translocation

translocation /trans·lo·ca·tion/ (trans″lo-ka´shun) the attachment of a fragment of one chromosome to a nonhomologous chromosome. Abbreviated t.

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reciprocal translocation  the complete exchange of fragments between two broken nonhomologous chromosomes, one part of one uniting with part of the other, with no fragments left over. Abbreviated rcp.

robertsonian translocation  translocation involving two acrocentric chromosomes, which fuse at the centromere region and lose their short arms.

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trans·lo·ca·tion (trnsl-kshn, trnz-)

n.

Transposition of two segments between nonhomologous chromosomes as a result of abnormal breakage and refusion of reciprocal segments.

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Translocation

The transfer of one part of a chromosome to another chromosome during cell division. A balanced translocation occurs when pieces from two different chromosomes exchange places without loss or gain of any chromosome material. An unbalanced translocation involves the unequal loss or gain of genetic information between two chromosomes.

Mentioned in: Down Syndrome, Patau Syndrome, Prader-Willi Syndrome

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translocation

[-lōkā′shən]

Etymology: L, trans + locus, place

the rearrangement of DNA within a chromosome or the transfer of a segment of one chromosome to a nonhomologous one. In simple translocations, an end segment of one chromosome is transferred onto the end of another, involving a single break in only one of the chromosomes. Translocations in which material from the middle of one chromosome is shifted to the middle of another one are more complex and involve at least three breaks in the participating chromosomes. Such shifting of genetic material can result in serious disorders, such as Down syndrome, which can be caused by a 14/21 translocation, and chronic granulocytic leukemia, in which part of the long arm of chromosome 22 is translocated to the short arm of chromosome 9. Kinds of translocations are balanced translocation, reciprocal translocation, and robertsonian translocation.

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translocation,

n the rearrangement of genetic material within the same chromosome or the transfer of a segment of one chromosome to another nonhomologous one.

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translocation

the attachment of a fragment of one chromosome to a nonhomologous chromosome. See also chromosomal abnormality. The translocations recorded include adjacent section, alternate segregation, centric fusion, distal segment, eye color, heterozygote, interstitial segment, reciprocal, Robertsonian.

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Robertsonian translocation

that in which the breaks occur at the centromeres and entire chromosome arms are exchanged, usually involving two acrocentric chromosomes.

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chromosome 

One of the thread-like structures located within the cell nucleus composed of an extremely long, double-stranded DNA (deoxyribonucleic acid) helix tightly folded around proteins called histones. Each chromosome carries genes that contain the hereditary material that controls the growth and characteristics of the body. There are 46 chromosomes in each human somatic cell organized in 23 pairs, of which 22 pairs are similar in appearance but differ at the molecular level. They are called autosomal chromosomes or autosomes and are designated by a number (with chromosome 1 being the longest, followed by chromosome 2, etc.). The other pair, the sex chromosomes determines the sex of the individual. In mammals the two sex chromosomes of females are alike (homologous) and are referred to as X chromosomes. Males carry one X chromosome along with a much shorter chromosome, the Y chromosome. Each chromosome has a centromere that divides it into two arms, the short arm 'p' and the long arm 'q'. Disorders of chromosome number in which the number of chromosomes is above or below the normal (46) are called aneuploidy. Common forms of aneuploidy are trisomy in which there is one extra chromosome and monosomy in which there is one less, than the normal 46. They rarely cause specific eye diseases but affected individuals present ocular manifestations. Examples: Down's syndrome (trisomy of chromosome 21), Edwards' syndrome (trisomy 18), Turner's syndrome (monosomy 45 XO). There are other chromosome abnormalities such as translocation (one segment of a chromosome is transferred to another chromosome) as may occur in congenital anterior polar cataract, deletion (a loss of a piece of chromosome) as in aniridia, choroideremia, retinoblastoma, etc. Other cases involve damage of a chromosome (e.g. fragile X syndrome). See defective colour vision; gene; mitosis; mutation.

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mutation

A permanent transmissible change in the nucleotide sequence of the DNA within a gene, or a change in the physical structure of a chromosome. It can occur by substitution (one base or nucleotide is replaced by another), transition (a purine (adenine or guanine) is replaced by another purine or one pyrimidine (cytosine or thymine) is replaced by another pyrimidine), transversion (a pyrimidine is replaced by a purine or vice versa), deletion or insertion of one or more bases. Mutations can also occur in a chromosome as a result of inversion (a segment of chromosome is inserted in reverse order), deletion (a loss of a piece of chromosome) or translocation (a piece of chromosome attaches to another). Mutations result in the formation of a protein with an abnormal amino acid or an absence of the protein and these may result in disease but some mutations may be beneficial. Mutations may be caused by copying errors in the genetic material during cell division, by exposure to ultraviolet or ionizing radiation (X-rays, gamma rays), carcinogens, viruses, or spontaneously. See chromosome; gene.