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Finocchiaro R., Budelli E., van Kaam J.B.C.H.M., Bovenhuis H., Portolano B., Caroli A.

RECESSIVE ALLELE FREQUENCY OF THE HR GENE IN THE VALLE DEL BELICE POPULATION. Finocchiaro R., Budelli E., van Kaam J.B.C.H.M., Bovenhuis H., Portolano B., Caroli A. I nternational W orkshop on M ajor G enes and Q TL in S heep and G oats – Toulouse 8 -11 December 2003. Introduction (1).

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Finocchiaro R., Budelli E., van Kaam J.B.C.H.M., Bovenhuis H., Portolano B., Caroli A.

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  1. RECESSIVE ALLELE FREQUENCY OF THE HR GENE IN THE VALLE DEL BELICE POPULATION Finocchiaro R., Budelli E., van Kaam J.B.C.H.M., Bovenhuis H., Portolano B., Caroli A. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  2. Introduction (1) • Valle del Belice sheep are a three way cross breed (Comisana, Pinzirita and Sarda dairy breeds). • It was approved as a breed in 1997. The population size is estimated at 60,000 mature ewes (1994). • In Valle del Belice sheep, lambs from both sexes can be born without any hair development (hypotrichotic individuals) due to the local farmers tendency of mating related animals. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  3. Introduction (2) • Hypothrichotic individuals are slaughtered soon after birth. • Carriers are kept in the flock; farmers believe the daughters of carrier rams have higher milk production. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  4. Introduction (3) • Congenital hypotrichosis in mammalian species consists of partial or complete absence of hair coat at birth. • In mammals there are several forms of hereditary hypotrichosis. These forms can be distinguished based on their hereditary transmission (autosomal dominant or recessive, and sex-linked). • The hairless (hr) gene is inherited in an autosomal manner with a recessive allele causing hypotrichosis in several species. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  5. Introduction (4) • A mutation in the hr gene, leading to a stop codon in exon 3, is resulting in congenital hypotrichosis in the Valle del Belice sheep (Finocchiaro et al., GSE 2003). • A PCR-SSCP test has been developed to locate the causative mutation. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  6. Aims • To verify the PCR-SSCP test on a larger number of Valle del Belice individuals. • To obtain an estimate of the recessive allele frequency in the population. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8-11 December 2003

  7. Material and Methods (1) • Genotyping • 67 blood samples have been collected in 7 farms in the western part of Sicily. • All animals had a normal phenotype except two with hypotrichotic phenotype. • Calculation was based only on  ++ (dominant homozygous for the normal phenotype)  and +hr (heterozygous carrier for the hairless phenotype) animals. • Hardy-Weinberg equilibrium was assumed. • PCR-SSCP test was applied to all the samples. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  8. Material and Methods (2) • Simulation of upper limit on the recessive allele frequency • To estimate the maximum allele frequency of the recessive allele given a ‘worst case’ mating scheme. ASSUMPTIONS: • All hrhr lambs are culled. • Frequency of the hrhr animals = 0  all remaining animals are either ++ or +hr. • F(+hr) rams = 100%  F(hr) rams =50% • Allele frequency in dams simulated using this mating scheme. • 20 generations with 10 million males and females, initial allele frequency of 0.001. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  9. Material and Methods (3) • Simulation of the distribution of the recessive allele frequency • Based on genotypes found in the sampled animals. • In each flock the  of ++ and +hr is used to obtain allele frequency in each flock (assuming H-W equilibrium). • All flocks were re-sampled in each repeat. • A flock was re-sampled generating new alleles for all animals using the allele frequencies of that flock. • Random number U[0,1> below the recessive allele frequency, then a recessive allele was assigned otherwise a dominant allele was assigned. • A total of 10 million repeats were performed. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  10. Results and Conclusions (1) • PCR-SSCP for the detection of 1312 mutation International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  11. Results and Conclusions (2) • Genotypes:Ignoring the 2 non-random hypotrichotic animals the hr frequency was =3.8%. International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  12. Results and Conclusions (3) • Maximum recessive allele frequency • The maximum allele frequency would be reached in 4 generations • Due to the selection of the +hr sires only • The genotypes of the new born lambs stabilize at: • ++ 35.4% • +hr 50.0% • hrhr 14.6% • The genotypes of the selected non-hypotrichotic dams: • ++ 41.4% • +hr 58.6% • Therefore the allele frequency for the dams: • + 70.7% • hr 29.3% International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

  13. Results and Conclusions (4) • Distribution of the recessive allele frequency • Sample estimate F(hr)=3.8% • Simulated expectation F(hr)=3.3% International Workshop on Major Genes and QTL in Sheep and Goats – Toulouse 8 -11 December 2003

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