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EMMANUELLE GENIN: Hello my
name is Emmanuelle Genin.
I work in Brest in
the southwest of France,
and today I am going to talk
about the inference of relatedness.
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So, first of all, we need to define
what is meant by relatedness.
Relatedness defines the fact
that individuals are related.
And two individuals
are related if they
share at least one
common ancestor.
To illustrate, let us consider
the three-generation genealogy
of Jack and Chloe.
So Jack and Chloe are related.
They are, in fact, first cousins.
And their fathers,
James and Albert,
are brothers so
they are also related.
They have two common
ancestors, their grandparents,
Robert and Mary.
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Relatedness has some
genetic consequence
in terms of allele sharing.
Indeed, coming back to
the special case of Jack and Chloe
and considering a given position
on their genome, a position that we
call the locus,
we see that it's possible
that they have received
at this locus, two alleles
that are identical-by-descent.
And here on the figure, it is
shown for the case where they
have received two alleles
identical-by-descent
from their grandfather Robert.
So in fact, this alleles
are identical-by-descent
because Robert birthed
the same allele to James
and Albert, so his two sons.
And then James and Albert passed
this allele to Jack and Chloe.
So this shared allele is a copy of
a single allele that was present in Robert,
but it could have also been
from the grandmother Mary.
And in fact, these two events
are mutually exclusive.
Jack and Chloe cannot
share both an allele from
Robert and Mary at a given locus.
It is also possible that they shared
no allele if James and Albert did
not receive the same
allele from Robert or Mary,
or if they did not pass their
shared allele to Jack and Chloe.
