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Allele |
The number of repeats at an STR marker |
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Autosome |
A chromosome not involved in sex determination. The human genome consists of 23 pairs of chromosomes, 22 pairs of autosomes (numbered 1-22), and one pair of sex chromosomes (the X and Y chromosomes) |
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Compares the linked blocks of DNA across the 22 autosomal chromosomes. As autosomes contain random mixtures of DNA from ancestors, the degree of matching yields evidence of relationship – closer relatives have larger fragments of DNA in common |
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Cambridge Reference Sequence (CRS) |
The standard sequence of mitochondrial DNA (mtDNA) against which all other mtDNA is compared. The results of a mtDNA test cite only the markers that differ from this standard |
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A piece of DNA containing genes. It is the structure by which hereditary information is physically transmitted from one generation to the next |
DNA
( Deoxy ribo Nucleic Acid) |
The genetic material of organisms. Nuclear DNA is present in the cell nucleus and is usually structured into double strands, hence the familiar double helix. Within DNA are the codes needed to form proteins, although much DNA is termed 'junk DNA' and has no known function |
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Dominant / Recessive |
In a matched pair, each chromosome has genes that control the same function (eg eye colour). A dominant gene on one chromosome will override a recessive gene on the other |
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(DNA Y-chromosome Single copy sequence) numbers refer to particular STR marker locations on the Y-chromosome (eg DYS388, DYS390). |
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The basic unit of heredity; a sequence which is part of the long strands of DNA |
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Genetic Genealogy |
A new field of family history research, mainly 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). Recent autosomal DNA tests provide a way of comparing other family lines |
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Genome |
All the genetic material in the chromosomes of a particular organism. In humans, 46 chromosomes (23 pairs) make up the genome; approximately 2 metres in length packaged into a tiny nucleus – a complete copy found in each cell of the body |
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Large groups of genetic populations and often geographically orientated. eg the Y-chromosome haplogroup most common to males living along the western coasts of Europe is Haplogroup R1b. The Y-chromosome haplogroup of an individual is not defined by their haplotype, because haplotypes are determined by STR markers. Instead, haplogroups are determined by SNPs |
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A set of numbers, each number representing the allele at a given STR marker. Two or more haplotypes may be compared as a check for a genetic relationship. Closely related individuals have similar haplotypes |
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A gene of a known location on a chromosome. The greater the number of markers tested between 2 individuals, the better defined is their relationship |
Mitochondrial DNA (mtDNA) |
The circular DNA contained inside the mitochondria (containing fewer genes). mtDNA is passed from mother to her offspring (both sons and daughters), but only the daughter will pass it on. Deep but very broad genealogies (i.e. several thousands of years) can be deduced by considering mtDNA |
Most Recent Common Ancestor (MRCA) |
The Most Recent Common Ancestor between two people can be predicted by their DNA. The time when the common ancestor lived cannot be determined for certain, but can be estimated by the number of markers tested, the mutation rate and the number of mismatches |
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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 obvious adverse effects |
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Non-Paternity Event |
A situation where a family member does not have the same genetic profile as his alleged father, perhaps due to adoption, illegitimacy, etc. |
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The physical and behavioural characteristics of an individual (influenced by both genes and environment) |
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X- and Y-chromosomes are the chromosomes involved in sex determination. Females have two X chromosomes; males have one X and one Y-chromosome |
SNP (Single Nucleotide Polymorphism) |
(pronounced ‘snip’) A single DNA ‘letter’ differs from person to person. Some SNPs appear to be associated with variation in different people's phenotypes, while others appear to make no difference. SNPs account for 90% of the genetic variation in humans. Nearly all SNPs have mutated only once in human history so large proportions of the population have the same SNP |
STR marker (Short Tandem Repeat marker) |
A stretch of DNA where a small sequence repeats itself several times. An STR mutation adds or subtracts one or more repeats. STRs of the
Y-chromosome are useful for tracking exclusively male lines over the last few hundred years |
