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.


academics MCAT study skills SAT medical school admissions expository writing English college admissions GRE GMAT LSAT MD/PhD admissions chemistry math physics ACT biology writing language learning strategy law school admissions graduate admissions MBA admissions creative writing homework help MD test anxiety AP exams interview prep summer activities history philosophy career advice academic advice premed ESL economics grammar personal statements study schedules law statistics & probability PSAT admissions coaching computer science organic chemistry psychology SSAT covid-19 CARS legal studies logic games USMLE calculus parents reading comprehension 1L Latin Spanish dental admissions DAT engineering excel political science French Linguistics Tutoring Approaches research DO MBA coursework Social Advocacy case coaching chinese classics genetics kinematics skills verbal reasoning ISEE academic integrity algebra business business skills careers geometry medical school mental health social sciences trigonometry 2L 3L Anki FlexMed Fourier Series Greek IB exams Italian MD/PhD programs STEM Sentence Correction Zoom amino acids analysis essay architecture art history artificial intelligence astrophysics athletics biochemistry capital markets cell biology central limit theorem chemical engineering chromatography climate change curriculum data science dental school diversity statement finance first generation student functions gap year harmonics health policy history of medicine history of science integrated reasoning international students investing investment banking mba meiosis mitosis music music theory neurology phrase structure rules plagiarism presentations pseudocode secondary applications sociology software software engineering teaching tech industry transfer typology virtual interviews writing circles