PPP_Ch. 3 b - CHAPTER 3 Mendelian Genetics Dr. Sanghamitra...

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Unformatted text preview: CHAPTER 3 Mendelian Genetics Dr. Sanghamitra Mohanty MAIN AREAS OF FOCUS: Mendels experiments to study patterns of inheritance Monohybrid cross Dihybrid cross Trihybrid cross Mendels postulates Laws of Probability Binomial theorem Chi-square analysis Pedigree analysis 3.1 3.1 Mendel Used a Model Experimental Approach to Study Patterns of Inheritance Mendel chose the garden pea as his model system because it is easy to grow, can be crossbred artificially, and grows to maturity in one season. Using seven visible features, each with two contrasting traits, and true-breeding strains, Mendel determined that discrete units of inheritance exist and predicted their behaviour during the formation of gametes. Monohybrid Cross Monohybrid crosses involve a single pair of contrasting traits. The original parents are the P 1 generation, and their offspring are the F 1 generation. Offspring arising from selfing (self-fertilizing) the F 1 generation are the F 2 generation. In the F 1 generation of a monohybrid cross, all of the plants have just one of the two contrasting traits. In the F 2 generation, 3/4 of the plants exhibit the same trait as the F 1 generation, and 1/4 exhibit the contrasting trait that disappeared in the F 1 generation. To explain these results, Mendel proposed the existence of particulate unit factors for each trait. He suggested that these factors (now called genes ) are passed unchanged from generation to generation, determining various traits expressed by each individual plant. Mendels monohybrid crosses were not sex dependent. For example, it did not matter whether a tall male plant pollinated a dwarf female plant, or vice versa. The results were the same either way. This is called a reciprocal cross . Mendel proposed three postulates of inheritance: Unit factors exist in pairs. In the pair of unit factors for a single characteristic in an individual, one unit factor is dominant and the other is recessive. The paired unit factors segregate (separate) independently during gamete formation . . The genotype is the genetic makeup of an individual. The phenotype is the physical expression of the genetic makeup. When the alleles (alternative forms of a single gene) for a trait in an individual are the same, the individual is homozygous . If the alleles differ, the individual is heterozygous . Genetic Terminologies A Punnett square allows the genotypes and phenotypes resulting from a cross to be visualized easily. A testcross is a way to determine whether an individual displaying the dominant phenotype is homozygous or heterozygous for that trait. Questions: Q: If the allele for green pod color (G) is dominant over the allele for yellow pod color (g), which of the following genotypes would a...
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This note was uploaded on 07/04/2011 for the course BIO 325 taught by Professor Saxena during the Fall '08 term at University of Texas at Austin.

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PPP_Ch. 3 b - CHAPTER 3 Mendelian Genetics Dr. Sanghamitra...

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