DNA structure

DNA is the chemical that makes up the genetic material in a cell nucleus. In the nucleus, DNA is contained in structures called chromosomes.

A DNA molecule consists of two long strands that twist around each other to form a double helix. Each strand is a chain of repeating units called nucleotides. A long molecule made from repeating units is called a polymer, so DNA is a polymer.

Human genome research in medicine

An organism’s genome is all of its genetic material. In humans, it includes genes as well as DNA that does not form part of genes. A gene is a section of DNA that contains information for making a functional product, often a protein.

The human genome has been studied as a whole. This provides a basis for investigating whether particular versions of genes are linked to particular diseases. Researchers can compare genetic information from people with and without a disease to look for such links. A link alone does not prove that a gene causes the disease, so further investigation is needed.

Identifying a gene linked to an inherited disorder can help explain how the disorder arises. For example, an inherited change in a gene may alter the protein it produces, affecting how cells function. Understanding this connection can help researchers develop treatments that address the effects of the genetic change.

Genes

A gene is a small section of DNA on a chromosome. The DNA in a gene contains a sequence of bases. The order of these bases provides the information for the order in which amino acids are joined.

Amino acids are the building blocks of proteins. When they are joined in the order specified by a gene, they form a specific protein. Different base sequences can specify different amino acid sequences, producing different proteins.

Tracing human migration using DNA

People inherit DNA from their ancestors. Over generations, different forms of DNA sequences, called genetic variants, can be passed down through populations. People who share variants may have inherited them from common ancestors, so these variants can provide evidence of shared ancestry.

Researchers compare genetic variants in populations from different geographical regions. If populations share a pattern of variants, this can suggest that their ancestors were connected. Researchers also examine where the variants are found: as ancestral groups moved to new regions and had descendants there, they carried variants with them.

By comparing shared variants and their geographical distribution, researchers can infer how ancestral populations may have moved and become related. These patterns are evidence of past migration, rather than a direct record of the exact journeys individuals made.