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FIU BSC 1010L - Lab #8: Mendelian Genetics

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GENERAL BIOLOGY LAB 1 (BSC1010L)Lab #8: Mendelian GeneticsOBJECTIVES:INTRODUCTION:Monohybrid crosses and the law of segregationFigure 1. Schematic of Mendel’s law of segregationFigure 2. (a) Unattached (EE or Ee) vs. (b) attached earlobes (ee)BB: __________________________________Bb: ___________________________________TASK 1 – Patterns of Inheritance I: Simple DominanceFigure 3. Example of a Monohybrid crossProcedure:Table 1:Table 2:Figure 4. Pink snapdragons are an example of incomplete dominanceFigure 5. Different types of inheritanceFigure 6. Human ABO blood typesDihybrid crosses and the law of independent assortmentFigure 7. Schematic of Mendel’s law of independent assortment______________________________________________________________________________TASK 4 - Drosophila Virtual Genetics LabProcedure:TASK 5 - Testing Mendel’s laws of inheritance in Brassica rapaFigure 8. Possible F2 Genotypes and phenotypes for the Anthocyanin geneTable 7:Table 8:Example:Degrees of freedom: __________Probability of chance occurrence (from Table 9):________TASK 6 - Analyzing PedigreesFigure 10. Symbols used in pedigree analysisQuestions:LOOK AHEAD:REFERENCES:GENERAL BIOLOGY LAB 1 (BSC1010L)Lab #8: Mendelian Genetics______________________________________________________________________________OBJECTIVES:- Understand Mendel’s laws of segregation and independent assortment. - Differentiate between an organism’s genotype and phenotype.- Recognize different patterns of inheritance.- Perform monohybrid and dihybrid crosses.- Use pedigree analysis to identify inheritance patterns.______________________________________________________________________________INTRODUCTION:Through his studies of the inheritance patterns of the garden pea, Pisum sativum, Gregor Mendel changed our understanding of heredity. Mendel studied characters/traits that differed between plants and designed cross-fertilization experiments to understand how these characters transmit to the next generation. The results of Mendel’s work refuted the prevailing hypothesis ofblending inheritance and provided a new framework for understanding genetics. Ultimately, Mendel postulated two laws to explain heredity: (1) the law of segregation and (2) the law of independent assortment.Monohybrid crosses and the law of segregationThe law of segregation, also termed the “first law,” states that during gamete formation the alternate forms of a gene (i.e. alleles) on a pair of chromosomes segregate randomly so that each allele in the pair is received by a different gamete. For example, if you were to examine the gene responsible for petal color, you may discover that the gene can be expressed as either yellow or white flowers. In this scenario, the gene is petal color, while the alleles are yellow and white. Depending on which allele is expressed, petal color will vary. Examine Figure 1 below making sure that you can follow the path of each allele from parent to offspring. Figure 1. Schematic of Mendel’s law of segregation1In diploid organisms, all alleles exist in pairs; identical alleles within a pair are homozygous, while different alleles are heterozygous. Allele forms are represented by a single letter that explains whether a particular trait is dominant or recessive. Dominant alleles are assigned an uppercase letter (E), while recessive alleles are lowercase (e).In general, a dominant trait is expressed when at least one of the alleles present in the resulting allelic pair is dominant (EE or Ee). In contrast, for a recessive trait to be expressed, both alleles within the pair must be recessive (ee). For example, when considering ear lobe shape, two forms (attached and unattached) are apparent (Fig. 2). This trait is regulated by a single gene where unattached ear lobes are dominant (E) while attached ear lobes (e) are recessive. Figure 2. (a) Unattached (EE or Ee) vs. (b) attached earlobes (ee)An organism’s genotype (EE, Ee, ee) is the combination of alleles present whereas the phenotype is the physical expression of the genotype. In the earlobe shape example above, an individual can have a genotype of EE, Ee or ee. People with EE or Ee genotypes have the unattached earlobe phenotype (Fig 2a), while those with an ee genotype express the attached earlobe form (Fig 2b). Note that dominant traits can be either homozygous (EE) or heterozygous (Ee) while recessive traits are always homozygous (ee).Question: Given that the allele for brown eyes (B) is dominant and the allele for blue eyes (b) is recessive, which of the following genotypes would result in individuals with brown eyes? Which genotype(s) is/are homozygous and which is/are heterozygous?BB: __________________________________Bb: ___________________________________bb: ___________________________________2In today’s lab you will use the concepts of Mendelian Genetics to solve problems regarding inheritance. ______________________________________________________________________________TASK 1 – Patterns of Inheritance I: Simple Dominance Simple dominance is the term used to describe a common outcome of allelic combinations, where one allele, if present, will dominate over the other and will be expressed. Information about alleles present in a parental population can be used to determine the probability of different genotypic and phenotypic ratios for a variety of traits in the offspring. In instances when only 1 or 2 traits are being considered the Punnett square (Fig. 3) approach is used to predict the possible outcomes of the parental cross. When only one trait is being considered the cross is monohybrid while a dihybrid cross involves 2 traits. General instructions on how to perform a cross using the Punnett square approach:1. Write down the genotypes of the parents2. Note the gametes that each parent can contribute3. Draw a Punnett Square4. Across the top write the gametes that one parent contributes and along the side write the gametes contributed by the other parent 5. Perform the cross6. Determine the genotypic and phenotypic ratiosFigure 3. Example of a Monohybrid crossIn the example above (Fig. 3), the genotypic ratio is 1:2:1 (1: CC, 2: Cc, 1: cc) while the phenotypic ratio is 3:1. Since C = curly hair and c = straight hair, ¾ of the possible offspring willhave curly hair while only ¼ will have straight hair. 3Procedure:1. You will now simulate a cross between two heterozygous individuals, Tt and Tt. Each group should obtain two coins from your TA. You


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