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Genealogy and Genetics
Left: DNA Double Helix
The Mayfair family tree presents a unique problem when it comes to genealogy and genetics. Often, what happens when two people
are too closely related to produce offspring that cannot survive to reproduce. It's a pileup of too many of the same genes
that results.
However, this does not mean it would be impossible for two people who are a little more distantly related to produce offspring
that can survive to reproduce. That threshold is generally considered to be at second cousins or more distant degrees of
relatedness. Well into at least the 19th century, it was still legal in the United States for first cousins to marry, which
many did.
What does this mean for our ancestry and our genetics? What effect does it have on genetics and does this happen in real
life? To help at least try to answer some of those questions, I decided to put together a brief tutorial of family trees
that contain a lot of pedigree collapse. And of course, I will explain what I mean by pedigree collapse...
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Genealogy of the Mayfair Family
Average Amount of DNA Inherited From Ancestors
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Generation
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Percentage on Average of DNA Inherited From Each Generation
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Parents
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50%
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Grandparents
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25%
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Great Grandparents
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12.5%
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2nd Great Grandparents
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6.25%
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3rd Great Grandparents
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3.13%
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4th Great Grandparents
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1.56%
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5th Great Grandparents
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0.78%
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Genealogy of the Mayfair Family
Likelihood of Detectable DNA In
Common
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Relationship
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23andMe
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AncestryDNA
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Family Tree DNA
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2nd Cousin or Closer
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>99%
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100%
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>99%
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3rd Cousin
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~90%
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98%
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>90%
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4th Cousin
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~45%
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71%
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>50%
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5th Cousin
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~15%
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32%
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>10%
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6th Cousin or Further
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<5%
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<11%
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<2%
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Right: DNA Giant Helix from the design in The Witches' Companion
by Katherine Ramsland
The averages in the charts are averages only. They are estimates based upon only one line of descent/one common ancestor.
Obviously, family trees like that of the Mayfairs are going to have vastly different averages of shared DNA because of how
many lines of descent any given Mayfair will have.
Mona Mayfair is described (by herself and others) as a "twentyfold Mayfair", meaning twenty different lines of descent. But
what does that mean, exactly?
In recent years, there has been a huge uptick in the amount of interest in our family trees, our genetics, and what they tell
us about genealogy. We have learned a lot of surprising things. We've learned these things through what is usually referred
to as "genetic genealogy".
The second chart above gives averages from three different DNA testing products. They each have their own testing thresholds.
Each of them can provide valuable information about our DNA.
While this site is not about true crime, I will say this: genetic genealogy has had an incredible impact on cold cases. Crimes
committed decades ago have been solved and unidentified persons have finally been identified, many times after decades of
being known as Jane or John Does with unique additional names to distinguish one Doe from another. One example: Jane "Arroyo
Grande" Doe, whose name, Tammy Corrine Terrell, was finally returned to her after 41 years.
So, how can we apply what we know now to the study of the Mayfair family tree?
The charts above come from this online article on Family Tree Magazine
DNA Q&A: Genealogical vs. Genetic Family Trees
DNA Sequencing
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Genealogy of the Mayfair Family
Terms to Know
Left: DNA Double Helix
Something I think is important to have a basic knowledge of when studying family trees like this one is a couple of terms.
This is the part where I have to advise caution. Family trees that show considerable pedigree collapse due to either or both
of the terms I will provide definitions for can be an extremely sensitive subject in a lot of ways.
So I want to make it clear that this study of the Mayfair family tree is one that describes characters in fiction. It is
here to help further examine the genealogy of the Mayfair Witches as part of the plot in the novels based on what is known
about genealogy and genetics. It is for this and no other reason that this is discussed on The Mayfair Witches Parlor.
Pedigree Collapse: In genealogy, pedigree collapse describes
how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree
of their offspring to be smaller than it could otherwise be. (Wikipedia)
Endogamy: The cultural practice of mating - usually in the form of marriage - within a specific social group,
religious denomination, caste, or ethnic group, rejecting those from others as unsuitable for marriage or other close interpersonal
relationships.
A long term pattern of endogamy in a region may increase the risk of repeated cousin marriage during a long period of time,
referred to as inbreeding. It may cause additional noise in the DNA autosomal data, giving the impressions that DNA matches
with roots in that region are more closely related than they are. (Wikipedia)
Incest: in·cest
noun
noun: incest
sexual relations between people classed as being too closely related to marry each other.
the crime of having sexual intercourse with a parent, child, sibling, or grandchild. -From Oxford Languages
Pedigree Collapse on Wikipedia
Endogamy on Wikipedia
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Genealogy of the Mayfair Family
DNA RNA Replication
Parlor Pages on Mayfairs and Genetics
Mayfair Witches Family Tree
Mayfair 500: How Cousins Are Made
Come Together - The Mayfair Witches
The Taltos and the Theory of Evolution
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Genealogy of the Mayfair Family
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