Single gene effects in Icelandic sheep – relation to practical breeding

1. Single gene effects in Icelandic sheep – relation to practical breeding Emma Eythórsdóttir Jón Vidar Jónmundsson Stefán Adalsteinsson

2. Early findings • Páll Zóphóníasson – the first geneticist in Iceland – early 1900’s • Pointed out several traits in cattle and sheep that he considered to be inherited as single genes • Often defects causing abnormal lambs/calves or stillbirths • Stefán Adalsteinsson – continued research on single gene effects – especially in sheep • many remarkable findings in the Icelandic sheep

3. Colour traits • Adalsteinsson described inheritance of colour in Icelandic sheep – first in 1960 • Three loci – 17 main colours • Variation is still present • Wool prices cause increased frequency of white • Non-white is 12-14 % of population at present

4. Special colour traits • Emphasis on grey for pelt production around 1960 • Production of dark-grey lambs by mating black ewes to homozygous grey rams • A small group of farmer is still specializing in grey pelt production – exported for special tanning – small industry

5. Pelts from spotted lambs, selected for maximum white colour with small dark spots Grey pelts – rather light grey

6. Special colour traits • Brown (moorit) wool collected overprize in the 1970’s -> temporary increase in frequency • Moorit is recessive to black • Knitting yarn in natural colours – regular production – variable demand

7. White colour - pleiotrophy • Awh – dominant allele at A locus – causes white colour • causes depressed fecundity – non-white ewes have more lambs than white ewes • estimated as -0,15 lambs per ewe mated (one copy) • Out-of-season breeding more frequent in non-white ewes

8. White vs. tan - albinism • Gene for white spots in non-white sheep eliminates tan fibres in white sheep • Tan in white is dominant – very frequent in white sheep • Albinisim – extremely rare - recessive

9. Fertility and litter size • The Thoka gene • increased litter size by 0.6-0.7 lambs per litter (one copy) • transfered into Cheviot in Scotland – same effect • The Loa gene – new mutation? • Inherited male fertility depression • identified in a single family – breeding rams selected for growth and conformation • 50 % of foetuses lost • Reciprocal translocation (13;20) Ewe 3117 at Skriduklaustur with quadriplets

10. Horn growth • Two alleles at the Ho locus – horned or polled in both sexes • Polled with incomplete dominance – heterozygotes may grow horns or scurs • Basis of strain formation within the breed • Four horns – HN locus

12. Genetic defects • Genetic defects and lethal genes are extremely rare • Spina bifida – lameness of hindquarters – autosomal recessive • Crippled forelegs – autosomal recessive • found in certain family lines – carriers with high score for conformation • Yellow carcass fat – unacceptable meat • autosomal recessive – family lines with some popular breeding rams – still found at low frequency

13. Newborn lambs with crippled legs The defect was spread in South Iceland around 1980 through the use of two AI sires that carried the defect. Increased frequency in top breeding flocks in the area. Still present at low frequency

14. Carcass showing the phenotype of yellow fat (left) Normal carcass to the right Carrers are still found in some of the top breeding stock

15. Scrapie • Variation in PrP gene connected to susceptibility • Variable aminoacids at codons 136, 154 and 171 • Codon 171 is monomorphic in Icelandic sheep (glutamine) • Three alleles found: • VRQ – increased risk (9 %) • ARQ – wild type (87 %) • AHQ – protective (4 %) • ARR allele – most protective in other breeds – not found in the breed so far

16. Scrapie • All AI rams are genotyped for PrP • results known to breeders – not included in overall selection goal • Selection program initiated at one farm with hight frequency of AHQ in the herd • Export markets for lamb may require genotypes in the future?

17. Single genes - implications • Gene frequencies are quickly changed through use of AI • undesireable recessive traits or defects may increase in frequency through the use of popular sires • Relatively easy to put desirable traits to use (Thoka) • Many of the traits found have not been scientifically tested or genes identified • scope for many research projects – markers and gene identification

18. THANK YOU!