Dear Hans, Apologies for the delay in replying to you. My original promise had slipped my mind. The following is an attempt to summarise our research and how it relates to the genetic status of the Jersey Breed. Email me back to let me know whether you would like to receive reprints of the original publications. Some can be sent via email as PDFs and some can be only be posted. We looked at three genetic systems to investigate the evolutionary origins and genetic history of cattle on a global scale. I hope you are not offended if some are all of the following basic genetics is known to you already. 1) Mitochondrial DNA (mtDNA) This is an unusual relatively small DNA molecule that is found within the energy-producing mitochondria in the cytoplasm of eukaryotic (complex) organisms. There are normally 100s of mitochondria in a typical cell (1000's in an unfertilised mammalian egg). Mitochondria from sperm do not contribute in any significant way to the mitochondrial pool of a fertilised egg and this means from a genetic point of view, that mtDNA is transmitted solely from females to their offspring. Mitochondria are descendents of free-living primitive bacteria that entered into a form of symbiotic relationship with other primitive cells hundreds of millions of years ago when eukaryotes first appeared. They retain some features of their evolutionary past including a slightly different genetic code and a relatively rapid mutation rate. The high mutation rate coupled with a lack of genetic exchange between maternal and the non-existent paternal mtDNA molecules means that mtDNA variation provide a remarkably clear picture of evolutionary relationship between closely related species or subspecies. In addition, it provides information about matriarchal domestic genetic history within a population (essentially how many different types of wild ancestors contributed to a domestic population and what are the most likely modern descendants). 2) 'Microsatellite' DNA variation Microsatellites are rapidly evolving stretches of non-functional DNA that are also widely used for genetic identification and forensic purposes. They provide genetic information concerning both the male and the female ancestors of an individual or population. They are particularly useful for detecting admixture and hybridisation between distinctive populations. For example, microsatellite analysis clearly shows that most African cattle populations are hybrids of taurine (Bos taurus) and zebu (Bos indicus) ancestry. They are also useful for detecting whether a particular breed or population has undergone a
population constriction or bottleneck at some stage during its genetic history. A population bottleneck can be detected as a noticeable decrease in microsatellite genetic variation compared to related populations (we might expect this to be likely with the Jersey because of their island origins and the early laws prohibiting the importation of cattle onto Jersey). 3) Y chromosome variation The Y chromosome is the mammalian male sex chromosome and contains relatively few genes. The genes it does contain however, are generally involved with the molecular signals that direct a developing embryo to become male. In addition, some are involved with sperm production.
Males receive their Y chromosomes from their father and an X chromosome from their mother Therefore males are XY. Females receive an X chromosome from their mothers and an X chromosome from their fathers. They are therefore XX.
In many respects the Y chromosome behaves like a male mirror-image of the mtDNA molecule. A large chunk of the chromosome does not recombine (undergo genetic exchange) with the X chromosome. This non-recombining portion can be analysed in populations in a similar manner to the mtDNA molecule. It provides a perspective on male genetic history. For example, in the case of domestic animals, it can indicate whether wild related species have contributed genetic material to domestic populations. In addition, because of the sex-biased distorted opportunity for reproductive success in many domestic species (one male can sire hundreds of offspring), it can provide an early-warning of gene flow between two related species or sub-species.
Our major results and conclusions (very briefly) 1) Analysis of all three genetic systems indicated that taurine (humpless) and zebu (humped) cattle are substantially different and should probably be considered separate species. The distribution of genetic variation in cattle demonstrates that taurine and zebu cattle were domesticated independently in two separate places. In addition these analyses shown that the genetic demarcation between breeds is very slight except when comparing across sub-specific lines between taurine and zebu or hybrid populations. In other words, although highland cattle may look more like yaks than cattle, their underlying genetic makeup is essentially identical to black and white Friesian or Jersey cattle. 2) Analysis of all three genetic systems indicates that African cattle are, for the most part, hybridæpart taurine, part zebu. 3) Analysis of mtDNA in modern populations and ancient aurochs bones indicates that European cattle are all descended from Middle Eastern populations that presumably moved into Europe with early Neolithic farmers.
Middle Eastern populations although complicated by subsequent zebu admixture, represent the source of European taurine genetic diversity. African taurine populations do not seem to trace their maternal ancestry to the Middle East and the early Egyptian culture many have domesticated wild North African cattle independently. We are continuing to work in more detail on the Y chromosome and this will shed much more light on the genetic history of African and European cattle. Implications for the Jersey breed.
The genetic data (and at this stage cattle are the most intensely studied species in this regard other than humans), show that there is nothing unusual about Jersey cattle. However, they do display low level of microsatellite genetic diversity. This is not surprising given their island origins. Based on a very small set of blood protein data, previous
researchers suggested that the Jersey breed may have Asian zebu ancestry, perhaps via an African route (Bangham & Blumberg,1958; Boston, 1954; 1963). This seems to have become a very durable myth and many animal breeders and livestock historians still talk about it. Archaeologists have known for years that this idea was probably rubbish. The molecular data confirms this. mtDNA, Y chromosomal variation and in particular microsatellite analysis shows that there is no trace of zebu ancestry in modern Jersey populations. The picture of Jersey cattle that emerges from the new data is the following: a) they are relatively lacking in genetic diversity, b) other than the reduced diversity, they are a typical northern European cattle population. Bangham, A.D. and B.S. Blumberg (1958) Distributions of electrophoretically different h!moglobin among some cattle breeds of Europe and Africa, Nature, 181, 1551-1552. Boston, E.J. (1954) Jersey cattle, Faber and Faber, London. Boston, E.J. (1963) Cattle breeds in Europe and Africa, in: A.E. Mourant and F.E.Zeuner (Eds.), Man And Cattle, Royal Anthropological Institute of Great Britain and Ireland, pp. 102-110.
Hope this helps, Remember, I will be glad to send you all the papers
that describe this work in more detailæjust email back indicating you would like to receive them. Best regards, David.
David MacHugh, Ph.D. Room 1.13 Department of Animal Science and
Production, Faculty of Agriculture, University College Dublin,
Belfield, Dublin 4. Ireland.