DETECTION OF SOME FECUNDITY GENES IN OSSIMI BREED

Abstract

Animal genetic resources are essential components of agriculture development. They have contributing to food and agriculture for more than 12000 years. Sheep is one of the small livestock of choice in Egypt, where sheep meat production is more important than fiber production. Egyptian sheep population increased by 66.7% from 1961 to 2005.
There are three major breeds in Egypt; Rahmani, Ossimi, Barki. Barki ewes are sexually maturer earlier compared with Rahmani and Ossimi ewe lambs.
For increasing sheep meat production, the number of born lambs should be increased. This will be achieved through increasing both ovulation rate and litter size, these traits are genetically controlled. So studying genes affecting ovulation rate and litter size, which are known as fecundity genes, become imperative.
Since 1980, there has been increasing interest in the identification and utilization of major genes for prolificacy in sheep. Mutations that increase ovulation rate have been reported in the BMPR-1B (bone morphogenetic protein 1B receptor), BMP15 (Oocyte-derived bone morphogenetic protein 15) and GDF9 (growth differentiation factor 9) genes, and others are known to exist from the expressed inheritance patterns although the mutations have not been pinpointed.
Concerning the types of Fecundity genes in sheep (FecB, FecX and FecGH) the FecB was found to result from a mutation in the BMPR-1B (bone morphogenetic protein 1B receptor) (COGNOSAG, 1989), and is considered to be single mutation, duplication, or deletion event (Montgomery et al., 1992) that is expresses in oocytes and granulosa cells. Fec B is a dominant single autosomal gene located in chromosome 6, which has an additive effect on ovulation rate. One copy of FecB increases ovulation rate by about 1.5 fold and two copies of 3.0 fold. These extra ovulations in turn increase litter size by 1.0 and 1.5 fold (Davis, 2004). It is hypothesized that this mutation might reduce the signaling through the receptors of granulosa cells (Wilson et al., 2001) . The mutation that cause super prolificacy and the mutant sheep are characterized by precocious differentiation of ovarian follicles, leading to the production of large numbers of ovulatory follicles that are smaller in diameter than wild-type follicles.
The Booroola merino was the first breed of sheep where ovulation rate and litter size were shown to be affected by segregating major gene (Piper et al., 1985).
Four different fecundityX-linked gene, mutations have been discovered but each produced the same phenotype with four different alleles (FecXI, FecXH, FecXG, FecXB ). These are X-linked genes that increase ovulation rates in heterozygotes and cause infertility which might due to streak ovaries in homozygotes. (Davis, 2004) All these mutations can be detected directly by a PCR restriction fragment length polymorphism RFLP (Davis et al., 2002).
This study aimed to investigate the presence of the FecB and FecXI mutations in the main two Egyptian sheep breeds (Ossimi and Barki) through DNA studies using both the simple sequence repeats and forced restriction fragment length polymorphysim techniques by screening these two breeds for the presence of the Booroola fecundity genes.