Glossary Old

Allele
Variant form of a gene

Autosomes
The 22 pairs of recombining chromosomes in the cell nucleus, which, along with the X and Y sex chromosomes, make up the nuclear genome

Base
The chemical building blocks of DNA. Named A, T, C, and G (adenine, cytosine, thymine, and guanine), these bases pair up to form the “stairs” of the DNA double helix and always combine in the same patterns: A with T and C with G.

Cell
The smallest unit of living matter that can operate independently

Chromosome
Long strands of DNA on which genes are found. Each human cell has 46 chromosomes in 23 pairs. One member of each pair is inherited from the mother, the other from the father.

Darwin, Charles
Charles Darwin’s 1859 book The Origin of Species promoted a theory of evolution by natural selection and challenged Victorian-era ideas about the role of humans in the universe. Darwin’s theories were based on a constantly evolving natural world and held that each generation of a species had to compete for survival. Survivors held some natural advantages over their less fortunate relatives and passed those characteristics on to their progeny, thus over-representing these favored genetic types in the next generation. Darwin also advanced the idea that species were descended from a common ancestor. Darwin’s work became the foundation of modern evolutionary theory.

DNA (Deoxyribonucleic Acid)
The double helix-shaped molecule that holds an organism’s genetic information. DNA is composed of sugars, phosphates, and four nucleotide bases: adenine, guanine, cytosine, and thymine (A, G, C, T). The bases bind together in specific pairs.

Double Helix
The shape of DNA, similar to that of a spiral staircase or twisted ladder. The stairway’s railings are composed of sugars and phosphates. Its sides contain the patterned base pairs: A, T, C, and G. When a cell divides for reproduction, the helix unwinds and splits down the middle like a zipper in order to copy itself.

FOXP2
The first gene to be linked to language production, and one of the keys to the development of brain regions associated with speech. The development of language may be tied to a genetic mutation in FOXP2 that is shared by humans and our cousins, the Neanderthals, implying that it could have occurred more than 500,000 years ago before the ancestors of the Neanderthals migrated out of Africa.

Gene
Segment of DNA that is the basic functional unit of heredity. Genes are determined by an ordered sequence of chemical bases found in a unique position on a specific chromosome. Their “blueprint” guides protein production, which determines how different cells in the body function. Inherited genes also control an animal’s unique set of physical traits.

Genetic Marker
Random mutations in the DNA sequence which act as genetic milestones. Once markers have been identified they can be traced back in time to their origin—the most recent common ancestor of everyone who carries the marker.

Geno Chip
A custom-designed genotyping array composed of nearly 150,000 microscopic beads, each of which tests for a different genetic marker on the autosomes, Y-chromosome, and mtDNA

Genome
The total DNA sequence that serves as an instruction manual for all proteins created in your body. Two copies of the genome are found inside each of our cells.

Haplogroup
Branches on the trees of early human migrations and genetic evolution, haplogroups often have a geographic relation. Haplogroups are defined by genetic mutations or “markers” found in Y-chromosome and mtDNA testing. These markers link the members of a haplogroup back to the marker’s first appearance in the group’s common ancestor.

Haplotype
A person’s individual footprint of all tested genetic markers. Even the difference of a single genetic marker delineates a distinct haplotype.

Heredity
The total sum of genetic information that humans pass on from generation to generation

Melanin/Vitamin D/Skin Color
Melanin, the skin’s brown pigment, is a natural sunscreen that protects tropical peoples from the many harmful effects of ultraviolet (UV) rays. But when UV rays penetrate the skin they also produce beneficial vitamin D, so some exposure to them is necessary. This delicate balancing act explains why the peoples that migrated to darker, colder climes developed lighter skin color. As people moved to areas with lower UV levels, their skin lightened so that UV rays could penetrate and produce essential vitamin D. In some cases a third factor intervened: Coastal peoples who eat diets rich in seafood enjoy an alternate source of vitamin D. This is why some Arctic peoples, for example, can afford to remain dark-skinned even in low UV climes.

Mitochondria
Remnants of ancient parasitic bacteria that now help to produce energy inside the cell. A mitochondrion has its own genome, present in only one copy, which does not recombine in reproduction. This genetic consistency makes mitochondrial DNA a very important tool in tracking genetic histories.

Mitochondrial DNA or mtDNA
Genetic material found in the mitochondria. It is passed from females to their offspring without recombining, and it is thus an important tool for geneticists. The mtDNA is miniscule in contrast to the nuclear genome (~16,500 nucleotides versus 6 billion).

Nuclear Genome
The vast majority of your genome (apart from mtDNA) that is found in the cell nucleus

Nucleotide
A DNA building block that contains a base, or half of a “staircase step,” as well as sugars and phosphates that form the “railing.” Nucleotides join together to form DNA’s distinctive double helix shape.

Nucleus
The part of the cell in which chromosomes reside

Phylogeny
The evolutionary development of a species. Phylogeny is sometimes represented as a tree that shows the natural relations and development of all species. It can also be applied to the evolutionary tree of a specific region of DNA, in particular the Y-chromosome and mtDNA.

Population Genetics
The study of genetic variation in a species

Protein
A linear sequence of amino acids that is the building block of cells. Each protein has a specific function that is determined by the “blueprint” stored in DNA.

Recombination
The process by which each parent contributes half of an offspring’s DNA, creating an entirely new genetic identity. This process mixes genetic signals. Thus, nonrecombining DNA, which is passed intact through the generations, is most important in population genetics.

Replication
The process by which two DNA strands separate, with each helping to duplicate a new strand. During reproduction, the DNA double helix unwinds and duplicates itself to pass on genetic information to the next generation. Because bases always form established pairs (AT and CG), the sequence of bases on each strand will attract a corresponding match of new bases. Only occasional errors occur—about one for every billion base-pair replications.

RNA (Ribonucleic Acid)
Transfers the genetic “blueprint” that is stored in DNA during protein production. RNA has a single-stranded linear structure and a slightly different chemical composition from DNA.

Sequencing
Determines the order of nucleotides for any particular DNA segment or gene. The order of a DNA string’s base pairs determines which proteins are produced, and thus the function of a particular cell.

Sexual Selection
A special form of natural selection based on an organism’s ability to mate. Some animals possess characteristics that are more attractive to potential mates, such as the distinctive plumage of some male birds. Individuals with such characteristics mate at higher rates than those without, ensuring more next generation offspring will inherit the desirable trait. As generations procreate, the desirable trait becomes increasingly common, further boosting the sexual disadvantage for individuals who lack the desired trait. The effect can be particularly dramatic when one individual controls mating with a large number of potential partners.

Single Nucleotide Polymorphism
Small, infrequent changes that help to create an individual’s own unique DNA pattern. When a single nucleotide (A, T, G, or C) is altered during DNA replication due to a tiny “spelling mistake,” the genome sequence is altered.

Trait
Physical characteristics, like eye color or nose shape, determined by inherited genes

X and Y Chromosomes
Chromosomes that determine sex. Females have two X-chromosomes while males have one X and one Y. When chromosomes pair, the mismatched Y determines male gender. Because of the mismatch, part of the Y-chromosome does not recombine with the X during reproduction. The nonrecombining part of the Y-chromosome contains a sequence of DNA passed intact from males to their sons through the generations, giving population geneticists a useful tool for studying human history.