Explanation of DNA terms pertinent to the
haplogroup G discussion
Y-Chromosome -- a
portion of human DNA which is found only in
males.
It is passed from a father to his biological sons. Only minor
changes
in the make-up of Y-DNA occur from generation to generation. Most
other
portions of DNA result from random mixtures of DNA from mother and
father.
Haplotype -- the combination of values for an individual obtained
during lab testing at specific
DNA sites,
called DNA
markers. example
of a three-marker
haplotype:
DYS19 is 15, DYS390 is 23, DYS388 is
12
[The DYS nomenclature indicates the location of the
marker.]
The lab measures the lengths of STRs to obtain the value for each Y-chromosome
marker.
STR means short tandem repeat. STRs are junk segments of DNA
that repeat
themselves.
The variations in lengths are caused by mutations that increase or
decrease
the number of
repeats.
Haplogroup -- a genetic grouping to which a portion of the world's
population belong. With regard
to types
of the male Y-chromosome, each male can only belong to one major
haplogroup,
such as haplogroup A, B, G, J, or R. All members of each major group
share a common
male ancestor who long ago developed a DNA mutation called a SNP
[pronounced
snihp].
SNP stands for single nucleotide
polymorphism.
These SNP mutations occur much less frequently than STR mutations. The
haplotype STR
values
can often reliably predict the haplogroup, but SNP testing is needed for
complete
confirmation.
Subcategories exist within each major haplogroup, each defined by
additional SNPs. Those
who share the same subcategory SNP (such as G2b1) share a common male
ancestor.