Glossary of Genetic Terminology

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B

BALANCED TRANSLOCATION (RECIPROCAL TRANSLOCATION):
Please see 'Translocation'.

BANDING:
A series of darkly and lightly stained stripes across a chromosome are produced by treating the chromosomes with different chemicals. There are a number of different staining techniques which produce different patterns eg. G-banding, R-banding etc.

BARR BODY:
The sex chromatin or highly condensed inactive X chromosome present in each somatic cell in females (see Genetics Fact Sheet 14).

BASE PAIR:
Two complementary basic building blocks (nucleotide bases) that make up the genetic code, combine to form one rung of the DNA ladder.

BASES:
Also known as nucleotides, they are the basic components of DNA. They are denoted by the letters A (Adenine), G (Guanine), C (Cytosine) and T (Thymine). The sequence of these bases forms the genetic code.

BECKER MUSCULAR DYSTROPHY (BMD):
Is a genetic muscle condition usually affecting boys. Symptoms usually start in adolescence or adulthood and progress slowly but will affect all voluntary muscles.It is characterised by generalised weakness and muscle wasting that affects limb and trunk muscles first. Similar to Duchenne muscular dystrophy but less severe (see Genetics Fact Sheet 41).

BLASTOCYST:
A 5-6 day old embryo, ready for implantation to occur. The blastocyst consists of a sphere made up of an outer layer of cells (the trophectoderm), a fluid-filled cavity (the blastocoel), and a cluster of cells on the interior (the inner cell mass).

BONE MARROW STEM CELLS:
Stem cells found in bone marrow that generate bone, cartilage, fat, and fibrous connective tissue.