GLOSSARY

Acrocentric A chromosome with effectively only a long arm – chromosomes 13,14,15,21, and 22 Allele A genetic variation of a gene or DNA marker Aneuploidy An excess or deficiency of chromosomal material Anti-codon An element of transfer RNA which binds a specific amino acid Autosomal dominant Inheritance pattern characterized by transmission through several generations, male-to-

male transmission, and a 50:50 risk to the children of any affected person. Autosomal recessive Inheritance pattern characterized by several affected members of the same generation,

with carrier parents and a 1:4 recurrence risk where both parents are carriers Base pair Unit of double-stranded DNA Centromere Element of chromosome involved in chromosome replication, found as a constriction in

the chromosome Chromatid Condensed chromosome found just before mitosis Codon Three base pair element of DNA encoding an amino acid Diploid A complement of two copies of each chromosome per cell DNA marker A piece of DNA corresponding to a specific gene or chromosomal segment Enhancers Elements of DNA which are involved in increasing gene transcription Exon A part of a gene which is transcribed into mRNA Expression The way in which a gene fault manifests clinically FISH Fluorescent in situ hybridization – a new and powerful technique for studying specific

chromosomes or regions of chromosomes Gamete A germ cell – sperm or oocyte Genetic imprinting The marking of a gene according to which parent has passed the gene to its child Haploid A complement of one copy of each chromosome per cell (as in sperm or oocyte) Haplotype A pattern of alleles of DNA markers representing one of the two copies of a

chromosomal region Histone A DNA-binding protein important in chromosomal folding Interphase Phase of mitosis in which the chromosomes are very elongated Intron The part of a gene between the exons which is not transcribed into mRNA Isochromosome An abnormal chromosome made up of two long or two short arms of a normal

chromosome Karyotype An analysis of the chromosome complement of a cell type Linkage analysis The use of polymorphic DNA markers to perform gene tracking studies within a family Meiosis The process of cell division to give haploid germ cells Metaphase Phase of mitosis in which the chromosomes are very condensed and easier to analyze Microsatellite marker A DNA marker which detects variation in number of an anonymous small repetitive

element of DNA Minisatellite marker A DNA marker which detects variation in number of an anonymous medium repetitive

element of DNA Mitosis The normal process of cell division to give two diploid copies of a cell Non-dysjunction A failure of meiosis, giving two copies of a chromosome in one gamete, and no copy of a

chromosome in the other gamete Nucleosome The combination of a histone and its bound DNA Oligonucleotide primers Small lengths of synthetic single-stranded DNA of a specific sequence Paracentric inversion A rearrangement of chromosomal material within one arm of a chromosome PCR Polymerase chain reaction – a method of generating large amounts of specific DNA

from a small amount of target sequence Penetrance The number of people known to carry a gene mutation who manifest the condition Pericentric inversion A rearrangement of chromosomal material around the centromere of a chromosome Promoter Element of a gene which is necessary to activate gene transcription Prophase Phase of the cell cycle where condensation of the chromosomes occurs, just before

metaphase

Reciprocal translocation Exchange of chromosomal segments between different chromosomes Restriction enzyme An enzyme which cuts double-stranded DNA at a specific unique short DNA sequence Restriction fragment A genetic variation between two copies of the same gene, where one gene may have one length polymorphism copy of a restriction enzyme recognition site, and the other has two copies. This

variation can be detected using PCR or Southern blotting. Ribosome Area of the cell where mRNA is converted into protein Ring chromosome An abnormal chromosome in which the tips of the long and short arms have fused Robertsonian translocation A fusion of two acrocentric chromosomes Southern blotting A process of immobilizing DNA to nylon membrane for genetic analysis Suppressor A DNA element which reduces the expression of a gene Telophase The last phase of mitosis Telomere The end of a chromosome Transcription The process of converting DNA into mRNA Translation The production of protein from a DNA sequence Triploidy Three of each chromosome, i.e. 69 chromosomes in man Trisomy One extra chromosome, i.e. 47 chromosomes in man X-linked recessive Inheritance characterized by affected males in several generations, and by female carriers

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