Linkage and association mapping in genetic analysis

academics biology genetics
By Ryan R.

When geneticists want to see how closely related two genes are, they have two main ways of doing so: linkage analysis and association mapping. 

Linkage analyses use observation of phenotypes, or traits that can be observed, that are built into pedigrees, where the inheritance of specific traits are tracked in a family over time. Linkage refers to the fact that genetic markers or alleles of a gene that are close to each other on a chromosome generally segregate together. When alleles recombine (shuffle over) during meiosis, they are able to be inherited with a different chromosome, but this happens less often if the genes are closer to each other on the same chromosome. So, genetic markers (or alleles) that lie relatively far apart on a chromosome will undergo recombination more frequently than genetic markers that lie close to each other. These data are then made into genetic maps that correspond to the distance between different genes on a chromosome.  

Unlike linkage mapping, association mapping uses the newer technologies of DNA sequencing that allow scientists to identify many specific markers on a chromosome. Doing this over and over, and associating it with information from pedigrees, we can use our sequencing information to connect specific traits with a given sequence of DNA. Association mapping is generally carried out in the context of a whole genome, and this kind of study is called a Genome Wide Association Study (GWAS). Sequencing an entire genome is expensive, so instead, single nucleotide polymorphisms (SNPs) are used as molecular markers. SNPs are single sequence differences in DNA that are associated with a trait. For example, having an adenine at a given position in your DNA can be a SNP for having sickle cell anemia. Doing this thousands of times, with patients and controls, geneticists can identify individual or multiple genes responsible for traits, and start to find the locations of those genes on the chromosome. Unlike linkage analysis, which gives relative distances of genes, association mapping allows us to find the absolute position of genetic information.

Comments

topicTopics
academics study skills MCAT medical school admissions SAT expository writing college admissions English MD/PhD admissions GMAT LSAT GRE writing strategy chemistry physics math biology ACT graduate admissions language learning law school admissions test anxiety interview prep MBA admissions academic advice premed homework help personal statements AP exams career advice creative writing MD study schedules summer activities Common Application history test prep philosophy computer science secondary applications organic chemistry economics supplements PSAT admissions coaching grammar law statistics & probability psychology ESL research 1L CARS SSAT covid-19 legal studies logic games reading comprehension dental admissions mathematics USMLE Spanish calculus engineering parents Latin verbal reasoning DAT case coaching excel mentorship political science French Linguistics Tutoring Approaches academic integrity chinese AMCAS DO MBA coursework PhD admissions Social Advocacy admissions advice biochemistry classics diversity statement genetics geometry kinematics medical school mental health quantitative reasoning skills time management Anki English literature IB exams ISEE MD/PhD programs algebra algorithms art history artificial intelligence astrophysics athletics business business skills careers cold emails data science internships letters of recommendation poetry presentations resume science social sciences software engineering study abroad tech industry trigonometry work and activities 2L 3L Academic Interest DMD EMT FlexMed Fourier Series Greek Health Professional Shortage Area Italian Lagrange multipliers London MD vs PhD MMI Montessori National Health Service Corps Pythagorean Theorem Python STEM Sentence Correction Step 2 TMDSAS Zoom acids and bases amino acids analysis essay architecture argumentative writing brain teaser campus visits cantonese capacitors capital markets cell biology central limit theorem chemical engineering chess chromatography class participation climate change clinical experience community service constitutional law consulting cover letters curriculum demonstrated interest dental school distance learning electricity and magnetism enrichment european history executive function finance first generation student freewriting fun facts functions gap year genomics harmonics health policy history of medicine history of science hybrid vehicles hydrophobic effect ideal gas law induction information sessions institutional actions integrated reasoning intern international students investing investment banking lab reports logic mandarin chinese mba mechanical engineering medical physics meiosis microeconomics mitosis music music theory neurology neuroscience office hours operating systems organization pedagogy phrase structure rules plagiarism pre-dental proofs pseudocode psych/soc quantum mechanics resistors resonance revising scholarships school selection simple linear regression slide decks sociology software stem cells stereochemistry study spots synthesis teaching technical interviews transfer typology units virtual interviews writer's block writing circles