Genetics: Inherited Traits Warm Up: 1. What are the major differences between asexual and sexual reproduction? 2. Which form of reproduction results in greater genetic variation (differences)? Explain why. 3. Explain why animals that reproduce sexually will never be an exact copy of one of the parents? 4. If you have a brother or sister from your same mother and father, why don’t you always have the same traits? Warm Up Answers: 1. What are the major differences between asexual and sexual reproduction? Asexual: One Parent. Offspring are an exact genetic copy of the parent (clones) unless a mutation occurs. Sexual: Two Parents. Half the offspring’s DNA comes from 1 male cell (sperm or pollen) and half comes from 1 female cell (egg) so they inherit traits from both parents. 2. Which form of reproduction results in greater genetic variation (differences)? Explain why. Sexual, because half the DNA comes from each parent rather than making an exact copy. You’re blending two different organisms rather than copying just one 3. Explain why organisms that reproduce sexually will never be an exact copy of one of the parents? The sperm/pollen and egg only have half a set of DNA so it would be impossible for one to make a copy on it’s own and have it develop into a new organism with a complete set. 4. If you have a brother or sister from your same mother and father, why don’t you always have the same traits? Each sperm/pollen cell and egg cell has a half set of DNA (1 of each chromosome) that will always contain a random combination so it’s nearly impossible (over a 1 in a million chance) you’d get two sperm and two eggs with the exact same set of genes that come together. The Case of the Endangered Critters Scientists have been doing research to better understand inherited traits on two islands in the middle of the ocean, far away from land and virtually untouched by humans. On one island they discover the only known population of blue tailed critters. On the other island they discover the only known population of orange tailed critters. The Case of the Endangered Critters The critter populations are shrinking on both islands and both have been classified as endangered species. Neither has ever been seen anywhere else in the world. Scientists know that the critters reproduce sexually and produce many offspring at a time. However, one of their natural predators, the black-billed yellowbird makes it difficult for young critters to survive in the wild. The Case of the Endangered Critters Critters are hard to capture, so very few exist in captivity. Skye is a blue-tailed critter and lives in the Petropolis Zoo. Poppy, an orange-tailed critter, lives in the Lawrenceville Zoo. The Case of the Endangered Critters The scientists have decided to try and cross-breed Skye and Poppy in order to produce offspring to try and help the critters populations from going extinct. Stop and Talk #1: What do you think Skye and Poppy’s offspring will look like? Why? The Case of the Endangered Critters The breeding program is a great success! Skye and Poppy produce 100 offspring! Stop and Talk #2: Why do you think all the offspring have blue tails? Do you think the orange tails will be lost forever? Why or why not? However, all 100 of these second-generation critters have blue tails, which concerns the scientists. They wonder, “will the orange tails be lost forever?” They argue about possible explanations. The Case of the Endangered Critters Further attempts to breed Skye and Poppy are unsuccessful. However, once their offspring begin to mature, scientists observe that they begin to have pups of their own. The scientists are fascinated by the results. Some of Skye and Poppy’s “grand-pups” have orange tails! In fact, about ¼ of this third generation have orange tails, while the other ¾ have blue tails. The Case of the Endangered Critters Stop and Talk #3: How would you explain what happened? The Case of the Endangered Critters Activity: Use the blue and orange chips on your table and the Critters Family Pedigree to create a visual model that you believe best demonstrates what might have happened with the genes Sky and Poppy passed on to their pups and grandpups. How did the orange tail in the third generation get there? Creating Genetic Variation Although offspring receive all their genes from their parents, the opportunity for variation is enormous. Think about your own family. If you have siblings, do they look like you? Creating Genetic Variation How closely do you resemble your parents or grandparents? Creating Genetic Variation An Australian monk named Gregor Mendel studied these kinds of inherited traits in pea plants in the 1860s. Based on the results of his experiments he proposed a model for how organisms inherit traits from their parents, which is still used today as the leading model for genetic inheritance. Stop and Talk #4: Do you think one of the tail color genes was dominant? If so, which one and what evidence do you have to support that? Mendel discovered that for many genes there is a dominant gene, meaning that if the two genes you get from your two parents for the same trait are different, there is one trait that will appear over the other. He also discovered that when there is a dominant gene then there is usually a recessive gene that will only appear if both the genes you get from both parents are for that recessive trait. Creating Genetic Variation We’re going to do a little experiment of our own to see how Mendel’s model works to help us predict the traits of offspring in sexual reproduction. For this simulation we’re going to pretend we’re looking at two of Skye and Poppy’s offspring, named Ocean and Lucy. Skye Ocean Poppy Lucy •Each offspring receives one version from each parent. Ocean and Lucy both have 1 blue gene from Skye and 1 orange gene from Poppy but both have blue tails. •Based on the fact that all 100 of Skye and Poppy’s offspring had blue tails, it’s safe to conclude that the blue-tail gene is dominant and the orange-tail gene is recessive. The Coin Toss Model of Mendel’s Theory •The outcome of a coin toss (heads or tails) represents the one version of a tail color gene that is contained in the gamete (sex cell: sperm or egg) contributed by a parent. Heads = Dominant Blue Gene (T) Tails = Recessive Orange Gene (t) •This means that if a pup gets: 2 Blue Genes (TT) then they will have a blue tail 1 Blue Gene and 1 Orange Gene (Tt) then they will have a blue tail 2 Orange Genes (tt) then they will have an orange tail •We would expect to get 75% with blue tails and 25% with orange tails because: Ocean’s Sperm Lucy Egg Offspring T (blue gene) T (blue gene) t (orange gene) t (orange gene) T (blue gene) t (orange gene) T (blue gene) t (orange gene) TT = blue TAIL Tt = blue TAIL tT = blue TAIL tt = orange TAIL Let’s Try It!! With your partner, make 10 pups and record how many have blue tails and how many have orange tails.