Name____________________________________________ Ms. Sameroff Class__________ Date______________ Objective: SWBAT explain the purpose of selective breeding. DONOW NOW DO VOCABULARY ACTIVITY #1 Activity #2 Exit DO NOW 1. Vocabulary- Use your worksheet to define the words below. Selective Breeding Hybridization Inbreeding ACTIVITY #1 Background Information: Selective Breeding is the process by which humans breed animals or plants to achieve desired traits. This is typically carried out with domesticated organisms, however, humans have bred wild animals as well. There are two common methods of selective breeding-hybridization and inbreeding. Hybridization is a form of selective breeding that has been around for as long as man has lived and worked with domesticated animals. Hybrids are bred by mating two species of organisms (usually plant or animal) that belong to the same genus. The offspring will have traits that both parents exhibit. Inbreeding is used to maintain desirable characteristics in a line of organisms, breeders often use inbreeding, the continued breeding of individuals with similar characteristics. 1 People selectively breed animals and plants in order to make animals grow bigger, faster, prettier and stronger. Selective breeding also produced crops that have desirable traits. Although there are many positive aspects there is one major drawback for hybrids; most are sterile, meaning that they are derived from parents with different numbers of chromosomes and the parent chromosomes have different structures. These differences cause an issue when the hybrid 2 makes gametes, or sex cells, during meiosis. The chromosomes have difficulty pairing up during meiotic division because of their structural and numerical variations and thus the sex cells are created inconsistently, making the sperm and egg unviable. Their uniqueness dies with them. Questions 1. A farmer has bred his pineapple plants from the sweetest pineapples from his last harvest to get even sweeter pineapple plants. What is this an example of? Explain your answer. __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ 2. What are some problems associated with selective breeding? __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ 3. Explain the two most common methods of selective breeding. (Use this sentence starter! The two most common methods of selective breeding are…) __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ THINK, PAIR, SHARE Do you think selective breeding is ethical (morally good or correct)? Explain your answer. __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ __________________________________________________________________________________________________ Activity #2 Selective Breeding of Corn The history of modern-day maize begins at the dawn of human agriculture, about 10,000 years ago. Ancient farmers in what is now Mexico took the first steps in domesticating maize when they simply chose which kernels (seeds) to plant. These farmers noticed that not all plants were the same. Some plants may have grown larger than others, or maybe some kernels tasted better or were easier to grind. The farmers saved kernels from plants with desirable characteristics and planted them for the next season's harvest. This process is known as selective breeding or artificial selection. Maize cobs became larger over time, with more rows of kernels, eventually taking on the form of modern maize. The identity of maize's wild ancestor remained a mystery for many decades. While other grains such as wheat and rice have obvious wild relatives, there is no wild plant that looks like maize, with soft, starchy kernels arranged along a cob. The abrupt appearance of maize in the archaeological record baffled scientists. Why did maize appear so suddenly? 3 Through the study of genetics, we know today that corn's wild ancestor is a grass called teosinte. Teosinte doesn't look much like maize, especially when you compare its kernals to those of corn. But at the DNA level, the two are surprisingly alike. They have the same number of chromosomes and a remarkably similar arrangement of genes. In fact, teosinte can cross-breed with modern maize varieties to form maize-teosinte hybrids that can go on to reproduce naturally. Scientists study teosinte-maize hybrids and their offspring through the process of genetic archaeology. This process helps geneticists understand what is happening at the DNA level to make teosinte and maize so different. By combining clues from genetics and the archaeological record, scientists have pieced together much of the story of maize selective breeding. One of the first scientists to fully appreciate the close relationship between teosinte and maize was George Beadle. In the 1930s, Beadle studied teosinte-maize hybrids and showed that their chromosomes are highly compatible. Later, he produced large numbers of teosinte-corn hybrids and observed the characteristics of their offspring. By applying basic laws of genetic inheritance, Beadle calculated that only about 5 genes were responsible for the most-notable differences between teosinte and a primitive strain of maize. Using more-modern techniques, another group of scientists analyzed the DNA from teosinte-maize offspring. They too noticed that about 5 regions of the genome (which could be single genes or groups of genes) seemed to be controlling the most-significant differences between teosinte and maize. In recent years, geneticists have used advanced molecular-biology tools to pinpoint the roles of some of the genes with large effects, as well as many other regions across the genome that have had subtle effects on maize domestication. The earliest events in maize domestication likely involved small changes to single genes with dramatic effects. We know the events were early because there is little variation in these genes between maize varieties, suggesting that modern varieties are descended from a single ancestor. That the small changes had dramatic effects also explains the sudden appearance of maize in the archaeological record. Later changes in the selective breeding of modern maize involved many genes (perhaps thousands) with small effects. These minor changes include the following: Types and amounts of starch production Ability to grow in different climates and types of soil Length and number of kernel rows Kernel size, shape, and color Resistance to pests Local groups of farmers selected for characteristics that they preferred, and that worked best in their particular environment. Over thousands of years, selective breeding generated the broad diversity of corn varieties that are still grown around the world today. READING QUESTIONS (Answer in complete sentences!) 1. How did ancient farmers in Mexico contribute to the selective breeding of corn/maize? (Hint: What did they notice? What did they do?) 2. What is the wild ancestor of corn and how is it genetically similar to corn? 4 3. How did the scientist George Beadle contribute to our understanding of corn’s genetics? 4. What other traits does modern corn have as a result of selective breeding? REGENTS QUESTIONS EXIT TICKET After the lesson, now I understand… Something I still need help with… 5 6 7 EXIT TICKET After the lesson, now I understand… ___________________________________________________________________________________________ ___________________________________________________________________________________________ Something I still need help with… ___________________________________________________________________________________________ 8
