genome and the heritage of tracing the roots

If the Y chromosome traces the male lineage back through history,
then the mitochondrial genome (mtDNA) can be considered its
female counterpart. Mitochondria are self reproducing structures
found inside the cells of all higher organisims, typically present
in hundreds of copies per cell.

They are responsible for generating most of the energy used by the cell.
Because the sperm head has no mitochondria, they arepassed solely from
mother to offspring. One region of particular importance in mtDNA is the
hypervariable region( HVR 1 & 2) where the rate of mutation is 100 times
of the nuclear genome. Because of its much shorter length( several hundred
nucleotides versus millions of nucleotides for the Y),HVR can be quickly
scanned to reveal many informative mutational events that have been passed
through the maternal line.




Y chromosome determines the sex in humans. While all other chromosomes
arefound in matching pairs, Y mismatch with partner determines gender.
men having mismatched X and Y while women have two X chromosomes. Because Y
does not have a match, most of it , the NRY, non recombining region escapes the
shuffling process known as recombination that occurs every generation in rest of 
genome. Thus except random mutional events, Y is passed donw through a purely
male line.

Genetics Glossary

Allele 

Variant form of a gene. 

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 
His work became the foundation of modern evolutionary theory. 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 unfortunate 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 (see detailed entry below). 

Double Helix 
The shape of DNA, much like 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 the key to the development of brain regions associated with speech. FOXP2's discovery suggests that the development of language may be tied to a genetic mutation that could have occurred some 50,000 years ago, in the same time range as the first great human migrations out of Africa. 

Genes 
Segments of DNA that are the basic functional units 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. 

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

Haplogroup 
Branches on the tree of early human migrations and genetic evolution. 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 most recent common ancestor. Haplogroups often have a geographic relation. 

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 also 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. That means that some Arctic peoples, for example, can afford to remain dark-skinned even in low UV climes. 

Mitochondria 
A remnant of an ancient parasitic bacteria that now helps 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 thus is an important tool for geneticists. 

Nucleotide 
A DNA building block which contains a base, or half of a "staircase step," and sugars and phosphates which 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. 

Population genetics 
The study of genetic variation in a species. 

Proteins 
Linear sequences of amino acids that are the building blocks 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, so that nonrecombining DNA, passed intact through the generations, is most important to 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 
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 which 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 
The physical characteristics, like eye color or nose shape, which are determined by inherited genes. 

X and Y Chromosomes 
Chromosomes which 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.