Glossary

1994 Woodrow Wilson Biology Institute

A quick reference supplement to the Drosophila Unit

Amino acid - Any of 20 basic building blocks of proteins composed of a free amino (NH2) end, a free carboxyl (COOH) end, and a side group (R)

Antennapedia - A homeotic mutation of Drosophila, where a pair of legs replaces the antenna

Autosome - A chromosome that is not involved in sex determination

Base pair - A pair of complementary nitrogenous bases in a DNA molecule-adenine-thymine and guanine-cytosine. Also, the unit of measurement for DNA sequences

Biotechnology - The scientific manipulation of living organisms, especially at the molecular genetic level, to produce useful products

Bithorax - Homeotic mutations of Drosophila that lead to development of a second pair of partial or complete wings

Centromere - The central portion of the chromosome to which the spindle fibers attach during mitotic and meiotic division

Chromatid - Each of the two daughter strands of a duplicated chromosome joined at the centromere during mitosis and meiosis

Chromosomes - A single DNA molecule, condensed into a compact structure in vivo by complexing with accessory histones or histone-like proteins.

Chromosomes exist as homologous pairs in higher eukaryotes

Cloning - The mitotic division of a progenitor cell to give rise to a population of identical daughter cells or clones

Crossing-over - The exchange of DNA sequences between chromatids of homologous chromosomes during meiosis

Diploid - The condition when the genome of an organism consists of two copies of each chromosome

DNA(deoxyribonucleic acid) - An organic acid and polymer composed of four nitrogenous bases- adenine, thymine, cytosine, and guanine. DNA is the genetic material of most organisms and exists as a double-stranded molecule in which two anti parallel strands are held together by hydrogen bonds between adenine-thymine and cytosine-guanine

DNA polymorphism - One of two or more alternate forms (alleles) of a chromosomal locus that differ in nucleotide sequence or have variable numbers of repeated nucleotide units

Double helix - Describes the coiling of the anti parallel strands of the DNA molecule, resembling a spiral staircase in which the paired bases form the steps and the sugar-phosphate backbones form the rails

Drosophila melanogaster - The fruit fly whose common use in genetic studies was introduced by Thomas Hunt Morgan in the early 1900's

Electrophoresis - The technique of separating charged molecules in a matrix to which is applied an electrical field

Eukaryote - An organism whose cells possess a nucleus and other membrane-bound vesicles, including all members of the protist, fungi, plant, and animal kingdoms

Evolution - The long-term process through which a population of organisms accumulates genetic changes that enable its members to successfully adapt to environmental conditions and to better exploit food resources

Gamete - A haploid sex cell, egg or sperm, that contains a single copy of each chromosome

Gene - A locus on a chromosome that encodes a specific protein or several related proteins

Genetic engineering - The manipulation of an organism's endowment by introducing or eliminating specific genes; a broad definition of genetic engineering also includes selective breeding and other means of artificial selection

Genetic (linkage) map - A linear map of the relative positions of genes along a chromosome. Distances are established by linkage analysis which determines the frequency at which two gene loci become separated during chromosomal recombination

Genome - The genetic complement contained in the chromosomes of a given organism, usually the haploid chromosome state

Genotype - The structure of DNA that determines the expression of a trait (phenotype)

Germ Cell - (germ line) Gametes and the progenitor tissues from which they are derived

Haploid - The chromosome number equal to one complete set of the genetic endowment of a eukaryotic organism

Histone - Any of five related proteins, composed primarily of basic amino acids, which are the scaffold around which DNA is wound to form the chromatin structure of eukaryotic chromosomes

Homeotic mutation - Any mutation that disrupts a developmental pathway involved in determining spatial relationships of tissues and body parts

Homolog - Any member of a set of genes or DNA sequences from different organisms whose nucleotide sequences show a high degree of one to one correspondence

Human Genome Project - A project coordinated by the National Institutes of Health(NIH) and the Dept. of Energy (DOE) to determine the entire nucleotide sequence of the human chromosomes

Hybrid - The offspring of two parents differing in at least one genetic characteristic (trait). Also, heteroduplex DNA or DNA-RNA molecule

Hybridization - The hydrogen bonding of complementary DNA and /or RNA sequences to form a duplex molecule

Inbreed - To mate closely related individuals

In vivo - Refers to biological processes that take place within a living organism or cell

Locus (plural, loci) - A specific location or site on a chromosome

Meiosis - The reduction division process by which haploid gametes and spores are formed, consisting of a single duplication of the genetic material followed by two mitotic divisions

Mitosis - The replication of a cell to form two daughter cells with identical sets of chromosomes

Mutation - An alteration in DNA structure or sequence of a gene

Natural selection - The differential survival and reproduction of organisms with genetic characteristics that enable them to better utilize environmental resources

Nitrogenous bases - The purines (adenine and guanine) and pyrimidines (thymine, cytosine, and uracil) that comprise DNA and RNA molecules

Pedigree - A diagram mapping the genetic history or a particular family

Phenotype - The expression of gene alleles (genotype) as a detectable physical or biochemical trait

Protein - A polymer of amino acids linked via peptide bonds and which may be composed of two or more polypeptide chains

Somatic cell - Any nongerm cell that composes the body of an organism and which possesses a set of multiploid chromosomes

Species - A classification of related organisms that can freely interbreed

Transcription - The process of creating a complementary RNA copy of DNA

Transduction - The transfer of DNA sequences from one bacterium to another via lysogenic infection by a bacteriophage (transducing phage)

Translation - The process of converting the genetic information of an mRNA on ribosomes into a polypeptide. Transfer RNA molecules carry the appropriate amino acids to the ribosome, where they are joined by peptide bonds

Translocation - The movement or reciprocal exchange of large chromosomal segments, typically between two different chromosomes

X-linked disease - A genetic disease caused by a mutation on the X chromosome. In X-linked recessive conditions, a normal female "carrier" passes on the mutated X chromosome to an affected son

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