| NAA | N-acetyl aspartate; naphthaleneacetic acid; neutral amino acid; neutron activation analysis; neutrop... |
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| Y-linkage | The state of a genetic factor (gene) being borne on the Y chromosome. This idea is analogous with X-linkage but since the Y chromosome does not fully take part in chiasma formation and recombination, it not amenable to analysis by conventional linkage methods. Little is known about its content. There is a gene for the H-Y antigen, and indirect arguments suggest that there is a principle that determines the formation of the testis and masculinization of the foetus but its localization, though narrowing the limits, remains elusive. (05 Mar 2000) |
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| linkage | <genetics> Tendency for two or more non-allelic genes to be inherited together, because they are located more or less closely on the same chromosome. Thus parental combinations of characters are found more frequently in offspring than nonparental. Linkage is measured by the percentage recombination between loci. (04 Jul 1999) |
| linkage analysis | <genetics> Study aimed at establishing linkage between genes. Today linkage analysis serves as a way of gene-hunting and genetic testing. (12 Dec 1998) |
| linkage disequilibrium | <genetics> The occurrence of some genes together, more often than would be expected. Thus, in the HLA system of histocompatibility antigens, HLA A1 is commonly associated with B8 and DR3 and A2 with B7 and DR2, presumably because the combination confers some selective advantage. (18 Nov 1997) |
| linkage equilibrium | <genetics> Situation that should exist in a population undisturbed by selection, migration, etc., in which all possible combinations of linked genes should be present at equal frequency. The situation is no more common than are such undisturbed populations. (18 Nov 1997) |
| linkage group | A set of two or more loci that have been shown by linkage analysis to be physically close in the genome but that have not yet been assigned to specific chromosomes. It is rapidly becoming an outmoded term. (05 Mar 2000) |
| linkage map | <genetics> A map of the relative positions of genetic loci on a chromosome, determined onthe basis of how often the loci are inherited together. Distance ismeasured in centimorgans (cM). (09 Oct 1997) |
| linkage marker | A locus at which there is a high probability of heterozygotes (indispensible state for linkage analysis), but in itself perhaps of no clinical interest. See: marker locus. (05 Mar 2000) |