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Unit 2: Inheritance of Traits Through the Chromosomes 52 Unit 2: Inheritance of Traits Through the Chromosomes (6 hours) Introduction The work of Gregor was instrumental in the study of inheritance. His methods were novel and he used ingenious ways in order to get his results. He did not even know what he was looking at but he still managed to discern its behavior all the same. He was methodical and he was a hard worker. All these are common characteristics of great scientists through the ages. Most people of his time did not take him seriously because he was a monk but Mendel had a scientific mind and that was all that is really needed when people want to do research. His contributions were instrumental in establishing the field of genetics, which is now deeply embedded in so many fields in and out of biology. Years after Mendel, the chromosomes were finally observed. Similar to what happened to Mendel, many people did not think the chromosomes – and the DNA that they had inside – had important functions in the cell. Many did not think such simple colored bodies seen under the microscope were actually one of the most important components of any living thing. As the techniques for cell biology and microscopy progressed, it became very clear what Mendel had actually observed and how chromosomes fit into that. The chromosomes were finally shown as the physical basis for Mendel’s laws. The chromosomes and DNA were finally given the recognition they deserved. This unit focuses on Mendel’s findings, exceptions to his laws of inheritance and some diseases that follow Mendelian inheritance patterns. We will also focus on chromosomes and how their behavior ties in to the observations Mendel made. Lastly, inheritance of sex-linked traits will also be given focus. Learning Outcomes for the Unit At the end of this unit, you will be able to: a. explain the rationale behind Mendel’s experimental design.
Unit 2: Inheritance of Traits Through the Chromosomes 53 b. describe Mendel’s laws of inheritance and their physical basis given our knowledge today. c. learn how to do a mating or cross using a Punnett square and determine possible genotypes and phenotypes of the offspring. d. make use of probabilities to solve simple genetics problems. e. enumerate instances that are exceptions to Mendelian inheritance. f. understand the concept of nature versus nurture and how it affects an organism’s phenotype. g. construct and decipher family pedigrees. h. describe Morgan’s experiments and how they provide evidence for the chromosome theory. i. explain the chromosomal basis of sex. j. differentiate the inheritance of traits in autosomes and those in sex chromosomes. k. understand linked genes and how they are inherited. l. describe a gene linkage map. m. describe how DNA outside the nucleus is inherited. Topics Recommended for Review To make it easier for you to understand the topics being discussed in the module, it is recommended that you refresh yourself on the following topics: 1. Cell structure: This module assumes you have stock knowledge of the parts of a prokaryotic cell and a eukaryotic cell. Please try to be knowledgeable about the structures of these cells as well as the membrane-bound organelles you find in animal cells. Please take extra note of the machinery that takes part in cell division. 2. Probabilities in mathematics: Please review how to calculate probabilities. This should have been tackled in your previous mathematics subjects. Review how probabilities are expressed (both fractions and percentages).
Unit 2: Inheritance of Traits Through the Chromosomes 54 Topic 4: Mendel’s Laws of Inheritance The prevailing theory for inheritance during Gregor Mendel’s time was that traits from the parents blended and were passed on to their offspring. The theory of pangenesis, initially proposed by Darwin, one of the more acclaimed scientists at the time, was the more accepted theory. There were still people who questioned Darwin’s pangenesis theory and Darwin himself acknowledged the flaws in his ideas. While he was pondering on the solution to this, little did he realize that the answers he was seeking were already being made in an abbey hundreds of miles away. Gregor Mendel’s work was pioneering in the field of genetics. Unfortunately, it would be decades before people fully appreciated the work he was doing. This topic focuses on the findings made by Mendel and how such studies can be applied to our study of genetics. Learning Objectives At the end of this topic, you will be able to: a. understand the concepts underlying Mendelian inheritance. b. understand how probabilities may be used to predict inheritance patterns in genes following Mendelian inheritance. c. make use of probabilities to solve simple genetics problems. d. construct pedigree charts to follow the inheritance of certain traits. e. identify some diseases that follow Mendelian inheritance Presentation of Content Mendel’s experimental design Mendel’s work documented a particulate mechanism for inheritance. Unlike the blending model that was more accepted at the time, Mendel showed that traits were inherited separately and independently from each other. He developed his theory of inheritance long before scientists even knew that chromosomes existed. Mendel grew up in his parent’s farm in Austria so he was not ignorant of agricultural knowledge. He was taught agriculture in addition to his basic education when he was a young child. He excelled in high school and later in the Olmutz Philosophical Institute. It was in 1843 that a 21-year old Mendel entered an Augustinian monastery. He tried to become a teacher but was unable to pass the examinations. He decided to pursue college for a span of two years in 1851 and studied physics and chemistry at the University of Vienna. Two of