Gene

Genesare parts ofDNA.DNA is amoleculeinside acellthat carries the instructions for making theproteinsthe cell will need. Each gene contains a single set of instructions. These instructions usuallycodefor a particular protein. Humans have about 20,000 genes that code proteins and many more that are non-coding. Half of a person's genes come from the mother. The other half come from the father.

The definition

Originally: a hereditary unit which occupies a specific position (locus) on achromosome.Other definitions are ways the gene showed itself:

1. A unit which has one or more specific effects on thephenotypeof an organism;

2. A unit that canmutateto variousalleles;

3. A unit whichrecombineswith other such units.

Modern definitions must take note of later discoveries.There are now two classes of genes:^p173

1. genes that aretranscribedintoRNAsand aretranslatedintopolypeptidechains.

2. genes whose transcripts (tRNAs,rRNAs,snRNAs) are used directly. These are operators which serve as 'regulatory sequences' during transcription and translation of the DNA. "The building blocks of life."

What genes do?

Genes are passed on fromparentto child and are an important part of what decides how children look and act (theirbiological properties). Genes affect the way our bodies work, including how we look. Our eye, hair and skin color are decided by genes. It is said that genes causegeneticeffects in our bodies.

A gene may bedominantorrecessive.These terms refer to the effect a gene has on the offspring who carry it in theirgenome.

For example, let's say a mother only has genes for brown hair and a father only has genes for red hair. The child willinherit– receive – genes for red hair (from her father) and brown hair (from her mother). The brown hair gene is 'dominant' to the red hair gene. This means the child will have brown hair even though she has genes for both red and brown hair. This means only one dominant gene is needed for the child to receive that particular trait, while two recessive genes are needed for one.

A recessivetraitmight stay hidden for manygenerations.Let us use the child from the last example. We will call her "Mary". Mary has brown hair but has genes for both red and brown hair. Let us say Mary grew up and married Tom. Tom also has brown hair, but like Mary one of his parents had red hair. This means Tom has genes for both red and brown hair. Mary and Tom would each have a chance of passing either brown or red hair genes to their children. This means that the children of Mary and Tom could have either red or brown hair. This explains why a person might look different from their parents, but look like theirgrandparentsor great-grandparents.

Structure and function

The structure of a gene has many elements: the actual protein coding sequence is only a small part. There are DNA regions that are not transcribed as well as untranslated regions of the RNA.

The structure of a eukaryotic protein-coding gene.

Related pages

• Allele#Dominance
• Sequence analysis
• Genetics
• ENCODE,the complete analysis of the human genome
• Gene therapy
• Genetic disorder