3-2-1 Countdown to Genetics Objectives: In this laboratory you will: • Observe t

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3-2-1 Countdown to Genetics Objectives: In this laboratory you will: • Observe the inheritance of traits over three generations of plants. • Recognize contrasting phenotypes. • Propose and test models for the inheritance of the phenotypes. • Make predictions about the inheritance of the phenotypes. • Collect and analyze data from F2 seedlings. • Compare predicted results with results obtained from actual data. • Modify predictions based on new data.                                                                                            Introduction Wisconsin Fast Plants™, Brassica rapa, are widely used to study inheritance. There are several mutant types available for study, and they can be crossed by transferring pollen from the flower of one plant to the flower of another plant. You will germinate Wisconsin Fast Plants seeds collected from three generations of plants and make observations that will help you determine the pattern of inheritance. In sexual reproduction, two gametes fuse, bringing together homologous chromosomes from both parents. One chromosome of the homologous pair is inherited from the male parent and the other is inherited from the female parent. Since genes (the hereditary units) are located on the chromosomes, there are two copies of each gene. For example, Drosophila (fruit flies) have a gene for eye color, and there are two forms or alleles of this gene, Se, a dominant allele for red, and se a recessive allele for sepia (brown). If both alleles on the chromosome pair are for red (Se/Se) the phenotype (appearance or form that is observed) is red eyes and the genotype is homozygous. If the two alleles are different (Se/se), the phenotype is red eyes and the genotype is heterozygous. If the two alleles are for sepia (se/se), the phenotype is sepia eyes and the genotype is homozygous recessive. A cross involving one gene (one set of alleles) is a monohybrid cross. Monohybrid crosses usually involve parents that have one set of contrasting phenotypes. An example in corn would be crossing a red kernel corn with a yellow kernel corn. A cross between parents that differ in two separate genes (two separate sets of alleles) is a dihybrid cross. Dihybrid crosses usually involve parents that have two sets of contrasting phenotypes. An example of a dihybrid cross in corn would be crossing red, starchy kernel corn with yellow, sugary kernel corn. Here are some symbols that you will find useful in this investigation. P1 maternal parent or “mother” P2 paternal parent or “father” F1 the first-generation offspring that result from crossing of the P1 and P2; the children, so to speak. Short for first filial, a word that refers to offspring. F2 the second-generation offspring, the result of crossing two plants Observing the P1 and F1 Seedlings Observe the P1 and F1 seedlings in your petri dish. Record any consistent difference or differences between these two sets of seedlings. Compare your seedlings to those of other groups to be certain that all groups are seeing the same differences. What phenotypic differences do you notice between the P1 and F1 plants? Forming a Hypothesis and Making Predictions Base on your observations and general knowledge of genetics, state a hypothesis (model) on how these phenotypes are inherited. Be as complete as possible and cite evidence for or give a reason for each part of your hypothesis. Your hypothesis should include whether the phenotypes are inherited through a single set of alleles (monohybrid) or two sets of alleles (dihybrid). Include a one- or two-word designation for each phenotype and a symbol for the allele that gives rise to each phenotype. Indicate which allele of each pair is dominant and explain how you know. Each parent plant (P1 and P2) was homozygous for the alleles involved in the cross that you are studying. Given this information, use your hypothesis to predict the following (give your reasoning for each prediction): 1. the phenotype of the P1 and P2: 2. the genotype of the F1 3. the genotype of the F2 Testing Hypothesis and Predictions Your teacher will now explain what materials are available to you. Outline a procedure whereby you can use these materials to test your hypothesis. Include methods and expected outcomes. List at least two possible outcomes that could cause you to reject your hypothesis or modify it. Now set up your test. Observing F2 Seedlings Three days after setting up your test, retrieve your petri dish and inspect the F2 seedlings. Has this test confirmed your hypothesis? Explain your answer. Based on the results of your test, should you: 1. Accept your hypothesis without modification? If so, state your argument for accepting your hypothesis 2. Reject your hypothesis? If so, develop a new, detailed hypothesis to replace your old one. 3. Modify your hypothesis? If so, explain in detail your modification.

Explanation / Answer

Ans. This question is an experiment so we cannot write what was there in the pertridish of the student. Based on the knowledge on genetics we can say that one of the parent is always dominant over the other.The character which is expressed in first fillial generation is called dominant and the character which cannot be expressed is recessive.So to answer the question above lets say that the :father(P2) is having homozygous alleles for purple colour and round seeds (PPRR) and P1 (mother) is having recessive alleles for yellow and wrinkled seeds.Then F1 will be dominant heterozygous showing phenotype purple and round seeds(pprr).The genotype of the F1 generation will be PpRr.The second fillial generation is obtained by crossing the plants of F1 that is sefling.We cross PpRr * PpRr. as per mendels law of independent assortment the inheritance of one allele is independent of other allele.So the inheritance of seed colour is independent of seed shape (round or wrinkled).The gametes during crossing will be PR,Pr,pR,pr for both the parent and the cross will give ratio of 9:3:3:1 that is the ratio will be 9 purple and round,3purple and wrinkled, 3 yellow and round, 1yellow and wrinkled.

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