Selectively Breeding Sheep - Lesson Plan

Estimated Time

One 60-minute class period

Student Learning Targets

Students will calculate probabilities using Punnett squares.

Students will use provided materials to research Spider Lamb Syndrome.

Students will apply their understanding of calculating probabilities of inheritance via Punnett squares and their understanding of inheritance of Spider Lamb Syndrome to analyze risk.

Key STEM Ideas

All plants, animals, and humans are born with a different, but specific set of chromosomes which contain DNA. DNA stands for deoxyribonucleic acid. It is special, because it holds the code for every cell in your body. Every cell in your body uses DNA as an instruction manual to control the specific makeup of an organism. Within each string of DNA are sets of instructions called genes. A gene tells a cell how to make a specific protein. The proteins are used by the cell to perform certain functions, to grow, and to survive.

Inheritance is a biological process in which parents pass genes onto their children or offspring. Every offspring inherits genes from both of their biological parents and these genes in turn express specific traits. Some of these traits may be physical for example hair and eye color and skin color etc. On the other hand some genes may also carry the risk of certain diseases and disorders that may pass on from parents to their offspring.

Students' Prior Knowledge

Students should have a good understanding of basic inheritance and how genes are passed on from parent to offspring. Students should have basic skills in statistics and probability. Students do not need to have any knowledge of sheep. The lesson includes a quick overview of Mendelian inheritance, Punnett squares, and sheep.

Connections to FEWSS

Sheep are ruminant animals raised for meat and wool. According to the American Sheep Industry Association (2015), there are 5.28 million head of sheep in the United States. There are over 200 breeds of sheep that are selectively bred to serve specific purposes.

While sheep are bred for desirable traits, occasionally, other genetic diseases or disorders may be passed along to offspring as well. Spider Lamb Syndrome (SLS) in sheep is a recessive genetic disorder. It causes skeletal deformities including bent limbs and twisted spines. It is difficult for sheep breeders to eliminate the risk of SLS in a flock because parents of SLS lambs do not exhibit any symptoms. This is a recessive disorder, so both parents must carry a recessive allele in order for the lamb to be affected.

Sheep producers have the difficult task of using a combination of selective breeding techniques and DNA tests to eliminate this genetic trait from their animals. DNA tests can be expensive, so instead of purchasing DNA tests for an entire flock, breeders can test certain sheep and use Punnett Squares to predict the probability of other sheep in the flock of carrying the recessive allele.

For more information: Purdue University Fact Sheet on Spider Lamb Syndrome: http://ag.ansc.purdue.edu/sheep/ANSC442/Semprojs/spider/spider.html

Curriculum ConnectionsNext Generation Science Standards

• HS-LS3-1. Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring.
• HS-LS3-3. Apply concepts of statistics and probability to explain the variation and distribution of expressed traits in a population.

Common Core Standards

• CCSS.ELA-Literacy.RST.9-10.4 - Determine the meaning of symbols, key terms, and other domain-specific words and phrases as they are used in a specific scientific or technical context relevant to grades 9-10 texts and topics.
• CCSS.ELA-Literacy.RST.9-10.7 - Translate quantitative or technical information expressed in words in a text into visual form (e.g., a table or chart) and translate information expressed visually or mathematically (e.g., in an equation) into words.
• CCSS.Math.Content.HSS.IC.A.2 - Decide if a specified model is consistent with results from a given data-generating process, e.g., using simulation.
• CCSS.Math.Content.HSS.MD.B.7 - Analyze decisions and strategies using probability concepts