions. Crop Geneticist This person creates new crop varieties by crossbreeding specific seeds, usually selecting for better traits like improved quality or increased yield. Animal Breeder This person manages the breeding and reproduction of animals, usually selecting two parents that will produce offspring with better traits like higher milk production or faster muscle growth. Student understanding can be evaluated through class discussion or assessment of completed activity data sheets. The following questions may also be used to evaluate student learning. 1. Explain the difference between phenotype and genotype. 2. List three heritable traits that are of particular interest to farmers. Why are these traits considered more important than some other traits? 3. Some, but not all, traits are heritable. Plan an experiment that would help you determine whether a certain trait of interest is heritable in a particular species. University of Maryland Extension programs are open to all and will not discriminate against anyone because of race, age, sex, color, sexual orientation, physical or mental disability, religion, ancestry, national origin, marital status, genetic information, political affiliation, or gender identity or expression.

5 A A Name: Date: Period: Which of the following traits did you inherit from your parents? Check which trait best describes you. 1. Hair type Curly Straight 2. Little finger Bent Straight 3. Hair on the back of your fingers No hair on fingers Hair on the fingers With a partner, check to see which of these traits best describes you. 4. Tongue rolling Can roll tongue Can t roll tongue 1 5. Ear lobes Unattached (A) Attached (B) B 6. Widow s peak Widow s peak (A) No widow s peak (B) B 1 Child rolled tongue by Gideon Tsang is licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license.

6 Name: Match the terms below with the correct definitions. Agricultural Animal Genetics - Vocabulary Review 1. Dominant gene A. The observable traits of an organism, such as coat color 2. Recessive gene B. One copy of a gene; an organism gets one from each parent 3. Allele C. Is masked when two alleles differ; is expressed when two alleles are identical 4. Phenotype D. When two alleles are identical 5. Genotype E. When two alleles are different 6. Heterozygous F. Is always expressed, whether the two alleles are identical or different 7. Homozygous G. The genetic makeup of an organism

7 Name: Agricultural Animal Genetics - Punnett Square Review A Punnett square is a simple way to predict the traits of offspring that will be produced when two specific individuals are mated. The genotype of one parent is listed down the side of the square, and the genotype of the other parent is listed across the top. The potential genotypes for offspring are written in the four boxes inside the square. B b Genotype of one parent Genotype of other parent B B BB BB Bb Bb Scrapie is a fatal genetic disease that affects the nervous system of sheep. Scrapie is an infectious disease, but some animals are genetically immune. The scrapie gene (Q) is recessive to the scrapie-resistant gene (R). Complete the Punnett square below to determine the possible genotypes that could be produced by mating a ewe (female sheep) with genotype QR to a ram (male sheep) with genotype RR. What percentage of the offspring from this mating will be scrapie-resistant?

8 Name: Date: Period: Agricultural Animal Genetics - Polledness in Cattle Some cattle have horns, and some don t. Cattle born without horns are called polled. Polledness is a desirable trait because horns can be dangerous and make managing cattle more difficult. The polled gene (P) is dominant to the horned gene (p). (Note that horns are different from antlers. Horns are present on animals like cattle and goats; males and females can have horns, and they are not shed. Antlers are present on animals like deer and moose; only males have antlers, and they are shed every year.) State the phenotype and possible genotypes for the animals pictured below. Phenotype: Possible genotype(s): You are a cattle breeder with a herd of polled cattle. Although you prefer polled cattle, you just inherited a new bull (male animal) that has horns. Complete the Punnett squares below to determine the percentage of offspring from your polled cows (females) that you can expect to be born with horns. (Hint: there are two Punnett squares because your polled cows may have two different possible genotypes. Assume your herd is made up of equal numbers of cows with each genotype.) New bull Phenotype: Possible genotype(s): New bull Your cows Percentage with horns: Percentage with horns: Total percentage of offspring with horns:

9 Name: Agricultural Animal Genetics - Polledness in Cattle (2) After breeding the horned bull this year, you will sell him and buy a different bull to breed next year. You have identified three potential bulls to buy. Cheston is polled. Both his sire (father) and dam (mother) were also polled. Wyeth has horns. His sire was polled, and his dam had horns. Naylor is polled. His sire was polled, and his dam had horns. You want to produce polled calves. Recall that your herd is made up of both polled and horned cows. Which bull is the best choice, and why?

10 Name: Agricultural Animal Genetics - Tobiano Coat in Horses Tobiano is a coat marking pattern in horses in which the horse has broad white patches of hair over the entire body. Tobiano is a unique coat pattern, so people who breed tobiano horses prefer to produce foals with the tobiano marking. The tobiano gene (T) is dominant. State whether each of the following horses will produce a tobiano foal if bred with a horse that is not tobiano. Genotype: TT Genotype: Tt Genotype: tt You are a horse breeder who raises Arabian horses. Arabians do not carry the tobiano gene, but you want to begin producing crossbred horses that have a tobiano coat pattern. You would like to buy a colt (young male horse) to breed to your solid-coated mares (female horses), and you have identified three potential choices. Merlin has a tobiano coat, and his dam (mother) has a solid coat. Jasper has a solid coat, and his dam has a tobiano coat. Tucker has a tobiano coat, and his dam has a tobiano coat. First, determine the genotype of each of the three colts. (Hint: for one colt, there will be two possibilities.) Merlin: Jasper: Tucker:

11 Name: Agricultural Animal Genetics - Tobiano Coat in Horses (2) Next, use a Punnett Square to determine the likelihood that each of the three colts will produce a tobiano offspring when bred to a mare with a solid coat. Merlin Jasper Tucker Your mare You want to buy the colt with the highest likelihood of producing offspring with tobiano coats. Which colt is the best option?

12 Name: Agricultural Animal Genetics - Porcine Stress Syndrome in Pigs Porcine stress syndrome (PSS) is a genetic disorder in pigs that causes sudden death when pigs are exposed to stress. Meat from pigs with PSS is also negatively affected and can be either soft and watery or dark and dry. The gene for PSS is recessive (n). State whether animals with each of the following genotypes will exhibit PSS. Circle the genotype of the animal who is a carrier. NN Nn nn You are a pig producer with ten sows (female pigs). You know that your sows do not carry any alleles for the PSS gene because you have had them all genetically tested for the disease. Last year you bred your sows to Brutus, a neighbor s boar (male pig). Once the piglets were mature, you decided to keep some as breeding animals and sent some to market. Some of Brutus s offspring that you sent to market produced pale, watery meat. What is the likelihood that this was caused by PSS? You are concerned that Brutus may have been a carrier of PSS. You ask your neighbor to have Brutus genetically tested, but she has already sent him to market. Brutus s meat appeared normal, but he may have been a carrier of PSS. Assuming Brutus was a carrier, complete the Punnett square to determine the percentage of his offspring with your sows that could be carriers of PSS. Your sows Brutus Percent of Brutus s offspring that may be carriers of PSS:

13 Name: Agricultural Animal Genetics - Porcine Stress Syndrome in Pigs (2) Your sows produced 80 piglets as a result of breeding with Brutus. Because you are expanding your pig breeding operation, you sent half of the offspring to market and kept the other half as breeding animals. However, you do not want to breed any pigs that carry the PSS gene. You could have all your breeding animals tested, but the genetic test is expensive. What is the least number of Brutus s offspring that you must have genetically tested in order to determine whether he was a carrier? Explain your answer.

14 TEACHER KEY: Agricultural Animal Genetics - Vocabulary Review Match the terms below with the correct definitions. F 1. Dominant gene A. The observable traits of an organism, such as coat color C 2. Recessive gene B. One copy of a gene; an organism gets one from each parent B 3. Allele C. Is masked when two alleles differ; is expressed when two alleles are identical A 4. Phenotype D. When two alleles are identical G 5. Genotype E. When two alleles are different E 6. Heterozygous F. Is always expressed, whether the two alleles are identical or different D 7. Homozygous G. The genetic makeup of an organism

15 TEACHER KEY: Agricultural Animal Genetics - Punnett Square Review A Punnett square is a simple way to predict the traits of offspring that will be produced when two specific individuals are mated. The genotype of one parent is listed down the side of the square, and the genotype of the other parent is listed across the top. The potential genotypes for offspring are written in the four boxes inside the square. B b Genotype of one parent Genotype of other parent B B BB BB Bb Bb Scrapie is a fatal genetic disease that affects the nervous system of sheep. Scrapie is an infectious disease, but some animals are genetically immune. The scrapie gene (Q) is recessive to the scrapie-resistant gene (R). Complete the Punnett square below to determine the possible genotypes that could be produced by mating a ewe (female sheep) with genotype QR to a ram (male sheep) with genotype RR. Q R R QR RR R QR RR What percentage of the offspring from this mating will be scrapie-resistant? 100%

16 TEACHER KEY: Agricultural Animal Genetics - Polledness in Cattle Some cattle have horns, and some don t. Cattle born without horns are called polled. Polledness is a desirable trait because horns can be dangerous and make managing cattle more difficult. The polled gene (P) is dominant to the horned gene (p). (Note that horns are different from antlers. Horns are present on animals like cattle and goats; males and females can have horns, and they are not shed. Antlers are present on animals like deer and moose; only males have antlers, and they are shed every year.) State the phenotype and possible genotypes for the animals pictured below. Phenotype: polled Possible genotype(s): PP or Pp Phenotype: horned or not polled Possible genotype(s): pp You are a cattle breeder with a herd of polled cattle. Although you prefer polled cattle, you just inherited a new bull (male animal) that has horns. Complete the Punnett squares below to determine the percentage of offspring from your polled cows (females) that you can expect to be born with horns. (Hint: there are two Punnett squares because your polled cows may have two different possible genotypes. Assume your herd is made up of equal numbers of cows with each genotype.) New bull New bull p p p p P Pp Pp P Pp Pp Your cows P Pp Pp P pp pp Percentage with horns: 0% Percentage with horns: 50% Total percentage of offspring with horns: 25%

17 TEACHER KEY: Agricultural Animal Genetics - Polledness in Cattle (2) After breeding the horned bull this year, you will sell him and buy a different bull to breed next year. You have identified three potential bulls to buy. Cheston is polled. Both his sire (father) and dam (mother) were also polled. Wyeth has horns. His sire was polled, and his dam had horns. Naylor is polled. His sire was polled, and his dam had horns. You want to produce polled calves. Recall that your herd is made up of both polled and horned cows. Which bull is the best choice, and why? Cheston is the best choice. Because both of his parents were polled, there is a chance that he is homozygous for the polled gene; Cheston s genotype is either PP or Pp. Naylor, however, cannot be homozygous for the polled gene because his mother had horns and did not carry the polled gene (pp); Naylor s genotype is Pp. Thus Cheston has a higher probability of producing polled calves. Wyeth is not a good choice because he has horns, meaning he does not carry the polled gene. Wyeth will only produce polled calves when bred to polled cows.

18 TEACHER KEY: Agricultural Animal Genetics - Tobiano Coat in Horses Tobiano is a coat marking pattern in horses in which the horse has broad white patches of hair over the entire body. Tobiano is a unique coat pattern, so people who breed tobiano horses prefer to produce foals with the tobiano marking. The tobiano gene (T) is dominant. State whether each of the following horses will produce a tobiano foal if bred with a horse that is not tobiano. Genotype: TT Genotype: Tt Genotype: tt You are a horse breeder who raises Arabian horses. Arabians do not carry the tobiano gene, but you want to begin producing crossbred horses that have a tobiano coat pattern. You would like to buy a colt (young male horse) to breed to your solid-coated mares (female horses), and you have identified three potential choices. Merlin has a tobiano coat, and his dam (mother) has a solid coat. Jasper has a solid coat, and his dam has a tobiano coat. Tucker has a tobiano coat, and his dam has a tobiano coat. First, determine the genotype of each of the three colts. (Hint: for one colt, there will be two possibilities.) Merlin: Tt Jasper: Tucker: YES MAYBE NO tt TT or Tt Next, use a Punnett Square to determine the likelihood that each of the three colts will produce a tobiano offspring when bred to a mare with a solid coat.

19 TEACHER KEY: Agricultural Animal Genetics - Tobiano Coat in Horses (2) Merlin Jasper Tucker T t t t T T (or t) t Tt tt t tt tt t Tt Tt Your mare t Tt tt t tt tt t Tt Tt You want to buy the colt with the highest likelihood of producing offspring with tobiano coats. Which colt is the best option? Tucker is the best option. We do not know Tucker s genotype; he could be either Tt or TT. We do know Merlin s and Jasper s genotypes. If Tucker is Tt, he has a 50% chance of producing a tobiano offspring. Merlin has the same chance. However, if Tucker is TT, he has a 100% chance of producing tobiano offspring.

20 TEACHER KEY: Agricultural Animal Genetics - Porcine Stress Syndrome in Pigs Porcine stress syndrome (PSS) is a genetic disorder in pigs that causes sudden death when pigs are exposed to stress. Meat from pigs with PSS is also negatively affected and can be either soft and watery or dark and dry. The gene for PSS is recessive (n). State whether animals with each of the following genotypes will exhibit PSS. Circle the genotype of the animal who is a carrier. NN no Nn no nn yes You are a pig producer with ten sows (female pigs). You know that your sows do not carry any alleles for the PSS gene because you have had them all genetically tested for the disease. Last year you bred your sows to Brutus, a neighbor s boar (male pig). Once the piglets were mature, you decided to keep some as breeding animals and sent some to market. Some of Brutus s offspring that you sent to market produced pale, watery meat. What is the likelihood that this was caused by PSS? The soft, watery meat was not a result of PSS. Genetic testing confirmed that all of your sows were genotype NN so they do not exhibit or carry the gene for PSS. If Brutus carried the PSS gene, the offspring could be carriers of PSS but would not exhibit symptoms. You are concerned that Brutus may have been a carrier of PSS. You ask your neighbor to have Brutus genetically tested, but she has already sent him to market. Brutus s meat appeared normal, but he may have been a carrier of PSS. Assuming Brutus was a carrier, complete the Punnett square to determine the percentage of his offspring with your sows that could be carriers of PSS. N Your sows N Brutus N n NN Nn NN Nn Percent of Brutus s offspring that may be carriers of PSS: 50%

21 TEACHER KEY: Agricultural Animal Genetics - Porcine Stress Syndrome in Pigs (2) Your sows produced 80 piglets as a result of breeding with Brutus. Because you are expanding your pig breeding operation, you sent half of the offspring to market and kept the other half as breeding animals. However, you do not want to breed any pigs that carry the PSS gene. You could have all your breeding animals tested, but the genetic test is expensive. What is the least number of Brutus s offspring that you must have genetically tested in order to determine whether he was a carrier? Explain your answer. You only need to have one positive result to know that Brutus was a carrier, but you can t be sure he wasn t a carrier unless you test Brutus. Theoretically only 50% of the offspring would be carriers, but in real life this may not be the result. The more negative results you see, the greater the likelihood that he was not a carrier.