Glossary
| Term | Description |
|---|---|
| Background Risk | The empirically derived risk of a given condition or event in the population as a whole. |
| Balanced translocation | A translocation occurs when two or more different chromosomes exchange pieces. It is said to be balanced when no material is either lost or gained during the exchange, and all the genes that make up the exchanged material are still functional. |
| Base Pair | A pair of complementary nucleotide bases, as in double-stranded DNA. Used as the unit of measurement of the length of a DNA sequence. |
| Bases | The molecular building blocks of DNA and RNA. In DNA, adenine (A), thymine (T), guanine (G), and cytosine (C). In RNA, uracil (U) replaces thymine. In DNA, A bonds with T and C bonds with G. In RNA, A bonds with U and C bonds with G. |
| Benign | Not malignant. Having no deleterious affect. |
| Beta chain | One of the two different polypeptide chains of hemoglobin. There are 2 beta chains in each hemoglobin molecule. Beta chains are made up on 146 amino acids. |
| Beta human chorionic gonadotropin | Beta human chorionic gonadotropin (Beta hCG or βhCG) is a hormone produced by the placenta. This hormone can be detected in a pregnant woman’s blood. The first trimester level of beta hCG may be higher in pregnancies in which the baby has Down syndrome. For pregnancies with trisomy 18, the levels of beta hCG may be lower than average.
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| Bifid uvula | The uvula (fleshy mass hanging from the soft palate above the root of the tongue) has two parts or branches. Usually, a uvula has one side, not two. |
| Birth defect | Anomalous or atypical development of some aspect of the body present at birth. |
| BRCA1/BRCA2 | The two genes most commonly associated with hereditary breast and/or ovarian cancer. |