Harden Hardin Harding yDNA Project

Definitions

·         Admixture  -  The action of mixing, the fact of being mixed, something added by mixing or a product of mixing  (used in conjunction with autosomal chromosomes).

·         Allele  -  One of the different forms of a gene or DNA sequence that can exist at a single locus, or one of the several alternate forms of a gene occupying a particular location on a chromosome.  Different alleles produce variation in inherited characteristics.  For STR markers, each allele is the number of repeats of the short base sequence.

·         Ancestry Information Marker (AIM)  -  AIMs are the subset of genetic markers that are different in allele frequencies across the populations of the world.  Most polymorphism is shared among all populations and for most loci the common allele is the same in each population.

·         Anthropology  -  The science of human beings;  especially:  the study of human beings in relation to distribution, origin, classification, and relationship of races, physical character, environment and social relations, and culture.

·         Autosomal DNA  -  Autosomal refers to any of the chromosomes other than the sex-determining chromosomes (i.e., the X and Y) or to the genes on these chromosomes.

·         Chromosomes  -  Chromosomes are bundles of tightly coiled DNA.  Chromosomes are paired threadlike ‘packages’ of long segments of DNA contained within the nucleus of each living cell.  Chromosomes are composed of a group of several thousand genes.  Modern humans are defined by 22 pairs of chromosomes, plus the X & Y sex chromosomes.  A single chromosome of each pair is passed from each parent to the child.  An X chromosome pair defines a female, while an X & Y pair defines a male (23 pairs in all).  Chromosomes are composed of DNA, which itself is composed of 4 nucleotides:  A (adenine),  T (thymine), C (cytosine),  and G (guanine).

·         DNA  -  Deoxyribonucleic Acid;  the main constituent of chromosomes – the double helix containing the chemical code that defines who and what we are.

·         DYS (number) -  The DNA Y-chromosome unique Segment (DYS) is also known as microsatellite loci (what we typically simply call a marker).  The numbering (or naming) scheme for the DYS is controlled by HUGO, the Human Gene Nomenclature Committee based at the University College in London.  When new markers are discovered, the scientist applies to HUGO for a DYS number for the marker, to give it a name.  Therefore, you can compare results of a Y-chromosome test conducted at any laboratory in the world, if the lab is using HUGO DYS numbers to define a marker.

·         Gene  -  A gene is the fundamental physical and functional unit of heredity.  A gene is a unit of heredity, capable of replication and mutation, occupying a fixed position on a chromosome, and passed on from parents to offspring during reproduction.

·         Genetics  -  The study of the function and behavior of genes.  Genes are bits of biochemical instructions found inside the cells of every organism from bacteria to humans.  Genes direct the synthesis of proteins.

·         Genome  -  All of the genetic material in a species.  The human genome is approximately 3,300,000,000 base pairs in length.

·         Genotype  -  The actual alleles present in an individual

·         Haplogroup  (or Clade)  -  A group of individuals sharing the same haplotype and who therefore share a common ancestor.

·         Haplotype (or sub Clade) -  The results of the Y-chromosome test that can be used for DNA matching.  A haplotype can be a single or unique set of chromosomes.  A Haplotype is a genotype of genetically linked loci that are inherited in a block as a single unit.

·         Locus (plural Loci)  -  The generic term for a specific location(s) in the genome.  A variable locus will have several possible alleles.

·         Modal  -  Modal comes from the statistical term ‘mode’, which means the value at which an absolute or maximum occurs in the frequency distribution of the variant.

·         Modal Haplotype (MH)  -  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 one (1) allele off on only one (1) locus will be considered to be in the Haplogroup, rather than in the family haplotype.

·         MRCA  -  This term refers to the Most Recent Common Ancestor (between two people) and is normally expressed in numbers of generations.

·         mtDNA  -   Mitochondria DNA  -  mtDNA is found in all cells of both males and females, but unlike the Y-DNA, mtDNA is passed down from generation to generation by a mother to her offspring.

·         Mutation  -  A permanent structural alteration in DNA (not a bad thing for the Y-chromosome).. These are small, but detectable changes that can occur during the DNA copying process during the transfer from father to son.  For the Y-DNA, it has been estimated that a mutation (an allele change for any given loci or marker) occurs (on average) once every 500 generations (10,000 to 15,000 years).  In the case of 12-markers being genotyped, there is a probability of at least one mutation every 40 generations.  Mutation rates vary dramatically among the various loci; therefore, studies are underway to establish better estimates for time between mutations for specific individual markers.  Eventually, we will be able to measure the number of generations to the MCRA much more accurately.

·         Point Mutation  -  A permanent change in a single base pair.

·         Polymorphism  -  The property of having more than one state or alternate sequence at a particular position.  The alternate states are called alleles.

·         SNP  -  Single Nucleotide Polymorphism  -  The SNP test of the Y-chromosome, establishes the deep ancestral markers that determine the specific Haplogroup for the person tested.  A SNP (pronounced snip) is a precise base pair position where different people are found to vary in sequence.  Generally two alternate alleles are found at a particular SNP.  At least 2,000,000 SNPs are now known and there may be over 30,000,000 in the human genome.

·         STR  -   Short Tandem Repeats.  A defined region of DNA containing multiple copies of short sequences of bases which are repeated a number of times; the number of repeats (the allele number) varies among individuals in the population and is the basis for comparing one person’s DNA to another individual.

·         TMRCA  -  This term refers to the Time to the Most Recent Common Ancestor between two people usually measured in number of generations.  An article in DNA 101 describes this calculation.

Y-Chromosome  -  The Y-chromosome is non-recombining DNA and it determines whether a child will be male or female.  The male Y-chromosome is passed down from generation to generation (father to son) normally unaltered for many generations.  The very minor changes (called mutations) that do occasionally occur at random are actually very helpful in assessing the results of DNA tests.  The Y-chromosome is the only human genetic material that escapes the continual reshuffling of parental genes with every new generation.  It is this unique characteristic of chromosome 23 that makes the Y-chromosome so important for genealogists.

 

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