Defining Genetics Terms
 From the April 2002 Disabilities newsletter.
Since the first edition of The Dictionary of Developmental Disabilities Terminology was published in 1996, our knowledge of the human genome and the genetic roots of many developmental disabilities has increased significantly. Clinicians, researchers, and other disability service providers are finding that an understanding of genetics terms is needed in order to navigate journal articles and scientific reports as well as communicate more effectively with the families of the people they serve. We're happy to report that in the about-to-be-published updated version of the dictionary, many genetics terms have been added to help professionals make sense of the new research. For insight into chromosomal structure, genetic testing, and more, see below:
- Acrocentric chromosome — A chromosome with the centromere (typically in the middle) nearer one end; in humans the acrocentric chromosomes (13, 14, 15, 21, and 22) have satellited short arms and stalks that carry genes for ribosomal ribonucleic acid (RNA).
- Chromosome mapping — The methods used to assign genes to specific chromosomes or chromosome regions; includes gene linkage, somatic cell hybrids, and in situ hybridization.
- Genome — The complete deoxyribonucleic acid (DNA) sequence, containing the entire genetic information, of a gamete, an individual, a population, or a species.
- In situ hybridization — Mapping a gene by molecular hybridization of a cloned deoxyribonucleic acid (DNA) sequence, labeled by radioactivity or fluorescence, to a chromosome spread on a slide.
- Locus — The position of a gene in a chromosome.
- Lod score — A statistical method that tests genetic marker data in families to determine whether two loci are linked. The lod score is the logarithm to base 10 of the odds in favor of linkage; by convention, a lod score of 3 (odds of 1000:1 in favor) is taken as proof of linkage, and a lod score of -2 (100:1 against) as proof that the loci are unlinked.
- Preimplantation genetic diagnosis — A procedure involving in vitro fertilization to test cells for the presence or absence of specific genetic defects before the embryo is transferred to the uterus; offered to high-risk patients.
- Uniparental disomy — Both chromosomes in a pair originating from the same parent (e.g., maternal disomy) in contrast to the usual case in which each pair contains one chromosome from each parent. Disomy pairs can contain identical copies of a chromosome from the same parent (termed iso-disomy) or two different chromosomes from the same parent (termed heterodisomy).
  These terms are some of the nearly 200 genetics-related terms added to The Dictionary of Developmental Disabilities Terminology, Second Edition, by Pasquale Accardo and Barbara Whitman. Be sure to check out the on-line version of the dictionary, too!
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