Glossary of Scientific Terms

R

Recessive trait
The quality of a gene or allele regarding its ability to express a phenotype. A recessive allele can only express its phenotype if both copies in a diploid organisms are identical. Often, a recessive allele is matched with a dominant allele, which overrides the activity of the recessive one. In this case, the effect of the gene cannot be seen, but it can still be inherited. These are important considerations in genetic diseases that are often caused by defective copies of a gene (allele) that cause the disease only, if both copies of the gene are defective (homozygous for the recessive allele). Heterozygous individuals with a healthy allele do not suffer the disease but are carriers. Examples of recessive genetic diseases are cystic fibrosis and hypercholesterolemia.

Redundancy
Reduncancy in biology is an important hallmark of the complexity and robustness of life. Redundancy usually means that different parts of a cell or organism can carry out the same function. This way, a defective part is not damaging to the cell. Redundancy also allows evolution of diversity, because a particular structure may mutate (change) and adopt a new function. The loss of the old function is taken over by another part of the cell or organism.

Replication, of DNA
The replication of DNA is a fundamental process during cell division that provides the two daughter cells (offspring) with identical sets of genes. The replication requires the temporary separation of the DNA double helix into single strand forms where each of the two strands serves as a molecular template for the synthesis of one new complementary strand to form two new double helical copies of the original DNA. The accuracy of replication is based on the specific molecular interaction between two of the four existing nucleotides (A adenine; T thymine; G guanine; C cytosine) to form only AT or GC base pairs. Any other pairing can cause mutations in the daughter DNA, a process that occurs very rarely, and is one of the processes leading to genetic diversity of life.

Ribosome
The cellular particles made of protein and RNA subunits that catalyze the synthesis of proteins along a messenger RNA (mRNA) template. This process is called translation that converts a nucleic acid genetic code into an amino acid sequence. The result are proteins (enzymes) with each having a specific structure and function carrying out a particular metabolic reaction in a cell.

RNA
Ribonucleic acid, the most common form of nucleic acid used for storage of chemical energy, processing genetic information from genes (DNA) via messenger RNA (mRNA) into proteins. RNA is one of the most ancient form of molecular structures with enzymatic activity. As a matter of fact, protein biosynthesis is entirely controlled by RNA molecules including mRNA (genetic information), transfer RNA (tRNA) for translating the DNA code into amino acid code, and ribosomal RNA (rRNA) that provide the enzymatic linkage (chemical bond formation) of amino acids into proteins. The use of RNA probably precedes the use of proteins and most modern genomes (except for some viruses) are made of DNA instead of RNA but can only be read by proteins. DNA is the more chemically stable of the two forms of nucleic acids.