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U of M GCD 3022 - Complexities of Mendelian Inheritance and Gene Interaction

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GEN 3022 1st Edition Lecture 7Outline of Last Lecture I. Mitosisa. Descriptionb. Diploid Cellsc. Phases II. Meiosisa. DescriptionIII. The Chromosomea. Definitionb. Locusc. Chromatidsd. Formation of ChromosomesIV. Chromosome Theory of Inheritancea. Mendel’s Law of Segregationb. Mendel’s Law of Independent AssortmentV. Cytogeneticsa. Definitionb. Karyotypesc. Spectral karyotypingThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.VI. Human Sex DeterminationVII. X-Linked Inheritancea. Descriptionb. Punnett SquaresOutline of Current Lecture I. Introductiona. Simple Mendelian Inheritanceb. Complexity of InheritanceII. Wild-Type Allelesa. Wild-typei. Definitionii. Two explanations for the wild-type phenotypeiii. Exampleb. Genetic polymorphismc. Mutant allelesi. Definitionii. Dominant mutants1. Gain of function2. Dominant negative3. HaploinsufficiencyIII. Incomplete Penetrancea. Definitionb. Ex: Polydactylyc. Degree of PenetranceIV. Expressivitya. Definitionb. FactorsV. Environmental Effectsa. Definition and examplesi. Coat colorii. PKUb. Temperature sensitive mutationsi. Example: Siamese catsVI. Incomplete Dominancea. Definitionb. Example: flower colorVII. Overdominancea. Definitionb. Example: Sickle Cell AnemiaVIII. Multiple Allelesa. Definitionb. Example: blood typec. CodominanceIX. X-linked Genesa. Reviewb. Reciprocal CrossX. Lethal Allelesa. Definitionb. Essential and nonessential genesc. Conditional lethal allelesd. Semilethal allelesXI. Gene interactionsa. Gene interationsb. Epistasisc. NoteXII. ComplementationXIII. Gene Redundancya. Definitionb. Gene knockoutc. ParalogsCurrent LectureI. Introductiona. Simple Mendelian Inheritance: involves a single gene with two different alleles that display in a dominant/recessive relationshipb. Complexities of Inheritancei. There are many deviations from the simple mendelian inheritance modelii. These deviations still obey Mendelian Laws of inheritanceII. Wild-Type Allelesa. Wild-type allele: prevalent alleles in a population that encode for normal functioning proteinsb. Wild-type phenotype: two explanationsi. 50% of the normal protein is enough to accomplish the protein’s cellular functionii. The heterozygote may actually produce more than 50% of the functional protein (normal gene is “up-regulated” to compensate for lack of functionof the defective allele): biological selectioniii. If the dominant allele (wild-type) is purple flower color and the recessive allele is white then the purple allele will work its way into the population c. Genetic Polymorphism: where there is more than one wild-type in large populationsd. Mutant Allelesi. Alleles that are altered by mutation and are passed between generations; usually recessive and harmful to the individualii. Dominant mutants (much more rare than recessive mutants)1. Gain of function: protein encoded by the mutant gene changes its function(mutant gene gains original function of protein but tweaksit, usually harmful)2. Dominant negative: protein encoded by the mutant gene acts antagonistically to the normal protein3. Haploinsufficiency: mutant involves loss of function of the protein and heterozygote does not make enough product to give the wild type phenotypeIII. Incomplete Penetrancea. When a dominant allele does not always influence the outcome of a trait in a heterozygote individualb. Example: Polydactylyi. Autosomal dominant trait where affected individuals have additional fingers and/or toesii. A single copy of polydactyly allele is usually sufficient to cause the conditioniii. Sometimes individuals carry the dominant allele but don’t exhibit the traitc. Degree of Penetrancei. There is variation in how often a trait will penetrate a phenotype (appear in the phenotype with just one dominant allele)ii. Example: if 60% of heterozygotes carrying a dominant allele exhibit the trait allele, the trait is 60% penetrantiii. Note: in any particular individual the trait is either present or not, there isno in betweend. Expressivityi. Degree to which a trait is expressed; ex: in polydactyly the number of digits can vary. An individual with high expressivity may have multipleextra digits while an individual with low expressivity may have only one extra digitii. Factors: the environment and other ‘modifier’ genes (genes that change the function of a protein)IV. Environmental Effectsa. When the environment selects for genes that positively impact the phenotype of an individuali. Coat color: the arctic fox has a grayish brown coat in summer and white inwinterii. PKU (phenylketonuria): makes it so that the individual is unable to metabolize phenylalanine, which can be counteracted by consuming a strict diet (environmental factor)b. Temperature Sensitive Mutationsi. Example: Siamese cats have a temperature sensitive mutation in the geneencoding the tyrosinase enzyme (required for synthesis of melanin); pigment only occurs in extremitiesii. cooler temperatures = active enzyme = black coloration in the tail, ears, face, and legsV. Incomplete Dominancea. The heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes (still obeys Mendel’s laws, but not simple Mendelianinheritance)b. Example: wild-type allele for red flower color crossed with recessive allele for white flower color produces a pink flower phenotypeVI. Overdominancea. The phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes (aka heterozygote advantage)b. Example: Sickle Cell Anemiai. Originally an autosomal recessive disorder in which affected individuals have abnormally shaped (sickle shaped) hemoglobinii. Two alleles: HbA encodes for normal hemoglobin and Hbs encodes for sickle shaped hemoglobiniii. Having a heterozygous genotype is advantageous because having an allelefor sickle cell anemia will give the individual some sickle cells but not enough to have a negative impact on the individual, but having a normal allele makes the individual resistant to malariaVII. Multiple Allelesa. Commonly found within natural populations; typically three or more alleles that present unique genotypic and phenotypic combinationsi. Note: for genes present in a single copy/haploid genome, a maximum of two alleles are found in any particular diploid individualb. Blood typei. ABO blood type is determined by the antigen(s) on the cell surface of red


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