That Unruly X….Chromosome That Is | DNAeXplained – Genetic Genealogy


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*Discovering Your Ancestors – One Gene at a Time*


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** That Unruly X….Chromosome That Is **

Posted on January 23, 2014 by robertajestes


Something is wrong with the X chromosome.  More specifically, something
is amiss with trying to use it, the way we normally use recombinant
chromosomes for genealogy.  In short, there’s a problem.

If you don’t understand how the X chromosome recombines and is passed
from generation to generation, now would be a good time to read my article,
“X Marks the Spot” about how this works.  You’ll need
this basic information to understand what I’m about to discuss.

The first hint of this “problem” is apparent in Jim Owston’s
“Phasing the X Chromosome” article.  Jim’s interest in
phasing his X, or figuring out where it came from genealogically, was
spurred by his lack of X matches with his brothers.  This is noteworthy,
because men don’t inherit any X from their father, so Jim’s failure
to share much of his X with his brothers meant that he had inherited
most of his X from just one of his mother’s parents, and his brothers
inherited theirs from the other parent.  Utilizing cousins, Jim was able
to further phase his X, meaning to attribute portions to the various
grandparents from whence it came.  After doing this work, Jim said the

“Since I can only confirm the originating grandparent of 51% my X-DNA,
I tend to believe (but cannot confirm at the present) that my X-chromosome


do x chromosomes recombine

Y chromosome - Wikipedia, the free encyclopedia


** Y chromosome **

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Human Y chromatid. See locus for notation.

The *Y chromosome* is one of two sex chromosomes (allosomes) in mammals,
including humans, and many other animals. The other is the X chromosome. Y
is the sex-determining chromosome in many species, since it is the presence
or absence of Y that determines male or female sex. In mammals, the Y
chromosome contains the gene SRY, which triggers testis development. The
DNA in the human Y chromosome is composed of about 59 million base
pairs.^[1] The Y chromosome is passed only from father to son, so analysis
of Y chromosome DNA may thus be used in genealogical research. With a 30%
difference between humans and chimpanzees, the Y chromosome is one of the
fastest evolving parts of the human genome.^[2] To date, over 200 Y-linked
genes have been identified.^[3] All Y-linked genes are expressed and (apart
from duplicated genes) hemizygous (present on only one chromosome) except
in the cases of aneuploidy such as Klinefelter's Syndrome (47,XXY) or XXYY
syndrome. (See Y linkage.)


· 1 Overview

· 1.1 Discovery
· 1.2 Variations

· 2 Origins and evolution

· 2.1 Before Y chromosome
· 2.2 Origin
· 2.3 Recombination inhibition
· 2.4 Degeneration

· 2.4.1 High mutation rate
· 2.4.2 Inefficient selection
· 2.4.3 Genetic drift

· 2.5 Gene conversion
· 2.6 Future evolution

· 3 Human Y chromosome

· 3.1 Genes

· 3.1.1 More common

· Y chromosome microdeletion
· Defective Y chromosome
· 3.1


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