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Adenine |
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Designated by the letter A, it is a purine base. One of the four
base molecules present in DNA. |
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Allele |
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One of several forms of a gene that can exist at a single location
(marker) on a chromosome. When STR's are measured on the Y-chromosome,
this corresponds to a different number of repeat units. For example,
for DYS19 where TAGA is the repeat unit, different alleles could
be 13, 14, 15 repeats of the TAGA unit etc.
A father will pass his Y-chromosome on to his son and thus the
son will inherit the same alleles (i.e. no. of repeat units).
Alleles will be changed if miscopied, resulting in a mutation.
Some alleles are more common in particular populations |
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Autosome |
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A chromosome not involved in sex determination. The human genome
consists of 46 chromosomes, 22 pairs of autosomes (numbered 1-22),
and one pair of sex chromosomes (the X and Y chromosomes). |
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Base |
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In DNA, this can be either adenine (A), cytosine (C), guanine (G)
or thymine (T). They are derived from either purine or pyrimidine. |
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Base-pair |
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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. |
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Base sequence |
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The order of nucleotide bases in a DNA molecule e.g AGTACGTA etc. |
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Chromosome |
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The structure by which hereditary information is physically transmitted
from one generation to the next. Humans have a total of 46, found
in the nucleus of each cell.
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. |
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Complementary
sequences |
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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. |
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Cytosine |
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Designated by the letter C, it is a pyrimidine base. One of the
four base molecules present in DNA. |
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DNA |
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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. |
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DYS |
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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. |
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Double helix |
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The familiar shape that two linear strands of DNA with complementary
sequences assume when bonded together. |
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Enzyme |
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A protein that can speed up a specific chemical reaction without
being changed or consumed in the process. |
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Gene |
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The basic unit of heredity; a sequence of DNA nucleotides on a chromosome. |
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Genetic genealogy |
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The new field of family history research utilising 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. |
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Genetics |
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The study of the patterns of inheritance of specific traits. |
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Genome |
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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 metres in length packaged into a tiny nucleus. |
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Genome projects |
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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. |
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Guanine |
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Designated by the letter G, it is a purine base. One of the four
base molecules present in DNA. |
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Haplotype |
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Your Y-DNA haplotype is a set of 21 numbers (if using 21 STR markers),
each number representing your allele at a given STR marker. Two or
more haplotypes may be compared as a check for a genetic relationship.
There are many haplotypes to be found from many different populations around the globe at www.yhrd.org
that may be used to compare haplotypes. Also, the Ybase
database can accept genealogical as well as haplotype data. |
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Haplotype diversity |
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A measure of the uniqueness of a particular haplotype in a given
population. |
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Haplogroup |
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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.
The Y-chromosome haplogroup of an individual is not
defined by their haplotype (because haplotypes are determined by
STR markers). Instead, they are determined by SNP's (single nucleotide
polymorphisms) where a single base changes e.g. from A to G. These
happen so rarely as to be considered unique.
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
(see Masterclass). |
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Heredity |
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The transmission of characteristics (hair colour, facial features,
genetic disorders etc.) from one generation to the next. |
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Junk DNA |
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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. |
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Locus (pl. loci) |
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Latin for place. See marker. |
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Marker |
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Also called a Locus (pl. loci). A gene of a known location on a
chromosome. See STR marker. The DNA Heritage Y-DNA test uses 21 STR
markers. |
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Microsatellite |
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See STR marker |
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Mitochondrial DNA |
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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. A mtDNA haplogroup
can usually be assigned for any given sequence. |
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MRCA |
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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. |
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mtDNA |
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See Mitochondrial DNA |
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Multiplex reaction |
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Used in the PCR method, it utilises a ‘cocktail’ of
chemicals so that many different markers (or loci) may be copied and
tagged at the same time. |
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Mutation |
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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. |
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Mutation rate |
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The estimated rate of mutational change is estimated to be approximately
one mutation per 500 transmission events (0.2%) for any given STR
marker. Using 21 different markers, it is reasonable to expect one
mutation every 24 transmission events. However, these changes are
random and thus can take place at any time. |
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Nucleic acid |
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DNA and RNA are both nucleic acids. They are long polymer structures
made up of nucleotides. |
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Nucleotide |
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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. |
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Nucleus |
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The central structure of a cell that contains the genetic material. |
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PCR |
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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 analysers. A technique called multiplexing enhances
the process. |
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Population |
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A group of individuals residing in a given area at a given time. |
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Restriction enzyme |
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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. |
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Sequencing |
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Determination of the order of nucleotides (base sequence) in a DNA
or RNA molecule or the order of amino acids in a protein. |
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Sex chromosomes |
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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. |
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STR marker |
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Short Tandem Repeats marker - A stretch of DNA where a small
base sequence (usu. 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.
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Thymine |
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Designated by the letter T, it is a pyrimidine base. One of the
four base molecules present in DNA. |
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Transmission event |
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The birth of a baby boy i.e. the effective passing on of the Y-chromosome. |
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Y-chromosome |
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The sex chromosome that instructs a foetus to grow into a baby boy.
It is passed down from generation to generation only through the male
line i.e. from father to son, father to son, etc. It is approx. 60
million base-pairs long. |
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