The Language of Biology

This section is quite technical, but it will help you to understand that each gene has two parts.

1. The parts on the gene that we use are called coded or exons.


2. The parts on the gene we do not use are called noncoding or introns.

The human genome contains an estimated 20,000-25,000 protein-coding genes, far fewer than had been expected before it's sequencing. In fact, only about 1.5% of the genome codes for proteins, while the rest consists of RNA genes, regulatory sequences, introns and controversially (still active research studying this) "junk" DNA.

Explanation of Image

Image courtesy of the National Cancer Institute

Small coding or used sections of our genes are called "exons". (Pink color in image) Small noncoding or unused sections of our genes are called introns. (Light blue color in image) Chromosomes also have many noncoding gions located outside the genes. These contain large stretches of repetitive sequences.

Some of the sequences in these locations are involved in the regulation of gene expression, and others simply act as spacers. Still other regions have functions as yet undiscovered.

CISN Summary:

1. Coding segments of our genes (exons) make proteins


2. Noncoding segments (introns) do not


3. Noncoding regions make up the bulk of the chromosome


4. Coding genes make up about 2 percent of the total DNA in our genome (make protein). In the human genome, the coding portions of a gene, called exons, are interrupted by intervening sequences, called introns.


5. Over 98 percent of the genome is of unknown function. Although often referred to as "junk" DNA, scientists are beginning to uncover the function of many of these intergenic sequences (introns) found between genes.

Genotype and Phenotype

Cancer may start as a new genotype, that is, as a change in the genetic makeup of a person, but it ultimately produces a new phenotype as well.

		Cancer is known for its everchanging genotypes and phenotypes.
Image courtesy of the National Cancer Institute

 

CISN Summary:

1. The genotype of a person is her or his genetic makeup. It can pertain to all genes or to a specific gene.


2. The phenotype results from the interaction between the genotype and the environment. It is the composite of the characteristics shown by the cell, individual or organism under a particular set of environmental conditions.