Experiment8-Genetics

Experiment8-Genetics - Experiment 8 (Lab Periods 9 and 12)...

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Experiment 8 (Lab Periods 9 and 12) Genetics and the analysis of inheritance Genetics is the study of inheritance that traces its scientific beginning to the work undertaken by Gregor Mendel. It was Mendel who proposed the concept of what we now know as genes, although he did not use this term, in order to explain the inheritance of different traits in the pea plants that he worked with. His proposal was that each physical trait of an organism is the result of the action of a separate gene and that different forms of a gene (known as alleles) give rise to different forms of a trait, such as differences in flower color that he studied. In addition to the concept of genes, Mendel proposed certain ‘laws’ about the action of these genes. The first was the Law of Segregation. This Law was based on Mendel’s explanation of inheritance, which proposed that every individual received two copies of each gene, one from each parent. When that individual in turn passed on it’s genes, only one copy of each gene would be passed to each offspring. Mendel proposed that the two copies segregated to different gametes at this stage such that each gamete only contained a single copy. The two copies were restored in the offspring by the fusion of two gametes, each carrying a single copy. Mendel’s second Law concerned the interaction of different genes and stated that when two genes segregate, the segregation of the first gene (first pair of alleles) will be independent of the segregation of the second pair of alleles. This means that we can study the inheritance of the two traits separately. We now know that although Mendel gave us the first insight into the correct mechanism of inheritance, his proposals were much simpler than the reality. With respect to the second law, we now know that there are many exceptions to Mendel's two laws. For example genes can be on the same chromosome so that they do not segregate independently but stay together, or remain "linked". Mendel never noticed an exception since the traits he happened to study were not linked. In addition, the concept of individual traits being determined by separate genes is now known to be an oversimplification. In reality, each trait is influenced by the action of many different genes and every gene influences many different traits. However, in many cases we are able to study how a particular gene influences a specific trait, even though many other genes also play an important role. In this lab, you should keep in mind when examining specific traits that although you are only considering the action of a single gene it is not the only gene affecting that trait. In this lab you will follow the inheritance of several traits in the experimental organism Drosophila melanogaster , or the fruit fly. This is one of the most common lab organisms, particularly for genetic studies, since fruit flies grow quickly (a new generation emerges in about 2 weeks), produce many offspring and are easy to maintain. In addition, there is now a great
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Experiment8-Genetics - Experiment 8 (Lab Periods 9 and 12)...

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