Linkage

The tendency for genes and other genetic markers to be inherited together because of their location near one another on the same chromosome. A gene is a functional physical unit of heredity that can be passed from parent to child. All genes in humans are pieces of DNA. Most genes contain information for making a specific protein. The term "genetic marker" is broader. A genetic marker is simply a segment of DNA with an identifiable physical location on a chromosome whose inheritance can be followed. A genetic marker can have a function and thus be a gene. Or a marker can be a section of DNA with no known function. Because DNA segments that lie near each other on a chromosome tend to be inherited together, markers are often used as tools for tracking the inheritance pattern of a gene that has not yet been identified but whose approximate location is known. The statistical estimate of whether two loci are likely to lie near each other on a chromosome and are therefore likely to be inherited together is called a LOD score. A LOD score of 3 or more is generally taken to indicate that the two loci are linked and are close to one another.

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1. A chemical covalent bond. 2. The relationship between syntenic loci sufficiently close that the respective alleles are not inherited independently by the offspring; a characteristic of loci, not genes.

- genetic l. l. (2).

- medical record l. the assemblage of lifetime or long-term individual medical histories from vital and medical data derived from multiple sources.

- record l. a method of assembling the information contained in two or more sets of medical records, or a set of medical records and vital records such as birth or death certificates, and a procedure to ensure that each individual's records are counted only once; facilitated by a unique numbering system such as the Hogben number or soundex code to identify individuals with precision.

- sex l. inheritance of a trait or a sex chromosome or gonosome. A man receives all his sex-linked genes from his mother and transmits them all to his daughters but not to his sons; a recessive sex-linked character is much more likely to be expressed in the male. SEE ALSO: sex chromosomes, under chromosome.

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link·age 'liŋ-kij n

1) the manner in which atoms or radicals are connected by chemical bonds in a molecule

2) the relationship between genes on the same chromosome that causes them to be inherited together compare MENDEL'S LAW (2)

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n.

(in genetics) the situation in which two or more genes lie close to each other on a chromosome and are therefore very likely to be inherited together. The further two genes are apart the more likely they are to be separated by crossing over during meiosis.

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link·age (lingkґəj) 1. the connection between different atoms in a chemical compound, or the symbol representing it in structural formulas; see also bond. 2. in genetics, the association of genes having loci on the same chromosome, which results in the tendency of a group of such nonallelic genes to be associated in inheritance.