Key Definitions

Allele

The particular form of a gene, sequence or a base.

Base

One of 4 molecules that hold the 2 strands of DNA in a chromosome together. The sequence of the bases in a gene determine the structure of proteins.

Chromosome:

A package of DNA. The largest package is chromosome 1, the smallest is chromosome 22.

Diplotype

The two allelic forms of a gene, sequence or base found on the maternal and paternal DNA strands.

DNA

Deoxyribonucleic acid. A collection of bases and connecting sugar molecules that are organized into genes, which specify the exact composition of proteins. DNA is species specific and is common to all life.

Gene

A segment of DNA that specifies the composition of a protein.

Genome

The complete set of DNA found in all 23 chromosomes (in humans). Each species has its own genome.

Genotype

The identity of a base at a single site (ie, G, A, T or C).

GWAS

Genome Wide Association Study. A research study attempting to correlate a disease, or characteristic with any of the known sites of DNA variation.

Haplotype

The collection of DNA variation found on the same strand of DNA (ie, on one chromosome). A haplotype may be restricted to a short sequence or to an entire chromosome.

Linkage Disequilibrium 

The tendency of DNA segments to be inherited with others that are located close by. The farther apart DNA segments on the same chromosomal strand are from one another, the greater the likelihood that they will become separated from one another during cell division. Two DNA markers that are always inherited together are said to be in "absolute linkage disequilibrium".

Mutation

An induced alteration in the ancestral DNA sequence.

Nucleotide

The chemical description of the bases that make up DNA.

Purines

A DNA base chemical group that contains the double ringed guanine and adenine.

Pyrimidines

A DNA base chemical group that contains the single ringed thymine and adenine.

SNP

A Single Nucleotide Polymorphism is a specific site of naturally occurring variation in the human genome that has been inherited over many generations. By convention, if the variation is found in more than 1% of the time it is called a "SNP," if it is found less frequently it is called a "mutation."