Anja Sturm

University of Göttingen


On classifying genealogies for general (diploid) exchangeable population models


Probability Seminar


9th February 2018, 3:30 pm – 4:30 pm
Main Maths Building, SM4


The genetic variation in a sample of individuals/genes depends on their relatedness
which is described by their genealogy. In this talk we consider classifying the genealogies
of exchangeable population models with fixed size N asymptotically as N tends to infinity.

In the first part of the talk we review classical results regarding the haploid Cannings model. Here, each individual
is represented by one of its genes and thus each offspring (gene) has a unique parent. In each generation,
the offspring vector to the N parents is exchangeable. With an appropriate rescaling the corresponding
coalescence processes describing the genealogy converge to a limit process. Möhle and Sagitov (2001) classified
all possible limit processes and showed that depending on the tail behavior of the offspring numbers the limit
process is Kingman's coalescent with coalescence of pairs or is given by coalescents with (simultaneous)
multiple mergers in which (several) larger groups may find a common ancestor at the same time.

In the second part of the talk we extend this result to diploid bi-parental analogues of the Cannings model.
Here, the next generation is composed of offspring of parent pairs, which form an exchangeable (symmetric) array.
Also, every individual carries two gene copies, each of which is inherited from one of its parents. Our result
classifies the limiting coalescent processes describing the gene genealogies. Using this general result we determine
the limiting coalescent in a number of examples of which some have been studied previously (in special cases)
and some are new. We also point out connections to the theory of random graphs.

This talk is based on joint work with Matthias Birkner (Universit\"at Mainz) and Huili Liu (Hebei Normal University).





Organisers: Tyler Helmuth, Ofer Busani

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