A relatively very common and medically significant type of chromosome rearrangement that is formed by fusion of the whole long arms of two acrocentric chromosomes (chromosomes with the centromere near the very end). One in about 900 babies is born with a Robertsonian translocation making it the most common kind of chromosome rearrangement known in people. All five of the acrocentric chromosomes in people — chromosome numbers 13, 14, 15, 21 and 22 — have been found to engage in Robertsonian translocations. However, the formation of Robertsonian translocations was discovered by Hecht and coworkers to be highly nonrandom. Far and away the most frequent forms of Robersonian translocations are between chromosomes 13 and 14, between 13 and 21, and between 21 and 22.
In balanced form, a Robertsonian translocation takes the place of two acrocentric chromosomes and results in no problems for the person carrying it. But in unbalanced form, Robertsonian translocations produce chromosome imbalance and cause syndrome of multiple malformations and mental retardation. Robertsonian translocations between chromosomes 13 and 14 lead to the trisomy 13 (Patau) syndrome. And the Robertsonian translocations between 14 and 21 and between 21 and 22 can and do result in (trisomy 21 (Down) syndrome.
Robertsonian translocations are named for the America insect geneticist W.R.B. Robertson who first described this form of translocation (in grasshoppers) in 1916 and are also known as whole-arm or centric-fusion translocations or rearrangements.
- Transmissible spongiform encephalopathy
kuru; Creutzfeldt-Jakob disease; Gerstmann-Straussler syndrome; fatal familial insomnia; variant Creutzfeldt-Jakob disease (vCJD).
- Transmission distortion
meiotic drive which is preferential selection during meiosis (germ cell production); gametic selection which is preferential selection of gametes (germ cells) ; and postzygotic viability which reflects differences in the ability of conceptions to survive. All of these mechanisms for selection result in the production of offspring in proportions that deviate from Mendelian predictions. For […]
- Transmission, perinatal
Transmission of a disease-causing agent (a pathogen) from mother to baby during the perinatal period, the period immediately before and after birth. The perinatal period is defined in diverse ways. Depending on the definition, it starts at the 20th to 28th week of gestation and ends 1 to 4 weeks after birth. The perinatally transmitted […]
- Transmission, vertical
Passage of a disease-causing agent (pathogen) from mother to baby during the period immediately before and after birth. Transmission might occur across the placenta, in the breast milk, or through direct contact during or after birth. For example, HIV can be a vertically transmitted pathogen. Also known as perinatal transmission.
- Transmyocardial laser revascularization
A procedure by which a physician uses a laser to make holes in the heart to relieve the pain of severe angina. Transmyocardial laser revascularization has been done from both the outside and inside of the heart. When done from the outside, a laser (carbon dioxide or holmium laser) is placed in proximity to the […]