Genetic and Medical Glossary

Glossary

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There are 23 names in this directory beginning with the letter R.
Radio-ulnar synostosis
abnormal connection between the radius and ulna, the two bones of the forearm

Ray, absent
absence of all phalanges of a digit and the associated metacarpal/metatarsal

Reading frame
refers to the manner in which a messenger RNA (mRNA) sequence is interpreted as a series of amino acid codons by the ribosome; because of the triplet nature of the genetic code, a typical messenger RNA (mRNA) molecule has three possible reading frames, although usually only one of these will actually code for a functional protein

Recessive
a term referring to an allele or trait that will only be expressed if another, dominant, trait or allele is not also present

Reciprocal deletion
recombination products of crossing-over are a duplication at the site of the exchange and a reciprocal deletion

Reciprocal translocation
a two-way exchange of genetic material between two nonhomologous chromosomes, resulting in a wide variety of genetic problems depending on which chromosomes are involved in the translocation

Recombination
formation of new set of alleles on a single chromosome that is not the same as either parent owing to a crossover during meiosis

Renal
of the kidneys

Renal agenesis
absence of one or both kidneys

Rethore syndrome (trisomy 9p)
characterized by cognitive impairment, distinctive malformations of the skull and facial (craniofacial) region, skeletal defects, and structural malformations of the heart; caused by duplication of the short arm (p) of chromosome 9

Retinitis pigmentosa
group of inherited vision disorders that cause progressive degeneration of the retina, the light sensitive membrane that coats the inside of the eyes; may be associated with deafness, obesity, kidney disease, central nervous system and metabolic disorders, and occasionally chromosomal abnormalities

Retinoblastoma
malignant tumor that develops in the nerve-rich layers that line the back of the eyes (retina)

Retrognathia
posteriorly positioned lower jaw, which is set back from the plane of the face when viewed from the side but not from the front; may be accompanied by micrognathia

Reverse transcription polymerase chain reaction (RT-PCR)
a technique, requiring isolated RNA, for quickly determining if a gene or a small set of genes are transcribed in a population of cell

Rhizomelic
disproportion in the length of the most proximal segment of the limbs (upper arms and thighs)

Ribonucleic acid (RNA)
a form of nucleic acid in the cell used primarily for genetic expression through transcription and translation; in structure, it is virtually identical to DNA, except that ribose is used as the sugar in each nucleotide and the nitrogenous base thymine is replaced by uracil; present in three major forms in the cell: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)

Rieger syndrome
genetic disorder characterized by absent or underdeveloped (hypodontia or partial adontia) teeth, mild craniofacial abnormalities, and various abnormalities of the eye, especially glaucoma

Ring chromosome
occurs as a result of the fusion of the two ends of the same chromosome; there is a consequent loss of genetic material

Ritscher–Schinzel syndrome (craniocerebellocardiac dysplasia)
characterized by heart defects, cerebellar hypoplasia, and cranial dysmorphism; autosomal recessive disease caused by mutation on the long arm (q) of chromosome 8 at 8q24

Robertsonian translocation
type of translocation exclusive to the acrocentric chromosomes (13, 14, 15, 21 and 22) in which two of these chromosomes join at or near their centromeres, constituting a fusion between two whole chromosomes

Rocker bottom feet
presence of both a ‘prominent heel’ and a ‘convex contour of the sole’

Rubinstein–Taybi syndrome
multisystem disorder characterized by growth retardation and delayed bone age, developmental and psycho-motor delays, cognitive impairment, distinctive abnormalities of the head and face (craniofacial dysmorphism), and/or breathing and swallowing difficulties; many may have malformations of the heart, kidneys, urogenital system, and/or skeletal system; gene responsible is located on the short arm (p) of chromosome 16 at 16p13.3

Russell -Silver syndrome
disorder characterized by prenatal and postnatal growth retardation, large forehead that protrudes out from the plane of the face, triangular-shaped face, pinky that is fixed or "locked" in a bent position (clinodactyly), lack of appetite/low BMI, and undergrowth of one side or limb(s) of the body (hemihypotrophy), resulting in unequal (asymmetric) growth; heterogeneous, but believed to be caused by abnormalities certain genes on chromosomes 7 or 11

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