BSCI222 Genetics Week 4 Chapter 5 Notes
BSCI222 Genetics Week 4 Chapter 5 Notes BSCI222
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This 4 page Class Notes was uploaded by Colin Fields on Sunday September 25, 2016. The Class Notes belongs to BSCI222 at University of Maryland taught by Dr. Paczolt in Fall 2016. Since its upload, it has received 3 views. For similar materials see Genetics in Biology at University of Maryland.
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Date Created: 09/25/16
BSCI222 Genetics Chapter 5 Extensions and Modifications of Basic Principles 1. 5.1 Additional Factors at a Single Locus Can Affect the Results of Genetic Crosses a. Types of Dominance i. Complete and Incomplete Dominance 1. Determined by where on a phenotypic scale a heterozygote falls 2. If the heterozygote expresses the phenotype of a homozygote then dominance is complete 3. If the heterozygote expresses a phenotype in between the homozygotes’ then dominance is incomplete ii. Codominance 1. The heterozygote expresses the phenotypes of both homozygotes iii. Level of Phenotype Observed May Affect Dominance 1. Anatomical, Physiological, and Molecular levels 2. A specific allele can display different types of dominance depending on which level is being examined b. Penetrance and Expressivity i. Sometimes a specific genotype does not always produce a specific phenotype ii. Penetrance: The percentage of individuals having a genotype that express the expected phenotype iii. Expressivity: Magnitude at which a phenotype is expressed c. Lethal Alleles i. Causes death at an early stage of development so these genotypes will not show up in progeny d. Multiple Alleles i. More than 2 possible alleles for a trait ii. Inheritance patterns not affected iii. Compound Heterozygotes 1. Organisms that carry two different alleles that results in a recessive phenotype 2. 5.2 Gene Interaction Takes Place When Genes at Multiple Loci Determine a Single Phenotype a. Gene Interaction: expression of a phenotype from one gene depends on the presence of another gene at a different locus b. Gene Interaction That Produces Novel Phenotypes i. Genes at two or more loci that produce phenotypes for the same trait (color for example) can produce 4 different phenotypes for the same trait in a dihybrid cross c. Gene Interaction with Epistasis i. Epistasis: one gene masks the effect of another gene at a different locus ii. Recessive Epistasis 1. One gene encodes for some trait and a second gene encodes for something important for making the phenotype of the first gene visible 2. A recessive version of gene 2 will prevent the phenotype of gene 1 from being visible thereby masking it iii. Dominant Epistasis 1. The same as recessive epistasis just with a dominant masking instead iv. Duplicate Recessive Epistasis 1. Two different alleles both suppress a phenotype if either on is homozygous recessive d. Complementation: Determining Whether Mutations Are at the Same Locus or at Different Loci i. Complementation test 1. Tests if recessive mutations are allelic 2. Cross of homozygous recessive, 1 of each phenotype 3. If allelic then there will be mutant offspring 4. If not allelic then there will be wild offspring ii. Complementation is when an organism with two recessive mutations possesses a wild type phenotype 3. 5.3 Sex influences the Inheritance and Expression of Genes in a Variety of Ways a. Sex-Influenced and Sex-Limited Characteristics i. Sex-influenced are characteristics inherited autosomally but expressed differently based on sex chromosomes ii. Sex-limited are characteristics that are autosomally inherited but expressed only in one sex b. Cytoplasmic Inheritance i. Genetic material found in the cytoplasm (mitochondria and chloroplasts notably) gets passed down through the cytoplasm ii. Can produce mosaics c. Genetic Maternal Effect i. The phenotype of an offspring is determined by the genotype of the mother not the offspring d. Genomic Imprinting i. Differential gene expression depending on which parent a gene is from ii. Epigenetics 1. Changes in how genes are expressed based on alterations to the DNA but not its sequence 4. 5.4 Anticipation Is the Stronger or Earlier Expression of Traits in Succeeding in Generations a. Changes to DNA that accumulate over time produce increasingly more expressive phenotypes 5. 5.5 The Expression of a Genotype May Be Affected by Environmental Effects a. Environmental Effects on the Phenotype i. Temperature sensitive 1. Allele product activation or inactivation depends on the temperature of the environment ii. Phenocopy 1. Environmental conditions alone can produce a phenotype normally expressed because of a specific genotype b. The Inheritance of Continuous Characteristics i. Characteristics with a few easily distinguishable phenotypes are discontinuous ii. Characteristics that exhibit a spectrum of phenotypes are continuous 1. Also called quantitative characteristics iii. Characteristics encoded by genes at many loci are polygenic iv. Pleiotropy is when one gene affects multiple characteristics v. Multifactorial characteristics are caused by multiple factors
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