Genes:The basic biological units ofheredity. Segments ofdeoxyribonucleic acid(DNA) needed to contribute to a function.
An official definition:According to the official Guidelines for HumanGeneNomenclature, a gene is defined as "a DNA segment that contributes tophenotype/function.Inthe absence of demonstrated function a gene may be characterized by sequence,转录or homology."
背景:Genesare composed of DNA, amolecule在难忘的形状of adouble helix, a spiral ladder. Each rung of the spiral ladder consists of two paired chemicals called bases. There are four types of bases. They areadenine(A),thymine(T),cytosine(C), andguanine(G). As indicated, each base is symbolized by the first letter of its name: A, T, C, and G. Certain bases always pair together (AT and GC). Different sequences of base pairs form coded messages.
The gene:A gene is a sequence (a string) of bases. It is made up of combinations of A, T, C, and G. These unique combinations determine the gene's function, much as letters join together to form words. Each person has thousands of genes -- billions of base pairs of DNA or bits of information repeated in thenucleiof human cells --which determine individual chacteristics (genetictraits).
Thechromosome:Genes are arranged in precise arrays all along the length of 23 pairs of much larger structures: thechromosomes. One chromosome in each pair comes from themotherand the other one from thefather. The chromosomes in any particular pair look like each other, except in a boy. There is one pair of chromosomes, which usually settles the sex of the individual. This pair has two X chromosomes in females and one X and oneY chromosomein males.
The X and Y chromosomes:These chromosomes -- the X and Y are always capitalized -- are the sex chromosomes. All the other chromosomes in the humanchromosome complementare numbered from 1 to 22 and are called the autosomes (literally, the other chromosomes).
History of the gene: 1869-1970:
- 1869 - The chemical material DNA is discovered in cells but its real functions are not known.
- 1909 -The term "gene" is first usedand the chemical composition of DNA is discovered.
- 1920 - Chromosomes are proposed as the mechanism by which inherited characteristics are passed on.
- 1944 - DNA is first connected to theinheritanceof traits.
- 1951 - The firstsharpX-raydiffraction photographs of DNA are obtained.
- 1953 -CrickandWatsondescribe the structure of DNA.
- 1956 - DNA is made artificially.
- 1966 - DNA is found to be present not only in chromosomes but also in themitochondria.
- 1969 - The first single gene is isolated.
- 1970 - The first artificial gene is made.
