X-linked gene

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one of the biologic units of heredity, self-reproducing, and located at a definite position (locus) on a particular chromosome. Genes make up segments of the complex deoxyribonucleic acid (DNA) molecule that controls cellular reproduction and function. There are thousands of genes in the chromosomes of each cell nucleus; they play an important role in heredity because they control the individual physical, biochemical, and physiologic traits inherited by offspring from their parents. Through the genetic code of DNA they also control the day-to-day functions and reproduction of all cells in the body. For example, the genes control the synthesis of structural proteins and also the enzymes that regulate various chemical reactions that take place in a cell.

The gene is capable of replication. When a cell multiplies by mitosis each daughter cell carries a set of genes that is an exact replica of that of the parent cell. This characteristic of replication explains how genes can carry hereditary traits through successive generations without change.
allelic gene allele.
complementary g's two independent pairs of nonallelic genes, neither of which will produce its effect in the absence of the other.
DCC gene (deleted in colorectal carcinoma) a gene normally expressed in the mucosa of the colon but reduced or absent in a small proportion of patients with colorectal cancer.
dominant gene one that produces an effect (the phenotype) in the organism regardless of the state of the corresponding allele. An example of a trait determined by a dominant gene is brown eye color. See also heredity.
histocompatibility gene one that determines the specificity of tissue antigenicity (hla antigens) and thus the compatibility of donor and recipient in tissue transplantation and blood transfusion.
holandric g's genes located on the Y chromosome and appearing only in male offspring.
immune response (Ir) g's genes of the major histocompatibility complex that govern the immune response to individual immunogens.
immune suppressor (Is) g's genes that govern the formation of suppressor T lymphocytes.
immunoglobulin g's the genes coding for immunoglobulin heavy and light chains, which are organized in three loci coding for κ light chains, λ light chains, and heavy chains.
K-ras gene a type of oncogene.
lethal gene one whose presence brings about the death of the organism or permits survival only under certain conditions.
major gene a gene whose effect on the phenotype is always evident, regardless of how this effect is modified by other genes.
mutant gene one that has undergone a detectable mutation.
operator gene one serving as a starting point for reading the genetic code, and which, through interaction with a repressor, controls the activity of structural genes associated with it in the operon.
gene pool all of the genes possessed by all of the members of a population that will reproduce.
recessive gene one that produces an effect in the organism only when it is transmitted by both parents, i.e., only when the individual is homozygous. See also heredity.
regulator gene (repressor gene) one that synthesizes repressor, a substance which, through interaction with the operator gene, switches off the activity of the structural genes associated with it in the operon.
sex-linked gene a gene carried on a sex chromosome (X or Y); only X linkage has clinical significance. See X-linked gene.
structural gene one that forms templates for messenger RNA and is thereby responsible for the amino acid sequence of specific polypeptides.
tumor suppressor gene a gene whose function is to limit cell proliferation and loss of whose function leads to cell transformation and tumor growth; called also antioncogene.
X-linked gene a gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. the term “X-linked” is sometimes used synonymously with “sex-linked,” since no genetic disorders have as yet been associated with genes on the Y chromosome.

X-linked gene

a gene located on an X chromosome.

X-linked gene

a gene carried on the X chromosome; the corresponding trait, whether dominant or recessive, is always expressed in males, who have only one X chromosome. The term "X-linked" is sometimes used synonymously with "sex-linked," because no genetic disorders have as yet been associated with genes on the Y chromosome.

X-link·ed gene

(lingkt jēn)
A gene located on an X chromosome.

X-linked gene

A gene carried on the X chromosome, one of the two sex chromosomes.
Mentioned in: Mucopolysaccharidoses
References in periodicals archive ?
Detection of carriers of X-linked gene for Duchenne muscular dystrophy by levels of creatine kinase and pyruvate kinase.
5) clearly showed that the peak areas of the amplification products for the normal female are about double those for the normal male, as expected for an X-linked gene.
Furthermore, I will study the dynamics of the expression of X-linked genes in conjunction with chromatin changes in PGCs by monitoring the loss of H3K27me3 enrichment on the inactive X chromosome.
1) In females, lyonization results in functional mosaicism of X-linked genes, which is manifested by the Blaschkoid distribution of cutaneous lesions.
Such methylation-driven silencing is at the root, for instance, of X-chromosome inactivation, the dosage compensation activity which occurs in female autosomal cells whereby one X chromosome is shut down, giving male (XY) and female (XX) cells effectively equal expression bases for X-linked genes.
Mental retardation/intellectual disability is more common in males than in females, therefore it had been assumed that mutations in X-linked genes are responsible for up to 25% of MR cases but data suggest that X-linked genes contribute to only 10% of cases with MR.
Thus, the hypothesis suggesting that most female monozygotic twins are likely to be discordant in the differential expression of their X-linked genes remains logical and experimentally supported [Singh et al.
This concept, according to which inferiority of the oocyte is already determined before fertilization, in combination with the deleterious sublethal X-linked genes [in males not compensated for by a second X-chromosome with normal genes (21)] explains the male sex-specific loss of conceptuses, particularly when already affected and following a dose-response gradient.
There are several known X-linked disorders that lead to mental retardation (Neri, Chiurazzi, Arena, & Lubs, 1994), a fact that leads to the question of whether normal variation in any of the associated X-linked genes contribute to the variation in intelligence observed in the general population.

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