Journal of Applied Genetics 44(3), 2003, pp. 375-378
Abnormal segregation of prion protein octapeptide-repeat alleles in cattle
Krzysztof WALAWSKI, Urszula CZARNIK, Robert WOJCIECHOWSKI, Chandra S. PAREEK
Abstract: The study was conducted on full-families of Black-and-White cattle obtained as 25 AI sire families and 355 cows, as well as their progenies, mostly heifers at the age of 1-3 months. The sire group was composed by the casual qualification of 10 PRNP 6/6 and 15 PRNP 6/5 individuals on the basis of accessible young progenies. The randomly selected group of cows is characterised by a very high frequency of PRNP 6/6 (74.9%), followed by lower frequency of PRNP 6/5 (24.5%) and a very low frequency of PRNP 5/5 genotype (0.6%). The progenies represent all expected genotypes, such as: PRNP 6/6 (60.5%), PRNP 6/5 (35.8%) and PRNP 5/5 (3.7%), respectively. Taking into consideration the genotypes of parents and progenies, the segregation of PRNP 6 and PRNP 5 alleles was analysed. Results of the non-informative mating variant of ♂ PRNP 6/6 × ♀ PRNP 6/6 (n = 87) are affected by the PRNP 6/6 progeny genotype in all cases. Subsequently, the results of mating variants ♂ PRNP 6/6 × ♀PRNP 6/5 (n = 29) and ♂ PRNP 6/5 ♀ PRNP 6/6 (n = 179) showed statistically non-significant differences in both above-mentioned alternations. The progeny group related from ♂ PRNP 6/5 × ♀ PRNP 6/5 parental mating obtained fully informative and most valuable results based on the presented research concept. In the common group of 58 calves, the genotype PRNP 6/6 is represented by 26 individuals (44.8 %), PRNP 6/5 – by 19 individuals (32.8 %) and PRNP 5/5 – by 13 individuals (22.4 %). Therefore, the theoretical genotype rate (25% : 50% : 25%) is drastically deformed and the differentiation between the observed and expected numbers of animals is statistically highly significant (χ2= 12.72; 2 df.). These differences are affected by two times higher PRNP 6/6 homozygous (χ2 = 9.12; 1 df.) and responsively by the low number of PRNP 6/5 heterozygous animals (χ2 = 3.45; 1 df.). Further investigations are carried out to explain the genetic determination of abnormal PRNP octa-peptide repeat allele segregation, which suggests possible lethal cis-trans linkage effects.
Key words: abnormal allele segregation, Black-and-White cattle, octapeptide repeat polymorphism, prion protein.
Correspondence: K. Walawski, Department of Animal Genetics, University of Warmia and Mazury in Olsztyn, ul. M. Oczapowskiego 5, 10-824 Olsztyn, Poland, e-mail: email@example.com.
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