Theoretical arguments suggest that in founder populations, even unrelated individuals share a number of genomic segments, or haplotypes, that are nearly identical over mega base-pairs. Such segments are called identical-by-descent (IBD). The recent sharp decline in genotyping costs revealed that IBD shared genomic blocks are abundant in many worldwide populations, including Ashkenazi Jews. When such shared haplotypes exist, they can be used to infer the population’s history, the effect of natural selection, or genes associated with a disease. Or, using sequence from one individual, one can infer, with high accuracy, some of the sequence of another individual, even if that other individual was only sparsely genotyped.
Theoretical modeling of the expected levels of IBD sharing in populations is crucial for many applications and for study design. In a number of papers, we developed the relevant theory, covering the following aspects of IBD sharing:
- The number of segments and the amount of genetic material covered by segments under models of population evolution. Specifically, we studied the coalescent with recombination and its approximations, including a novel “renewal” approximation .
- The average amount and the genomic span of segments shared between a single individual and a reference panel. Those quantities are important for effective design of sequencing studies .
In parallel, we applied IBD analysis to reconstruct the history of Ashkenazi Jews, Druze, and Irish Travellers [3,4,5], and developed a tool for fast extraction of IBD segments from simulated genomes . Current work focuses on the development of improved methods for demographic inference (i.e., reconstruction of the population history) based on sharing between multiple individuals, sex-specific demographic events, and ancient genomes.
 Carmi et al., Theoretical Population Biology, 2014 (link)
 Carmi et al., Genetics, 2013 (link)
 Carmi et al., Nature Communications, 2014 (link)
 Zidan et al., European Journal of Human Genetics, 2014 (link)
 Gilbert et al., Scientific Reports, 2017 (link)
 Yang et al., RECOMB 2015 (link)