BIOL 3451 1st Edition Lecture 4Outline of Last Lecture 3.1 Mendel Used a Model Experimental Approach to Study Patterns of Inheritance3.2 The Monohybrid Cross 3.3 Mendel’s Dihybrid Cross Generated a Unique F2 Ratio3.4 The Trihydrid Cross3.5 Mendel’s Work Was Rediscovered in the Early 20th Century3.6 Independent Assortment Leads to Extensive Genetic Variations.3.7 Laws of Probability3.8 Chi-square Analysis3.9 Pedigrees Reveal Patterns of Inheritance of Human Traits.Outline of Current 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 ratioCurrent Lecture4.1 Alleles alter phenotypes in Different ways Allele: alternative form of a gene The wild type allele is the allele that is consider normal in the population, so the one that occurs the most frequently. All the mutation at a locus is compared the wild type. In order to recognize a new allele, the phenotype need to change. Loss-of-function mutation: when the function that it has is reduce or lost. If the lost is complete, the result of the mutation is called a null allele.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. Gain-of-function mutation: produce a phenotype different from the one that the normal allele. Neutral mutation: the chance in the allele will make no change in the phenotype.4.2 Geneticists use a variety of symbols for alleles Dd where D refers to the dominant allele and d refer to the recessive allele. Drosophila melanogaster was used to study the difference between wild-type and mutant traits. The + is for the wild type. The slash indicate that the 2 alleles have thesame locus. For ebony, the wild type can have the symbol of + only. Cyclin-dependent kinase (cdk) involve in the cell-cycle regulation4.3 Neither allele is dominant in imcomplete, or partial dominance Neither of the allele is recessive so no lower and upper case.  Tsay-Sachs disease: Jewish related disease. Hexosaminidase A: enzymes normally involved in lipid metabolism. Threshold effect: when a certain level of gene product is attained, normal phenotypic expression occurs. Threshold for Tsay-Sachs diseases is less than 50%4.4 Co dominance Co dominance: when the phenotype express is a mix of both alleles in a heterozygous. Genotype is 1:2:2:1  The difference between co dominance and dominant is the expression of BOTH traits in co dominance.4.5 Multiple alleles of a gene may exist in a population Multiple allele: when one gene has 3 or more alleles in the same population. Multiple alleles can be studied in a population. An example is the ABO bloodgroup inheritence in human. In blood, A and B are anti-gene. Control different genelocated on chromosome 9. The O blood type doesn’t havesugar terminals. The Bombay Phenotype: a lady was blood type B but was functioning as a type O. She had a rare recessive mutation named FUT1 which prevents her of synthesizing the complete H substance.4.6 Lethal alleles represent essential genes Recessive lethal allele: people with homozygous recessive will not survive. Dominant lethal allele: the presence of just 1 copy of the allele cause death of the person. Huntington disease is a dominant autosomal allele (H) when (Hh) the disease is delayed till adulthood. Around 40 years old. If everybody that are affected die before reproduction, the mutation will disappear from the population.4.7 Combinations of two gene pairs with two modes of inheritance modify the 9:3:3:1 ratio Two mode of inheritance occurring simultaneously. Genetic linkage: character located on the same chromosome. The ratio WILL NOT give a 9:3:3:1