BIOL 3451 1st Edition Lecture 5Outline of Last Lecture 4.1 Alleles alter phenotypes in Different ways4.2 Geneticists use a variety of symbols for alleles4.3 Neither allele is dominant in imcomplete, or partial dominance4.4 Codominance4.5 Multiple alleles of a gene may exist in a population4.6 Lethal alleles represent essential genes4.7 Combinations of two gene pairs with two modes of inheritance modify the 9:3:3:1 ratioOutline of Current Lecture 4.8 Phenotypes are often affected by more than one gene4.9 Complementation analysis4.10 Expression of a single gene may have multiple effects4.11 X-linkage describes genes on the X chromosome4.12 ln sex-linked and sex-influenced inheritancem an individual’s sex influences the phenotype4.13 Genetic background and the environment may alter phenotypic expressionCurrent Lecture4.8 Phenotypes are often affected by more than one gene Gene interaction: several genes influence a particular characteristic. Doesn’t mean that it can be apply to all genes. Ex: eye development Epigenisis: each step of development increase the complexity of the organ or feature of interest and is controlled by many genes.Epistasis Expression of one gene pair masks or modifies the effect of another gene pair. Look example in the Book!Novel PhenotypesThese 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. F2 generation will have a 9:6:1 ratio Example or gene interaction because 2 genes influence the fruit shape equally. Another exemple is the eye color in Drosophila melanogaster Ommatidia: individual visual units that make up compound eye4.9 Complementation analysis Complementation analysis: allow us to determine if 2 independently isolated mutations are in the same gene (alleles) or if they represent mutations in separate genes. Used to screen if any number of mutation will end up giving the same phenotype. Complementation group: all mutations are present in any single gene With this technique, it is possible to predict the total number of genes involved in the determination of that trait.4.10 Expression of a single gene may have multiple effects Marfan syndrome: human disease that result from autosomal dominant mutation in he gene encoding the connective tissue protein fibillin. Porphyria variegata: people who has this can’t adequately metabolize the porphyrin component of hemoglobin when this respiratory pigment is broken down as red blood cells are replaced. Most of the mutations when expressed manifest more than a single time.4.11 X-linkage describes genes on the X chromosome White eyes mutations in Drosophila. Red eyes wild type is dominant to white color. White locus is present on the X chromosome, not Y. Both the gene and the trait is X-linked. Homozygous mother pass it to ALL of their sons, but not all of their daughter. Chromosome theory of inheritance: thecorrelation between Mendel’s work and thebehavior of chromosomes during meiosis. X-linked in human: they can observe easilybecause of the criss-cross in the pedigree. Ex: Color blindness. Duchenne muscular dystrophy: onset before 6 years old, lethal around 20. Normally occurs in males.4.12 ln sex-linked and sex-influenced inheritance an individual’s sex influences the phenotype Doesn’t matter if on X or Y chromosome, some expression of the phenotype only express in a certain sex. (sex-limited inheritance) Expression are modified by the individual’s sex hormones. Another example of a sex-limited inheritance is the breast milk.4.13 Genetic background and the environment may alter phenotypic expressionPenetrance and Expressivity De degree of expression of the gene can be determined by penetrance and expressivity Ex: If 15% of flies with a given mutant genotype show the wild-type appearance, the mutant gene is said to have a penetrance of 85%. Expressivity reflects the range of expression of the mutant genotype.Genetic Background: Positive Effects. The actual location of the gene can depend on where it is in relation to other geneticmaterial. Heterochromatin: if a gene is relocated to OR near certain areas of the chromosome that are condensed and genetically inert.Temperature effects – An Introduction to Conditional Mutations Phenotype can be influenced by the temperature They are called temperature-sensitive mutations Conditional mutation: phenotype expression depends on environmental conditionsNutritional Effects Phenotype doesn’t always reflect the genotype. Ex: mutation in biosynthetic pathway Ex: Phenylketonuria: cant metabolize the amino acid phenylalanine Ex: Galactosemia: can’t metabolize galactose Ex: Lactose intolerance: can’t metabolize lactoseOnset of Genetic Expression Tsay-Sachs disease Lesch-Nyhan syndrome Duchenne muscular dystrophy (DMD) Huntington diseaseGenetic Anticipation Genetic anticipation: Become more severe when passing on to future generations Myotonic dystrophy: most common dystrophy muscular in