molecular markers for fertility in farm animals

a genetic marker is a gene or dna sequence with known localization on a chromosome. it can be de-scribed as a variation that can be measured or detected by a suitable method, and can be used subsequently to detect the presence of a specific genotype. such variations occurring at chromosomal or dna level can serve as genetic markers. the progress in development of molecular markers suggests their potential use for genetic improvement in livestock species. animal fertility is a measure of reproductive success. in males, it can be defined as the ability of a male to produce semen that will result in a successful pregnancy. in fe-males, it can be defined as the ability of female to cycle and conceive normally to produce a viable off-spring. such a complex feature is under the influence of numerous genes, working together to produce func-tional gametes, promote early embryonic and fetal development and finally the delivery of a healthy off-spring. the heritability is relatively low for fertility so reproductive traits in general are well-suited for ap-plication of marker-assisted selection (mas). animal fertility is one of the most important economical traits in animal production. reproductive performance is controlled by the genetic make-up of the female and male, but in general it is largely affected by environment. phenotypic selection for reproductive traits can only be carried out after puberty while marker-assisted selection could be a tool of choice to improve animal fertility. the possibility of exerting selection criteria at the molecular level shortens the generation interval as the selection decision can take place early in the life of an animal. moreover, in consideration of the sex-limited nature of reproductive traits, genotypic information could allow for selection in the gender in which the trait cannot be directly observed. accordingly, there has been considerable interest in mapping and identifying genes involved in the regulation of reproductive traits and in elucidating their expression patterns. the current review aimed to discuss the efforts being made and the approaches currently used in the field of molecular markers and their application to fertility in farm animals.