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Friedrich J, Bailey RI, Talenti A, Chaudhry U, Ali Q, Obishakin EF, Ezeasor C, Powell J, Hanotte O, Tijjani A, Marshall K, Prendergast J, Wiener P. Mapping restricted introgression across the genomes of admixed indigenous African cattle breeds. Genet Sel Evol 2023; 55:91. [PMID: 38097935 PMCID: PMC10722721 DOI: 10.1186/s12711-023-00861-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2023] [Accepted: 11/24/2023] [Indexed: 12/17/2023] Open
Abstract
BACKGROUND The genomes of indigenous African cattle are composed of components with Middle Eastern (taurine) and South Asian (indicine) origins, providing a valuable model to study hybridization and to identify genetic barriers to gene flow. In this study, we analysed indigenous African cattle breeds as models of hybrid zones, considering taurine and indicine samples as ancestors. In a genomic cline analysis of whole-genome sequence data, we considered over 8 million variants from 144 animals, which allows for fine-mapping of potential genomic incompatibilities at high resolution across the genome. RESULTS We identified several thousand variants that had significantly steep clines ('SCV') across the whole genome, indicating restricted introgression. Some of the SCV were clustered into extended regions, with the longest on chromosome 7, spanning 725 kb and including 27 genes. We found that variants with a high phenotypic impact (e.g. indels, intra-genic and missense variants) likely represent greater genetic barriers to gene flow. Furthermore, our findings provide evidence that a large proportion of breed differentiation in African cattle could be linked to genomic incompatibilities and reproductive isolation. Functional evaluation of genes with SCV suggest that mitonuclear incompatibilities and genes associated with fitness (e.g. resistance to paratuberculosis) could account for restricted gene flow in indigenous African cattle. CONCLUSIONS To our knowledge, this is the first time genomic cline analysis has been applied to identify restricted introgression in the genomes of indigenous African cattle and the results provide extended insights into mechanisms (e.g. genomic incompatibilities) contributing to hybrid differentiation. These results have important implications for our understanding of genetic incompatibilities and reproductive isolation and provide important insights into the impact of cross-breeding cattle with the aim of producing offspring that are both hardy and productive.
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Affiliation(s)
- Juliane Friedrich
- Division of Genetics and Genomics, The Roslin Institute and Royal (Dick), School of Veterinary Studies, University of Edinburgh, Midlothian, UK.
| | - Richard I Bailey
- Department of Ecology and Vertebrate Zoology, University of Łódź, Łódź, Poland
| | - Andrea Talenti
- Division of Genetics and Genomics, The Roslin Institute and Royal (Dick), School of Veterinary Studies, University of Edinburgh, Midlothian, UK
| | - Umer Chaudhry
- School of Veterinary Medicine, St. George's University, St. George's, Caribbean, Grenada
| | - Qasim Ali
- Department of Parasitology, The University of Agriculture Dera Ismail Khan, Khyber Pakhtunkhwa, Pakistan
| | - Emmanuel F Obishakin
- Biotechnology Division, National Veterinary Research Institute, Vom, Plateau State, Nigeria
| | - Chukwunonso Ezeasor
- Department of Veterinary Pathology and Microbiology, University of Nigeria, Nsukka, Enugu State, Nigeria
| | - Jessica Powell
- Division of Infection and Immunity, The Roslin Institute and Royal (Dick), School of Veterinary Studies, University of Edinburgh, Midlothian, UK
| | - Olivier Hanotte
- International Livestock Research Institute (ILRI), Addis Ababa, Ethiopia
- School of Life Sciences, University of Nottingham, Nottingham, UK
- Centre for Tropical Livestock Genetics and Health (CTLGH), The Roslin Institute, University of Edinburgh, Midlothian, UK
| | | | - Karen Marshall
- Centre for Tropical Livestock Genetics and Health (CTLGH), ILRI Kenya, Nairobi, Kenya
| | - James Prendergast
- Division of Genetics and Genomics, The Roslin Institute and Royal (Dick), School of Veterinary Studies, University of Edinburgh, Midlothian, UK
| | - Pamela Wiener
- Division of Genetics and Genomics, The Roslin Institute and Royal (Dick), School of Veterinary Studies, University of Edinburgh, Midlothian, UK.
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Predicting recombination frequency from map distance. Heredity (Edinb) 2023; 130:114-121. [PMID: 36566319 PMCID: PMC9981558 DOI: 10.1038/s41437-022-00585-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2022] [Revised: 12/08/2022] [Accepted: 12/08/2022] [Indexed: 12/25/2022] Open
Abstract
Map distance is one of the key measures in genetics and indicates the expected number of crossovers between two loci. Map distance is estimated from the observed recombination frequency using mapping functions, the most widely used of those, Haldane and Kosambi, being developed at the time when the number of markers was low and unobserved crossovers had a substantial effect on the recombination fractions. In contemporary high-density marker data, the probability of multiple crossovers between adjacent loci is negligible and different mapping functions yield the same result, that is, the recombination frequency between adjacent loci is equal to the map distance in Morgans. However, high-density linkage maps contain an interpretation problem: the map distance over a long interval is additive and its association with recombination frequency is not defined. Here, we demonstrate with high-density linkage maps from humans and stickleback fishes that the inverses of Haldane's and Kosambi's mapping functions systematically underpredict recombination frequencies from map distance. To remedy this, we formulate a piecewise function that yields more accurate predictions of recombination frequency from map distance. Our results demonstrate that the association between map distance and recombination frequency is context-dependent and without a universal solution.
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