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Y-DNA Glossary
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Base |
| In DNA, this can be either adenine (A), cytosine (C), guanine (G) or thymine (T). They are derived from either purine or pyrimidine. |
Base-pair |
| Two complementary bases joined by hydrogen bonds usually as part of the DNA molecule; base-pairing occurs between (purines and pyrimidines) i.e. between A and T and between G and C. |
Base sequence |
| The order of nucleotide bases in a DNA molecule e.g. AGTACGTA etc. |
Chromosomes |
| Chromosomes are bundles of tightly coiled DNA. Humans have 23 paired
chromosomes (22 pairs of autosomes and a single pair of sex chromosomes).
A single chromosome of each pair is passed from each parent to child. Each chromosome is formed when the DNA strand combines with lots of small proteins called histones. The DNA and histones automatically wrap themselves up into a shape that looks like an elongated letter X. |
Complementary sequences |
| DNA is made up of two long strands connected together along the middle
(a bit like a zip), where bases on one strand are bonded to bases on the
other side. If the base sequence is G-T-A-C on one side, the other side is always C-A-T-G, thus complementing each other. |
Cytosine |
| Designated by the letter C, it is a pyrimidine base. One of the four base molecules present in DNA. |
DNA |
| DeoxyriboNucleic Acid. The genetic material of organisms, usually double-stranded; a class of nucleic acids identified by the presence of phosphate, deoxyribose (a sugar), and the four bases. Often forms the familiar double-helix. Within DNA are the code-words needed to form proteins, although much of the DNA is termed 'junk DNA' and has no known function. |
DYS |
| D = DNA: Y = Chromosome; S = Single copy sequence. The DYS numbering scheme (e.g. DYS388, DYS390) for the Y-STR haplotype markers are controlled and administered by an international standards body called HUGO - Human Gene Nomenclature Committee - based at University College, London. |
Double helix |
| The familiar shape that two linear strands of DNA with complementary sequences assume when bonded together. |
Enzyme |
| A protein that can speed up a specific chemical reaction without being changed or consumed in the process. |
Gene |
| The functional and physical unit of heredity passed from parent to offspring; a sequence of DNA nucleotides on a chromosome. |
Genetic genealogy |
| The new field of family history research utilizing the Y-chromosome
and mtDNA to prove or disprove biological connections. The Y-chromosome
links the strictly paternal line (father to son), whilst mtDNA links the
mother to offspring line (mother to sons and daughters). For the vast majority of family history studies, the Y-chromosome is studied. |
Genetics |
| The study of the patterns of inheritance of specific traits. |
Genome |
| All the genetic material in the chromosomes of a particular organism; its size is generally given as the total number of base-pairs. In humans, 46 chromosomes make up the genome, with a total of 3 billion bases pairs of approx. 2 meters in length packaged into a tiny nucleus. |
Genome projects |
| Research and technology development efforts aimed at mapping and sequencing some or all of the genome of an organism. The improvements and lower cost of technology that genome projects have brought make possible the new field of genetic genealogy for genealogists. |
Genotype |
| The actual alleles present in an individual. |
Guanine |
| Designated by the letter G, it is a purine base. One of the four base molecules present in DNA. |
Haplotype |
| Genotype of genetically linked loci that are inherited in a block as a
single unit. Your Y-DNA haplotype is a set numbers, each number representing your allele at a given STR marker. Two or more haplotypes may be compared as a check for a genetic relationship. |
Haplogroup |
| Haplogroups are large groups that can be used to define genetic
populations and are often geographically orientated. For example, when the
Y-chromosome is tested, many males who live along the western coasts of
Europe belong to Haplogroup R1b (used to be called HG1), which belies the
historical movement of males along that coast. One way to think about
haplogroups is that a haplogroup is a branch on the tree of Homo Sapiens
and a haplotype represents the leaves of the tree. All the haplotypes that
belong to a haplogroup are leaves on the same branch. However, there is a strong correlation between haplogroups and haplotypes so given any particular haplotype, it may be possible to correctly determine the haplogroup without any further tests. |
Haplotype diversity |
| A measure of the uniqueness of a particular haplotype in a given population. |
Heredity |
| The transmission of characteristics (hair color, facial features, genetic disorders etc.) from one generation to the next. |
Junk DNA |
| Most of the DNA in our bodies is termed ‘junk DNA’. It is non-coding (isn’t used for making proteins) and thus does not control medical function but is probably involved in genomic organization. Genetic genealogy only looks at the markers within junk DNA and thus the Y-DNA test cannot derive any medical information. |
Locus (pl. loci) |
| Latin for place. See marker. |
Marker |
| Also called a Locus (pl. loci). A gene of a known location on a chromosome. See STR marker. FTDNA Y-DNA tests use 12, 25, or 37 STR markers. |
Microsatellite |
| See STR marker. |
Mitochondrial DNA |
| mtDNA - The circular DNA contained inside the mitochondria. The
mitochondria are small organelles residing in animal cells which provide
the power to the cell. They occupy about one-fifth of each cell. The mtDNA
is passed from mother to her offspring (both sons and daughters), but only
the daughter will pass it on.
The DNA sequence can be read and compared against a standard sequence (the Cambridge Reference Sequence) and deep (i.e. several thousands of years), but very broad genealogies can be deduced. An mtDNA haplogroup can usually be assigned for any given sequence. |
Modal |
| Statistical term - meaning the value at which an absolute or maximum occurs in the frequency distribution of the variate. |
Modal Haplotype |
| Any person who exactly matches the alleles found to be most common (Modal) among the descendants of a person. A person who matches 20 alleles while being 1 allele off in only 1 locus will be considered to be in the haplogroup, rather than in the family haplotype. |
MRCA |
| The Most Common Recent Ancestor between two people. For example, for two 1st cousins, their shared grandparent is the MRCA. If the cousins were both boys, they would share their grandfather’s Y-chromosome. |
mtDNA |
| See Mitochondrial DNA |
Multiplex reaction |
| Used in the PCR method, it utilizes a ‘cocktail’ of chemicals so that many different markers (or loci) may be copied and tagged at the same time. |
Mutation |
| Any inheritable change in DNA sequence. Mutations usually occur as a
result of miscopying by cell enzymes. Because the Y-chromosome has
relatively few regions that control genetic function and is mostly
‘junk-DNA’, mutations in this 'junk DNA' cause no adverse effects and can
therefore occur quite frequently. A mutation at an STR marker may cause a particular allele to change from 11 repeats to 12 repeats – the son will therefore carry the 12 allele. |
Mutation rate |
| The estimated rate of mutational change is estimated to be approximately one mutation per 500 transmission events (0.002) for any given STR marker. However, these changes are random and thus can take place at any time. |
Nucleic acid |
| DNA and RNA are both nucleic acids. They are long polymer structures made up of nucleotides. |
Nucleotide |
| A single unit of nucleic acid. In DNA they are composed of phosphate, deoxyribose (a sugar), and either a purine (for adenine and guanine) or pyrimidine (for cytosine and thymine) base. |
Nucleus |
| The central structure of a cell that contains the genetic material. |
PCR |
| Polymerase Chain Reaction - A process carried out
in a test tube that produces millions of copies of small sections of DNA.
Using a heat resistant enzyme (DNA polymerase) and a mixture of other
chemicals, cycles of hot and cold temperatures essentially photocopy a
particular marker (or locus) of the DNA many times.
Fluorescent tags are added to each copy so that they may be detected using laser analyzers. A technique called multiplexing enhances the process. |
Point Mutation |
| A change in a single base pair. |
Population |
| A group of individuals residing in a given area at a given time. |
REO |
| The Recent Ethnic Origin information is provided by each testee, and is only as accurate as the testee's knowledge. FTDNA instructs testees to answer "Unknown Origin" when their ancestor's origin is uncertain or not known. |
Restriction enzyme |
| A protein that recognizes specific, short nucleotide sequences and cuts DNA at those sites. Bacteria contain over 400 such enzymes that recognize and cut over 100 DNA sequences. Snake venoms are sometimes also used. |
Sequencing |
| Determination of the order of nucleotides (base sequence) in a DNA or RNA molecule or the order of amino acids in a protein. |
Sex chromosomes |
| X and Y-chromosomes - Chromosomes involved in sex determination. Females have two X chromosomes, males have one X and one Y-chromosome. The Y-chromosome is thus only found in males. |
SNP |
| Single Nucleotide Polymorphisms. An SNP test is used to confirm your haplogroup. |
STR marker |
| Short Tandem Repeats marker - A stretch of DNA
where a small base sequence (usually 2-6 base-pairs) repeats itself
several times, giving a particular allele. For example, at the STR marker
DYS391, the base sequence may read TCTA TCTA TCTA TCTA TCTA TCTA TCTA TCTA
where TCTA is repeated eight times. Choosing markers that have been proven to have high variation between and within populations is desirable. |
Thymine |
| Designated by the letter T, it is a pyrimidine base. One of the four base molecules present in DNA. |
TMRCA |
| Term used by population geneticists indicates the Time to the Most Recent Common Ancestor. |
Transmission event |
| The effective passing on of the Y-chromosome. |
Y-DNA |
| Non-recombining DNA determines whether a child will be a male or female. Y-DNA passes from father to son almost unaltered for long periods of time. It is approx. 60 million base-pairs long. |
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