Glossary of Genetic Terminology
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SATELLITES:
Small, round appendages attached by fine stalks to the ends of the short 'p' arms of the acrocentric chromosomes. They do not always stain darkly and may be difficult to
see in a karyotype.
SENSITIVITY:
The ability of a test to detect the presence of a genetic condition or a mutation when it is truly present.
SEX CELLS:
The reproductive cells (sperm or egg) which are the result of meiosis.
SEX CHROMOSOME:
An X or a Y chromosome which are different from the 22 autosomes.
SEX INFLUENCED:
A genetic condition or characteristic whose expression or severity differs between the
sexes. That is, it occurs more frequently in either males or females.
SEX LIMITED:
A genetic condition or characteristic that is expressed in only one sex. That is, it
occurs only in males or in females.
SEX LINKED:
A genetic condition or characteristic which is determined by genes carried on the X or Y chromosomes.
Multiple copies of a short, identical DNA sequence repeated in tandem. The pattern of different numbers of STRs at certain sites on the chromosomes may be used to create a DNA pattern or DNA fingerprint that is as unique as possible for each person.
An inherited blood condition in which the haemoglobin molecule (a type of protein in red blood cells that carries oxygen to the tissues) is abnormal. This produces a severe form of anaemia (see Genetics Fact Sheet 34).
SINGLE NUCLEIOTIDE POLYMORPHISM (SNP):
A DNA sequence variation that involves a change in a single nucleotide. Variations in the genetic code at the level of one nucleotide may be useful in certain applications such as assessing the patterns of inheritance via genetic linkage studies, or forensic DNA testing or DNA fingerprinting.
A large group of genetic conditions in which the bony skeleton develops abnormally. An example of a skeletal dysplasia is achondroplasia (see Genetics Fact Sheet 38).
SOMATIC CELLS:
All the cells of the body except the reproductive cells (sex cells).
SOMATIC GENE THERAPY:
Correcting or transplanting genes that are present in somatic
cells, not the sex cells.
SOMATIC MUTATION:
A change or fault in a gene which is found in the cells of the body but not in the germ or sex cells. Somatic mutations
cannot therefore be passed on to future generations.
SOMATIC STEM CELLS:
Another name for adult stem cells.
SPECIFICITY:
The ability of a test to determine whether a genetic condition or mutation is absent when it is truly absent.
SPERM
(ABBREVIATION OF SPERMATOZOAN):
The male sex cell which contains 23 chromosomes.
It fuses with the egg during fertilisation.
SPORADIC:
A mutation that results in a genetic condition
and which appears for the first time in a family. The mutation takes place in
either the egg or the sperm or at conception.
STEM CELLS:
Undifferentiated cells with the ability to divide for indefinite periods in cell culture and to give rise to specialised, functional cells.
STEREOTYPED BEHAVIOUR:
Repetitive routines or movements that have no function or use.
Any of three mRNA sequences (UGA, UAG, UAA) that do not code for an amino acid and therefore signal that protein production or translation stops.
STORAGE DISEASE:
Any disease or condition which is characterised by the abnormal accumulation and storage of material within the cells. The stored material will vary depending upon the type of condition.
A gene in which if there is a change or mutation, this increases an individual's susceptibility or predisposition to a certain disease or condition. When such a gene change is inherited, there is a greater likelihood that symptoms will develop, but this is not certain.
SYNDROME:
A group of characteristics and/or symptoms that occur together in a recognisable
pattern.
SYNTHESIS:
The process of building a complex compound from a number of simple chemical
elements.