Lesson Plan Sexual Reproduction Using Chicken Eggs as a Model Materials/Resources Clear dishes or cups Magnifying glasses (not necessary but helpful) Unlined paper for drawing Information Summary: Fertilized vs. Unfertilized Eggs (pp.4-­‐5 of this document) Exit ticket (p. 6 of this document) Fertilized and unfertilized eggs If you get unfertilized eggs from somewhere other than the grocery store, you should candle those eggs first. Eggs in the grocery store are checked for blood spots before being packaged. Blood spots result from vascular or ovarian tissue remaining on the egg after it leaves the ovary. These spots could be mistaken for early embryonic development, so it’s best to be sure the unfertilized eggs are free of these blood spots. When candling these spots will show up as small dark spots in the egg. Teaching Strategies Observation and investigation Generating and testing hypothesis Scientific drawing Science Inquiry Skills Used Hands-­‐on, Minds-­‐on Reasoning/Induction Essential Questions What is the difference between diploid and haploid cells? What is a gamete? What is the role of a gamete in sexual reproduction? How are gametes related to the formation of a zygote? I Can Statements I can describe and differentiate haploid and diploid cells. I can explain how gametes are involved in sexual reproduction. I can describe a zygote and an embryo. Essential Vocabulary Sexual reproduction meiosis gamete fertilization DNA Lesson Steps: 1. Begin class by showing students eggs. Tell students that some of the eggs you have are gametes and some contain embryos. 2. Go over definition of gamete and zygote, and embryo. You can give the students the Information Summary sheet now, or give it to them after they have completed the lab, depending on which order will work best with your group of students. 3. Ask students how you could determine which eggs are gametes and which eggs contain embryos. Hopefully, someone will suggest that we need to look inside the egg. (If not, you can suggest this!) 4. Give each pair of students 2 eggs—1 fertilized egg and 1 unfertilized egg. 5. Instruct students to break the eggs into 2 different dishes, and then examine the egg contents. The embryo can usually be seen by the naked eye. They are more interesting with a magnifying glass, so it’s great if you have magnifying glasses available. Unfertilized eggs: Point out the very small white disk on the yolk. This is the germinal disc. This has the nucleus of the gamete, so the DNA is found here. Once a sperm fuses with nucleus of the egg the cell becomes a zygote. After the zygote begins dividing it becomes an embryo. 6. Instruct students to draw the fertilized egg and the unfertilized egg. For unfertilized egg label: yolk, white, germinal disc For fertilized egg label: yolk, white, embryo 7. Instruct students to complete lab questions. 8. Discuss and go over answers to lab questions in class. 9. Instruct students to complete exit ticket and turn in. Grade this to determine content mastery. Additional Assessments: These questions can be used as part of a larger assessment, or given to students separately as bell ringers. Describe an unfertilized egg using the terms: gamete, haploid, DNA, meiosis. Describe a fertilized egg using the words: zygote, DNA, diploid, embryo Information Summary Fertilized vs. Unfertilized eggs Many people wonder if the eggs they buy at the grocery store can hatch. Eggs that you buy at the grocery store are haploid, and therefore do not have two sets of genetic information. Since they only have one set of genetic information, they cannot develop into an embryo. A hen will produce eggs even if she has not mated with a rooster. This means that all that is needed to produce eggs from a chicken is a hen of reproductive age. (Recall that human females of reproductive age ovulate each month even if they are not sexually active). Hens kept only for the production of eggs are kept only with other hens, and are never mated with a rooster. For this reason, eggs purchased in grocery stores are unfertilized, meaning they are haploid and do not contain male gametes. In animals an egg is the female gamete. It is a reproductive cell which contains half of the genetic information (DNA) needed to make a new individual. A gamete is made from the process of meiosis. Gametes are haploid, and also referred to as 1n (a diploid cell is 2n). If an egg is fertilized, meaning that it contains both male and female gametes, the male gametes are introduced BEFORE the eggshell is formed. From the outside, an unfertilized egg looks just like a fertilized egg. Embryonic development of chickens occurs outside of the mother’s body, which is why a chicken egg is so much larger than a human egg (maximum size of a human egg is about 0.2mm). The chicken zygote must have all it needs for embryonic development within the egg on the day the egg is laid. In addition to being haploid, eggs in the grocery store have been refrigerated for a long period of time, and being very cold for an extended period of time will prevent a fertilized egg from developing. Most fertilized chicken eggs that are kept at temperatures between 50-­‐
70 degrees F can be successfully incubated if their temperature is raised to 99.5 degrees F within about 10 days. This evolutionary trait results from the fact that birds are able to lay a maximum of 1 egg per day. Normally a female bird will lay 1 egg per day until she has a group of eggs to incubate (this is called a clutch). The number of eggs in a clutch varies by species and is as small as 1 for a penguin to around 14 for some domestic species. She will then stop laying eggs and sit on the clutch of eggs to increase the temperature of the eggs and start embryonic development. Fertilized eggs become less likely to develop the longer they are help prior to incubation. For chickens, a few eggs will develop if the eggs are held for more than 10 days before incubation, but the percentage is much less than in eggs held for 10 days or less. Variations in temperature while the eggs are being held will also affect how many fertilized eggs will develop into embryos. Copyright: Natuculture Program, NCA&T State University Exit Ticket: Fertilized vs. Unfertilized Eggs 1. Is a gamete haploid or diploid? 2. _____________ reproduction requires specialized cells called gametes. 3. When a male and female gamete fuse (join together), they form a new cell called a ______________, which will then develop to become an embryo. 4. An unfertilized chicken egg contains only a female ____________. 5. A fertilized chicken egg contains both __________ and __________ gametes which have fused to form a zygote. 6. Are eggs from the grocery store haploid or diploid? Explain your answer. Exit Ticket: Fertilized vs. Unfertilized Eggs 1. Is a gamete haploid or diploid? 2. _____________ reproduction requires specialized cells called gametes. 3. When a male and female gamete fuse (join together), they form a new cell called a ______________, which will then develop to become an embryo. 4. An unfertilized chicken egg contains only a female ____________. 5. A fertilized chicken egg contains both __________ and __________ gametes which have fused to form a zygote. 6. Are eggs from the grocery store haploid or diploid? Explain your answer. Exit Ticket: Fertilized vs. Unfertilized Eggs 1. Is a gamete haploid or diploid? 2. _____________ reproduction requires specialized cells called gametes. 3. When a male and female gamete fuse (join together), they form a new cell called a ______________, which will then develop to become an embryo. 4. An unfertilized chicken egg contains only a female ____________. 5. A fertilized chicken egg contains both __________ and __________ gametes which have fused to form a zygote. 6. Are eggs from the grocery store haploid or diploid? Explain your answer.