Research conducted since 1980 in relation to inheritance patterns and DNA testing of major genes for prolificacy has shown that major genes have the potential to significantly increase the reproductive performance of sheep flocks throughout the world. Mutations that increase ovulation rate have been discovered in the BMPR-1B, BMP15 and GDF9 genes, and others are known to exist from the expressed inheritance patterns although the mutations have not yet been located. In the case of BMP15, four different mutations have been discovered but each produces the same phenotype. The modes of inheritance of the different prolificacy genes include autosomal dominant genes with additive effects on ovulation rate (BMPR-1B; Lacaune), autosomal over-dominant genes with infertility in homozygous females (GDF9), X-linked over-dominant genes with infertility in homozygous females (BMP15), and X-linked maternally imprinted genes (FecX2). The size of the effect of one copy of a mutation on ovulation rate ranges from an extra 0.4 ovulations per oestrus for the FecX2 mutation to an extra 1.5 ovulations per oestrus for the BMPR-1B mutation. A commercial DNA testing service enables some of these mutations to be used in genetic improvement programmes based on marker assisted selection.
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