08 - January 31, 2013.docx

3 Pages

Molecular Genetics and Microbiology
Course Code
Johanna Rommens

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EXAM SOON – covers up to lecture 09 HW equilibrium In 1908 – independently described concept that in large randomly mating population where no selection, mutation or migration - allele frequencies and genotype frequencies are constant Simple relationship between genotype and allele frequencies BILALLE SYSTEM ONLY Expected genotype frequencies for AA is square of a allele frequency When testing for deviance from HWE – observed genotype data, calculate allele frequencies, calculate expected genotype frequencies under HWE and compare observed genotype frequencies to expected to see if statistically different If genotyping assay is producing incorrect results – perhaps because there is another genetic variation interfering with assay – cause deviation from HWE Infants data Estimates are very close between observed and expected Chi square test – p value of 1 – infants – no significant evidence of genotypes deviating from HWE Genotype data of adults – Observe more heterozygotes than expected; observe fewer SS; Statistical significance – significant deviation from HWE in adults WHY? Sickle cell anemia – death in childhood so fewer SS homozygotes as adults Excess of AS heterozygotes – these individuals have advantage: malaria survival Two violations of HWE – negative selection of rare homozygotes (dying faster than other genotypes); heterozygotes have survival advantage Prediction of carrier frequency Estimate allele frequency – according to Hardy Wineberg Equilibrium – to get allele frequency for S, take square root of genotype frequency 1 in 23 people are carriers Can calculate expected frequency of the normal homozygote – p squared – when calculating HWE – calculate expected frequencies of genotypes, should ADD UP TO ONE Under assumption of HWE – estimate frequency of carrier rate for autosomal recessive disease using principles of HWE – if really want to know carrier frequency, need gene for disease and the mutations that cause the disease – genotype in large population – estimate and make sure HWE applies Heterozygosity – heterozygous genotype frequency – determine which allele transmitted from parent to children Genetic linkage – cosegregation of genetic marker with either another marker or a trait (ex. Disease) because the two components are located relatively close to each other on the chromosome Meiotic recombination – basis of genetic linkage – presence of recombination destroys linkage – different chromosomes segregate independently, phenomenon of genetic linkage allows assignment of genetic markers and linkages to particular chromosomes, regions of chromosomes Genetic linkage important in human genetics – before attempt to identify gene causing human disease – need map of genetic variation in human genome – if had one polymorphism in particular gene and someone else had another polymorphism in another gene – do not know where located in genome unless able to measure polymorphisms in chromosomes – suggest on the same chromosome, close to each other – set of DNA that were distributed through community – genotype polymorphism in data set – share data with community – test linked to markers already generated Simple MEndlian diseases- genes identified with linkage analysis, which has been used for common diseases and quantitative traits ADPKD – 3HVR multi allelic Rsal
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