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Sent: 22 June 2005 15:01
Subject: 71: Molecular markers - Populations the same? - Inbreeding
This is Miguel A. Toro, again.
1. In Message 65, M.S. Tantia says: "I certainly agree that molecular characterization with microsatellite markers, which are mostly neutral to selection, are excellent tools to study population parameters and identify unique populations/breeds requiring efforts for their improvement and conservation".
I have two comments: a) Which are ‘exactly’ these tools and how should be applied?
b) I think that the important parameters to consider are the phenotypic ones: adaptation to specific environments, possession of traits of economic importance or unique traits, cultural or historical values, etc..(see "Genebanks and the conservation of farm animal genetic resources", 1999, edited by J.K. Oldenbroek). To use molecular markers is not harmful as long as we recognize its subordinate relevance in this context.
2. In Message 66, Salah Galal says: "Of course molecular techniques can establish with a certain degree of probability if these populations are/are not the "same". "
My comment is again: Are there molecular techniques that allow us to establish objectively that two populations are/are not the same with a certain probability? Which are these molecular techniques ?
3. In message 69, S.G. Tan says: "In Malaysia, it has been found through the use of molecular genetic markers (be they protein level ones like allozymes, whenever possible or DNA markers like microsatellites, when the need arises) that the level of genetic variation is low in many cultured stocks of prawns and seabass. This has resulted in low fertility levels and abnormalities being found in them. Such information has vast economic implications because if the situation is not remedied through the introduction of more genetic variation, the cultured stocks will continue to deteriorate with time and the aquaculture industry will suffer economically. Hence, in developing countries, it does make sense to invest in genetic marker studies of economically important species".
My comment is the following: Inbreeding depression is well known since 1900 (at least) and, in all conservation (and genetic improvement) programs in domestic species, precautions are taken to avoid this problem. In general, the optimal strategies require the knowledge of pedigree, but some other more simple things can be done (for example, subdividing the population and interchanging individuals among them). Obviously, these things are well established and were utilized before molecular markers existed. Also, from experimental work (with mice, Drosophila, pigs, trout etc.) it has been many times verified that if you do deliberate inbreeding (by brother-sister mating, for example) you will observe the catastrophic consequences of inbreeding. I cannot see what molecular markers can add to this huge amount of information (obviously in some of these experiments people also observe a decrease in the heterozygosity of microsatellites). On the other hand, molecular markers hardly can be useful in the management of a conservation program. However, I do not want to be totally negative. I think that molecular markers could be useful in some settings to obtain or verify pedigree information (by paternity analysis for example) that is the crucial information for a correct management of a conservation program.
Miguel Angel Toro Ibanez
Departamento de Mejora Genetica Animal
Instituto Nacional de Investigacion y Tecnologia Agraria y Agroalimentaria (INIA)
Carretera La Coruna km. 7 28040
Tel: 34 913476807
Fax: 34 913572293
e-mail: toro (at) inia.es
[As part of an European Union (EU) Concerted Action, 3 meetings were held in 1997 and 1998 in which several aspects of conservation of genetic variation in farm animal populations in Europe were presented and discussed in order to develop guidelines for the cryoconservation of farm animal genetic diversity. Much attention was paid to the integration of the ex situ conservation in a genebank in programs for in situ conservation in EU circumstances. Geneticists from Scotland, Norway, Finland, France, Italy, Spain, The Netherlands and from FAO participated in these meetings. In a fourth meeting in 1998, they synthesised these aspects and discussions for publication in the 8-chapter book edited by J.K. Oldenbroek, referred to near top of the message - available at http://dad.fao.org/en/refer/library/reports/GenebanksNL.pdf ...Moderator].