Small portions of DNA within the genome that code for proteins are called genes. They include instructions for our unique qualities, such as eye and hair colour.
A gene is a small segment of DNA that contains the instructions for a particular molecule, typically a protein.
Genes are designed to store information.
Each gene carries the instructions necessary to manufacture the specific proteins required by an organism.
The human genome has 20,687 genes that code for proteins. Alleles are the different versions of genes.
In humans, particular alleles of genes are found in pairs, one on each chromosome (we have 23 pairs of chromosomes). If the alleles of a specific gene are identical, the organism is considered homozygous for that gene. If they are dissimilar, the organism is said to be heterozygous for that gene.
The combination of alleles an individual possesses determines their phenotype.
Several alleles may exist for a gene that determines eye color, for instance. One allele may cause blue eyes, whereas another may cause brown eyes. The final eye colour will depend on which alleles an individual possesses and how they interact.
Sometimes, the trait associated with a particular allele can be dominant or recessive.