GEN 3022 1st Edition Lecture 7 Outline of Last Lecture I Mitosis a Description b Diploid Cells c Phases II Meiosis a Description III The Chromosome a Definition b Locus c Chromatids d Formation of Chromosomes IV Chromosome Theory of Inheritance a Mendel s Law of Segregation b Mendel s Law of Independent Assortment V Cytogenetics a Definition b Karyotypes c Spectral karyotyping These 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 Determination VII X Linked Inheritance a Description b Punnett Squares Outline of Current Lecture I Introduction a Simple Mendelian Inheritance b Complexity of Inheritance II Wild Type Alleles a Wild type i Definition ii Two explanations for the wild type phenotype iii Example b Genetic polymorphism c Mutant alleles i Definition ii Dominant mutants 1 Gain of function 2 Dominant negative 3 Haploinsufficiency III Incomplete Penetrance a Definition b Ex Polydactyly c Degree of Penetrance IV Expressivity a Definition b Factors V Environmental Effects a Definition and examples i Coat color ii PKU b Temperature sensitive mutations i Example Siamese cats VI Incomplete Dominance a Definition b Example flower color VII Overdominance a Definition b Example Sickle Cell Anemia VIII Multiple Alleles a Definition b Example blood type c Codominance IX X linked Genes a Review b Reciprocal Cross X Lethal Alleles a Definition b Essential and nonessential genes c Conditional lethal alleles d Semilethal alleles XI Gene interactions a Gene interations b Epistasis c Note XII Complementation XIII Gene Redundancy a Definition b Gene knockout c Paralogs Current Lecture I II Introduction a Simple Mendelian Inheritance involves a single gene with two different alleles that display in a dominant recessive relationship b Complexities of Inheritance i There are many deviations from the simple mendelian inheritance model ii These deviations still obey Mendelian Laws of inheritance Wild Type Alleles a Wild type allele prevalent alleles in a population that encode for normal functioning proteins b Wild type phenotype two explanations III i 50 of the normal protein is enough to accomplish the protein s cellular function ii The heterozygote may actually produce more than 50 of the functional protein normal gene is up regulated to compensate for lack of function of the defective allele biological selection iii 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 populations d Mutant Alleles i Alleles that are altered by mutation and are passed between generations usually recessive and harmful to the individual ii 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 tweaks it usually harmful 2 Dominant negative protein encoded by the mutant gene acts antagonistically to the normal protein 3 Haploinsufficiency mutant involves loss of function of the protein and heterozygote does not make enough product to give the wild type phenotype Incomplete Penetrance a When a dominant allele does not always influence the outcome of a trait in a heterozygote individual b Example Polydactyly i Autosomal dominant trait where affected individuals have additional fingers and or toes ii A single copy of polydactyly allele is usually sufficient to cause the condition iii Sometimes individuals carry the dominant allele but don t exhibit the trait c Degree of Penetrance i 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 penetrant iii Note in any particular individual the trait is either present or not there is no in between d Expressivity i Degree to which a trait is expressed ex in polydactyly the number of digits can vary An individual with high expressivity may have multiple IV V VI VII extra digits while an individual with low expressivity may have only one extra digit ii Factors the environment and other modifier genes genes that change the function of a protein Environmental Effects a When the environment selects for genes that positively impact the phenotype of an individual i Coat color the arctic fox has a grayish brown coat in summer and white in winter ii 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 Mutations i Example Siamese cats have a temperature sensitive mutation in the gene encoding the tyrosinase enzyme required for synthesis of melanin pigment only occurs in extremities ii cooler temperatures active enzyme black coloration in the tail ears face and legs Incomplete Dominance a The heterozygote exhibits a phenotype that is intermediate between the corresponding homozygotes still obeys Mendel s laws but not simple Mendelian inheritance b Example wild type allele for red flower color crossed with recessive allele for white flower color produces a pink flower phenotype Overdominance a The phenomenon in which a heterozygote is more vigorous than both of the corresponding homozygotes aka heterozygote advantage b Example Sickle Cell Anemia i Originally an autosomal recessive disorder in which affected individuals have abnormally shaped sickle shaped hemoglobin ii Two alleles HbA encodes for normal hemoglobin and Hbs encodes for sickle shaped hemoglobin iii Having a heterozygous genotype is advantageous because having an allele for 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 malaria Multiple Alleles a Commonly found within natural populations typically three or more alleles that present unique genotypic and phenotypic combinations i Note for genes present in a single copy haploid genome a maximum of two alleles are found in any particular diploid individual b Blood type i ABO blood type is determined by the antigen s on the cell surface of red blood cells RBCs ii There are three different alleles that determine which antigens are present on the surface