BIOL 3451 1st Edition Lecture 6Outline of Last Lecture4.8 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 inheritance an individual’s sex influences the phenotype4.13 Genetic background and the environment may alter phenotypic expressionOutline of Current Lecture 5.1 Chromosome linked on the same chromosome segregate together5.2 Determining the distance between genes in chromosome mapping5.3 Determining the gene sequence during mapping5.4 When distance between 2 genes increases5.6 Lod Score analysis and Somatic cell hybridization5.7 Chromosome mapping5.9 Exchanges also occur between sister chromatids5.10 Linkage and mapping studiesCurrent Lecture5.1 Chromosome linked on the same chromosome segregate together Complete linkage: produce parental gametes, and NO crossing over occurs. Both are form in equal proportion. Recombinant gametes (crossover): when 2 nonsister chromatids out of the 4 chromatids present in the tetrad crossover. The number of linkage group should match with the haploid number of chromosomes.5.2 Determining the distance between genes in chromosome mapping Thomas A. Morgan was the first one to discover X-linkage. When single crossover occurs, 2 sister chromatids are involved and the 2 other remain unchanged.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. 50% is the theoretical limit of observed recombinaison possible due to crossing over.5.3 Determining the gene sequence during mappingMultiple exchanges Double crossovers (DCOs): double exchange of genetic material. The closer of each other are the 2 loci, the less likely it is that they will do crossover. The product law: probability of 2 independents event occur simultaneously. Chance of double crossover to occur is less than single cross over.Three-point Mapping in Drosophila Three criteria to execute a success mapping cross:1. The genotype of the organism producing the crossover gametes must be heterozygousat all loci under consideration. It homozygosity occurred at any locus. All gametes produced would contain the same allele, precluding mapping analysis.2. The cross must be constructed so that the genotypes of all gametes can be accurately determined by observing the phenotypes of the resulting offspring.3. A sufficient number of offspring must be produced in the mapping experiment to recover a representative sample of all crossover classes. The 2 non-crossover phenotypes are most easily recognized because they occur in the greatest proportion of offspring. Double crossover phenotype: 2 independent but simultaneous single-crossover events. The distance between x and y is equal to the percentage of ALL detectable exchange between them. The distance is given in mu (unit).Determining the Gene Sequence There are 2 possible methods for determining the genes order from a 3 point cross. Figure 5.9 is an example for the first method5.4 When distance between 2 genes increases Not always possible to detect all the crossover that occurred. Theorically, the frequency of crossover is proportional to the distance between any 2 locialong the chromosome, however, the degree of inaccuracy increases as the distance between the locus increases. The coefficient of coincidence (C) refers to the disparities that result from interference. € C =Observed DCOExpected DCO After founding C, we can calculate the quantify interference using € I = 1 − C. If I=1 it means that the interference was complete and no double crossover occurred. When I is +, positive interference occurred. When I is -, negative interference occurred.5.6 Lod Score analysis and Somatic cell hybridization JUST know the concept of Lod score for the exam. Lod score method helps demonstrate linkage. It helps assigning human genes to specific chromosomes and in constructing preliminary human chromosome maps.5.7 Chromosome mapping DNA markers: Short segment of DNA with a known sequence and location Restriction fragment length polymorphisms (RFLPs) and microsatellites are examples of DNA markers. Cyctic fibrosis gene was located using DNA markers. Other example of human diseases found using DNA markers: Type 1 and 2 diabetes, Crohn’s disease, hypertension, coronary artery disease, bipolar disorder, and rheumatoidarthritis.5.9 Exchanges also occur between sister’s chromatids Identification and study on sister chromatids exchanges are facilited by staining techniques. Harlequin chromosomes: sister chromatids with patterns of alternating patches. DNA helicase: play a role in DNA replication.5.10 Linkage and mapping studies Mapping the centromere: experimentally determining the frequency of recombination using tetrad data. Ordered tetrad analysis is not