Definition
What is genetic linkage?
Genetic linkage is the tendency of genes, or other DNA sequences, that sit near each other on the same chromosome to be passed on together. Linked genes break Mendel's law of independent assortment: instead of producing every combination of alleles in equal numbers, a parent mostly passes on the allele combinations it inherited, which are called parental types.
Linkage is not absolute, because of crossing over. During meiosis, paired homologous chromosomes swap segments, and a crossover that falls between two genes creates recombinant gametes carrying new combinations of alleles. The farther apart two genes are, the more often this happens. The share of recombinant offspring, called the recombination frequency, therefore works as a measure of distance: 1 percent recombination equals 1 centimorgan, or map unit. It tops out at 50 percent, the value seen for genes that are not linked at all.
Working with fruit flies in Thomas Hunt Morgan's lab, Alfred Sturtevant used this idea in 1913 to draw the first genetic map. Linkage studies in families later helped locate many genes behind inherited diseases, and linked markers remain a key tool in genome-wide studies.
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Where does the term “genetic linkage” come from?
- gen-
- birth, originGreek genesis
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Terms that go with it
- ChromosomeA chromosome is a thread-like structure of DNA and protein that carries an organism's genes; most human cells hold 46 of them in 23 pairs.
- MeiosisMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- Mendelian inheritanceMendelian inheritance is the pattern by which single genes pass from parents to offspring, following the laws of segregation and independent assortment.
- GeneA gene is a stretch of DNA that carries the instructions for making a protein or a working RNA molecule, and is the basic unit of heredity.
- Genome-wide association studyA genome-wide association study (GWAS) scans the genomes of many people to find genetic variants that are more common in those with a trait or disease.
- AlleleAn allele is any of the alternative forms of a gene or DNA sequence that can occupy the same position, or locus, on a chromosome.
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Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Linkage
- OpenStax Biology 2e, 13.1 Chromosomal Theory and Genetic Linkage
- OpenStax Biology 2e, 12.3 Laws of Inheritance
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