I first heard about this theory when breeding horses. Since then, I try to apply it all the time. It explains how the female Chromosome X is larger and carries more genetic information than the Male Chromosome Y which is smaller and carries less genetic information. They noticed that females were responsible for transmitting certain traits or characteristics in the breed 68% of the time and males only 32%.

You can apply this theory to dogs when breeding. Now the first thing you need to know is how to read the peds using the X Factor. The second thing you need to know is the traits or characteristics expressed by each individual in that pedigree or at least the majority of them.

Let me show you how to look at a ped using the X Factor:

Let’s use an example of Mayday a male expressed as YX chromosomes

[attachment=1:dylvupqk]X Factor Male.jpg[/attachment:dylvupqk]


In order for Mayday become a Male, he received the Chromosome Y from his sire Gr. Ch. Yellow (Follow the Yellow Color Markings) and Yellow got his Y from Yellow John and Yellow John from Red Boy. Now, the question is Has Miss Jocko contributed to the genetic formation of Mayday? The X Factor theory says No. Why? Because Miss Jocko been a female as 2 X chromosomes and she gave 1 of her X chromosomes to Gr. Ch. Yellow but Yellow gave his Y chromosome to Mayday so no X chromosome information was passed on to Mayday from Miss Jocko. Mayday received his X chromosome from Dolly (follow the red marking) as she only had 2 X chromosomes to give one. Dolly receive her 2 X chromosomes one from Yazoo Cody and the other one from Lady in Red.


Now let’s do the same analysis using Dragon Lady as an example a full belly sister to Mayday. Dragon Lady is a female expressed as XX chromosomes.

[attachment=0:dylvupqk]X Factor Female.jpg[/attachment:dylvupqk]


Now Dragon Lady is a female and is made of 2 X chromosomes (XX). The X received from Dolly (Follow red color) is the only chromosome she could have received as Dolly itself is a female with only 2 X chromosomes.

Now let’s look at the top of the pedigree. Dragon Lady received the other X chromosome from her sire Gr. Ch. Yellow Male (YX). Gr. Ch. Yellow received that X from Miss Jocko. Now the question is Has Dragon Lady received any genetic information from Gr. Ch. Yellow John? According to the X Factor theory the answer is NO.

If you follow the colors you can understand how to apply the X Factor theory when you are evaluating a male and when evaluating a female. I strongly believe in applying this to all the breeding’s I do when selecting a male and a female to cross.

This approach will change the way you look at peds. It will give you a better perspective of the contributions that females brings to the breeding and will help you understand which individuals are actually contributing to the genetic characteristics of each individual.

Hope it helps more than it confuse.