Structure and Function of the Genetic Material

Genetics is the study of what genes are, how they carry information, how their information is expressed, and how they are replicated and passed to subsequent generations or other organisms.

DNA in cells exists as a double-stranded helix (see DNA Structure).

A gene is not just a segment of DNA, a gene is a specific sequence of nucleotides that codes for a functional product, usually a protein.

When a gene is expressed (gene expression) the DNA is transcribed to produce mRNA.  The mRNA is then translated into proteins.

The DNA in a cell is duplicated (DNA replication) before the cell divides so each daughter cell receives the same genetic information.

Genotype and Phenotype

Genotype is the genetic composition of an organism - all of its DNA and the genes contained in the DNA.

Phenotype is the result of expression of the genes - the proteins of the cell and the properties they confer on the organism.

DNA and Chromosomes

The DNA in a chromosome exists as one long double helix associated with various proteins that regulate genetic activity.

Bacterial DNA is circular; the chromosome of E. coli, for example, contains about 4 million base pairs and is approximately 1000 times longer that the cell.

Genomics is the molecular characterization of genomes.

A genome is the total of an organism's DNA (and, of course, all of the genes contained in the DNA).

Information contained in an organism's genome is used within a cell when the DNA is transcribed into RNA and translated into proteins.

This information is passed on to later generations when the DNA is replicated and the cell divides.

Information may be passed between cells of the same generation by recombination (more on this later).