One of the first stumbling blocks to understanding the results of yDNA analysis is the terminology.  This is my simple effort to help erase some of the mystery.  More importantly, I have links to other on-line resources that I consider as excellent examples of a very complex subject. 

Blair Family Genealogy - DNA 101, Y-Chromosome Testing
Charles F. Kerchner, Jr. - Genetics & Genealogy - An Introduction

Glossary of DNA terminology from Family Tree - for a more complete definition of DNA terminology

The Whiteside Family yDNA Project Results by Family Tree DNA

Family Tree DNA - Reading and Comparing DNA Test Results

If you really want to get into it, the following link is probably everything you ever wanted to know as a non-scientist about yDNA!

The Roper Report - Y-Chromosome Markers Families Comparisons

Although the above links provide good explanations, I felt it a good idea to cover some of the basics in, what I hope, is a layman's perspective.  I have written it in simple terms because I know that I have some younger readers, so please forgive me if I seem overly simplistic).  I have not arranged these terms in alphabetical order in the hopes that the earlier definition will help you to understand the definition that follows.  We'll see how that works!

DNA - Deoxyribonucleic acid (De-oxy-ribo-Nucleic Acid, enough said about that!)

yDNA - the DNA from the Y chromosome.

CHROMOSOME - A chromosome is simply a chemical structure found in the nucleus of cells (as an example, consider the yolk of a chicken egg is the nucleus of a very large single cell, while the egg of a human female is a very small single cell).  All humans have 23 chromosomes in the nucleus.  Of these, only two contain information that determines the sex of a person.  These two chemical structures when viewed through a powerful electron microscope actually resemble the letter "X" and "Y" and so are called the X and Y chromosomes.  How more straight forward can that be?  All the chromosomes in a cell pair up with a copy of itself, except for the X and Y chromosomes.  The Y chromosome pairs with the X chromosome and is passed on only from a man to his son.  The X chromosome will pair with another X chromosome and is passed from a mother to all of her children, but it is only passed on to her grandchildren by her daughters.  So, we have a pair, "XY" passed on to sons by their father, and a pair "XX" passed on by a mother to all of her children, but only by her daughters to her grandchildren.  This means that all males will have in the nucleus of their cells the "XY" and "XX" chromosomes; females will have the "XX" and "XX" chromosomes.  the "XY" chromosomes from your father's sperm causes you to develop as a male; the "XX" pair from your mother's egg, causes you to develop as a female.

NOTE ABOUT PRIVACY: yDNA is derived from the area of the chromosome known as "junk" DNA.  It was labeled as "junk" because at the time no one could determine its purpose.  It cannot be used in any way to identify an individual, except that the person is a male.  And, lucky for us, it can be used to determine ancestry. For this reason, it is safe to publish yDNA profiles on a public forum such as this.  The yDNA string does not tell us anything about the physical characteristics of an individual.  Unlike DNA used to identify parentage, it cannot be used to identify an individual since many individuals can have identical yDNA profiles.

Chart courtesy of
WWW.kerchner.com

yDNA cannot be used in any way to identify an individual (see the note on the left).

MARKERS - These are nothing more than specific locations on the Y chromosome.  These are called "Locus" (singular) and "Loci" (plural) which is simply latin for "location".  Each of these locations is assigned a code number by an international scientific committee to allow scientists to talk about a specific location in the DNA without going into a long discussion about exactly what marker they are talking about.  These code names are called "DYS" labels, which stands for DNA Y-Chromosome Segment.  I will use a simpler system of labeling the marker numerically 1 through 67 to make it easier for you to follow.  If you want to sound really scientific, you can use the DYS label, which I have also included.  Below is an example of a chart using the DYS names, along with my simple numbering system.  The top row is the DYS label and the second row is the one-up number of the marker. The third row is the value for the marker that I explain below:

This chart, by the way, are the values of the first twelve markers that we expect to find in direct descendants of the Whiteside clan.   They lived and died in the area of Yorkshire, and northern England and the border area of southern Scotland about the time of the Norman conquest of the British Isles. 

allele - A fancy term for the value of a particular marker.  In the example above, 13  24  14  11, etc. are the allele for markers 1 through 4.

STR - Short Tandem Repeat is the number of times a particular pattern that the chemical combinations of Adenine-Guanine (AG), and Cytosine-Thymine (CT) repeat together as pairs of rungs in the DNA ladder.  For example, if a combination of chemicals such as AG-CT (see DNA illustration above) repeats twelve times in a row, the value of that marker would be 12.  It is not really important for our purposes to know what those chemical combinations are exactly, and the value just gives us a reference number with which to work to show differences in the same DNA markers between one individual and another.

SNP - Single Nucleotide Polymorphism is a long label that means a change in a single nucleotide (a nucleotide is one of the A G C T chemicals) in the gene sequence.  A person has many of these alterations (mutations) that taken together uniquely identify that person.  In our report we will simply call these mutations, to explain the changes in particular markers.

haplogroup - this is a label that identifies the modern geographical area where different groups of our ancient ancestors lived.  These groups are given an identification code devised by another scientific committee so that these scientists do not get confused about the origins of people who display similar values in their markers.  Its interest to us is for the same reason - if you have enough curiosity to look up the definitions of these codes.  Most of our Whiteside and Whitsett participants belong to the haplogroup identified as coming from the western areas of Europe along the Atlantic Ocean.  That would include the British Isles, Scandinavia, Germany, Belgium, France, Portugal and Spain.  That haplogroup is given the code of R1b, or more precisely for our Whiteside's, R1b1b1 and R1b1b2.  I won't routinely use these codes unless it is worth noting something unusual.

haplotype - this is a person's set of values for the markers that have been tested.  People who show the same values in those same markers have the same haplotype. In the chart above, the marker values shown places us in the Whiteside haplotype.  I won't be using those codes unless it shows something unusual.

Please consider joining the Whiteside Family Association
www.whitesideancestry.org

yDNA RESULTS TABLE

ROWS: 
A - Subject Name or project number: Names used with permission.   For those who wish to remain anonymous, the numbers are the yDNA kit numbers used by the WFA in place of a person's given name and surname.
B - Ancestor Name: Earliest documented ancestor or proven head of subject's particular line.
C - WFA Family Number:  Whiteside Family Association Family Number created by Dr. Donald Whiteside, if known.  This number may change based on additional research.
D - Ancestral Origin: place of origin of earliest documented ancestor or place of origin of subject's family line. 
E - Haplotype: code (1R1B, etc.);  see explanation above
1-67 Marker Number and DYS Label: the 2nd column is the DYS labels used here simply for your information and so you can compare this chart with those that use only the DYS labels.

Colors indicate a difference from average in the WFA project.  The color of the cell or number indicates:
            Red Number - a marker predicted to mutate most frequently
           Blue Cell - a value higher than the project average
       Yellow Cell - a value lower than the project average

The mutations of themselves have no particular meaning; only the pattern of mutations that appear in compared yDNA markers have meaning when matched with other subjects.  The actual meaning can only be determined by documented genealogical research. 

NOTES:

(1) Kits No. 4296, 4626 - Ancestors William Whiteside(Whitsett) and Elizabeth Stockton of Tyrone and Rutherford County, N. C.  This is the family group that our Adam Whitsett family appears to be connected.
(2) based on matches in the yDNA results of other family 9000 members
(3)  It appears that this subject is actually closer to family 9000 than to 0957 suggesting that his branch needs much more research.
(4)  Based on these yDNA results, Warren believes his family surname has been flip-flopped between Whiteside and Whitsitt.  To date our research has been unable to determine if Warren's Quaker George Whiteside of Chester Co., Pennsylvania is actually the descendant of Quaker George Whitsitt who died in Chester Co. in 1736.
(5) These results were a surprise to us.  We were expecting results similar to kits 105189 and 164065.  Instead the results show that this donor was a direct descendant of legendary king Nial of the nine hostages, the 5th century Irish clan leader who supposedly kidnapped St. Patrick from his Roman family in London and kept him as a slave in Ireland. His name came from his practice of kidnapping important people from other clans and holding them until their clan swore allegiance to him or paid a ransom.  As a result he is credited with uniting Ireland and being its first true king.  Nial and his warriors raided all of the British Isles and the Atlantic seaboard of the European continent.  He fathered an immense number of children and today there are hundreds of thousands of direct descendants.  Because he lived before surnames were invented his descendants have many different surnames.
(6) This donor claimed descent from Samuel Whitsitt (1745-1815) of Montgomery County, Kentucky though his son Joseph.  After his results came back I was curious as to why he did not match the expected profile.  I did extensive document research which showed that Stewart Whitsitt, assumed to be the son of Joseph was actually fathered by someone other than Joseph.  This is now a new and unique line with many descendants with the surname Whitsitt.